Explorations An Introduction to Astronomy 7th Edition Arny Solutions Manual

Visit https://testbankfan.com to download the full version and
explore more testbank or solutions manual
Explorations An Introduction to Astronomy 7th
Edition Arny Solutions Manual
_____ Click the link below to download _____
https://testbankfan.com/product/explorations-an-
introduction-to-astronomy-7th-edition-arny-solutions-manual/
Explore and download more testbank or solutions manual at testbankfan.com

Here are some recommended products that we believe you will be
interested in. You can click the link to download.
Explorations An Introduction to Astronomy 7th Edition Arny
Test Bank
https://testbankfan.com/product/explorations-an-introduction-to-
astronomy-7th-edition-arny-test-bank/
Explorations Introduction to Astronomy 8th Edition Arny
Solutions Manual
https://testbankfan.com/product/explorations-introduction-to-
astronomy-8th-edition-arny-solutions-manual/
Explorations Introduction to Astronomy 8th Edition Arny
Test Bank
https://testbankfan.com/product/explorations-introduction-to-
astronomy-8th-edition-arny-test-bank/
Environmental Economics An Introduction 7th Edition Field
Solutions Manual
https://testbankfan.com/product/environmental-economics-an-
introduction-7th-edition-field-solutions-manual/

Aging and the Life Course An Introduction to Social
Gerontology 7th Edition Quadagno Solutions Manual
https://testbankfan.com/product/aging-and-the-life-course-an-
introduction-to-social-gerontology-7th-edition-quadagno-solutions-
manual/
Introduction to Policing 7th Edition Dempsey Solutions
Manual
https://testbankfan.com/product/introduction-to-policing-7th-edition-
dempsey-solutions-manual/
Introduction to Hospitality 7th Edition Walker Solutions
Manual
https://testbankfan.com/product/introduction-to-hospitality-7th-
edition-walker-solutions-manual/
Introduction to Flight 7th Edition Anderson Solutions
Manual
https://testbankfan.com/product/introduction-to-flight-7th-edition-
anderson-solutions-manual/
Atmosphere An Introduction to Meteorology 13th Edition
Lutgens Solutions Manual
https://testbankfan.com/product/atmosphere-an-introduction-to-
meteorology-13th-edition-lutgens-solutions-manual/

Chapter 10 The Outer Planets
1
© 2014 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in
any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
CHAPTER 10 THE OUTER PLANETS
Answers to Thought Questions
1. If Jupiter were closer to the Sun it would become hotter. The hydrogen and helium in the
atmosphere would move faster, causing some of it to be lost. With enough heating, it might
evaporate down to a rocky/iron body similar to, but larger than the Earth. [Consider the
implications of this idea, in the context of migrating planets].
2. Europa’s and Enceladus’s relatively crater-free surfaces imply that some process has
resurfaced them and destroyed old craters. One possibility is that liquid water has erupted
from their interiors and flooded parts of their surfaces, covering old craters, and then freezing
into a new solid surface.
3. Overall it would be a lot like having a comet in orbit. The average densities of Callisto and
Ganymede are 1.94 and 1.85 g/cm3
, and Tethys and Dione, which appear in Figure 10.19 to
strongly resemble our Moon, have an average density even less (0.98 and 1.49 g/cm3
). The
Moon’s average density is 3.34 g/cm3
. The Moon is made of rock; the gas giant moons are
made largely of ices. If one were in orbit around the Earth, some of these ices would melt
from the combination of increased sunlight and also perhaps from tidal heating from
interaction with the Earth. Exactly how much melting would occur would depend in part on
how effectively the surfaces absorbed sunlight (the average temperature on the Moon is still
less than freezing) but once the process started, it would releasing methane, ammonia, and
water. Evaporated water, methane, and/or carbon dioxide if any formed or was present could
potentially form a thin atmosphere that could create a greenhouse effect to further melt the
surface and replenish the atmosphere. The surface features would disappear as the surface
melted, and some of the gases would be lost to space, much like a comet tail, which would be
quite a sight. The moons would show phases and cause tides similar to our Moon. With a
mass about twice that of the Moon, Ganymede would cause tides twice as strong at the same
distance. Callisto is only about 40% more massive than the Moon so its tides would be a little
stronger. Tethys and Dione each have about 1% as much mass as our Moon, so their tides
would be very weak (weaker, in fact, than the Sun’s). Over time, the objects would shrink as
their icy layers evaporated, leaving behind a much smaller rocky core.
4. The Roche limits are 2.44 times the planet’s radii:
Planet Limit Interior Moons in Table 7
Saturn – 147053 km Pan, Atlas, Prometheus, Pandora
Uranus – 62364 km Cordelia, Ophelia, Bianca, Cressida
Objects can survive inside the Roche limit if they are held together by a force other than their
own gravity. These moons would be expected to small and irregular, since if they were large
enough for gravity to smooth them into spheres, they would be subject to destruction by the
tidal forces. These bodies must be held together by the (chemical) strength of the rock or ice
that makes them up.

2
5. Titan’s features are similar in shape to those found on the Earth. More or less, material in
the atmosphere appears to “rain” out of clouds and drain across the surface, reshaping rocks
and forming rivers and lakes. Winds push the dunes around. The “volcanoes” erupt gases and
material which resurfaces the moon. However, all of this occurs at much lower temperatures
than for the terrestrial analogs. The rocks are made of very cold ice. At such temperatures, ice
is as hard as steel or rock on Earth. The liquid in the lakes is made of hydrocarbons—
ethane—not water (oxygen and hydrogen). Most different of all, the volcanoes do not erupt
hot, molten rock, but are eject more or less cold molten hydrocarbons and water (though they
are hotter than the surrounding surface and atmosphere). The “volcanoes” are more like
Earth’s geysers than its volcanoes.
6. The Earth’s sky is blue because small particles in the atmosphere scatter short wavelengths
of light (blue light) more effectively than they scatter longer wavelengths (red light). The
effect is most pronounced at sunset: the Sun appears reddish, because blue light is scattered
out of the line of sight, but the opposite side of the sky looks blue (scattered sunlight). The
situation is similar on Uranus, but the scattering particles are methane crystals, not dust, and
that causes an important difference. As seen from outside, ice crystals of methane in the
atmosphere scatter and reflect blue sunlight, making the atmosphere appear blue. However,
the ice crystals also strongly absorb the red photons, unlike the scattering particles in Earth’s
atmosphere. Whereas the Sun appears redder from the Earth’s surface because blue light is
scattered out of the line of sight, from deep in Uranus’ atmosphere, the Sun should actually
appear bluer than it would otherwise because the red photons have been absorbed. However, it
seems unlikely that one would be able to see the Sun itself through the methane-ice clouds
and haze. The scattering of blue light by the ice crystals suggests that at least in the upper
atmosphere, the sky would appear blue from inside as well—but again, hazy and cloud-filled.
7. Uranus’s moons orbit its equator. Though tilted the system is extremely regular. The
moons are made of more or less the same kinds of material as other gas giant moons (and gas
giants, minus the hydrogen and helium)—frozen volatiles and rock. Together these details
imply that, similar to how the Earth’s moon was formed, material that splashed out of Uranus
during a major collision coalesced into the orbiting moons. If the moons had formed prior to
the collision, tidal forces and the angular momentum of the Uranus-moon systems would have
opposed the forces in the collision trying to “tip” the planet (think of tilting a gyroscope).
Some of the moons might have been ejected and others could have irregular orbits. [However,
if Uranus was tipped slowly, through gravitational interaction with Saturn, the same tidal
forces might have helped also slowly tip the moons’ orbits.]
8. Uranus and Neptune are less massive than Jupiter and Saturn, and have lower escape
velocities. Even though these planets are colder, the lighter gases can still escape their weaker
gravitational fields.
9. Wind systems on the gas giants are driven by heat escaping from the interior; the bands
result from the planets’ rapid rotation and the Coriolis effect. Neptune, being more massive,
should have more internal heat than Uranus, but it is also farther from the Sun, so it is colder
at the surface. This large temperature difference drives the circulation more strongly than it

3
would be driven on Uranus. Uranus, being tipped, has disruptions to this kind of heat-flow
driven circulation because of its extreme seasons. It seems possible that Uranus might exhibit
atmospheric patterns more like the other gas giants during the parts of its orbit when one
hemisphere is not perpetually pointed at the Sun.
10. STUDENTS’ OPINIONS WITH EXPLANATION.
Answers to Problems
1. The time, t, it takes light to travel a distance, D, is t = D/c, where c is the speed of light, 3
× 10
5
km/s. Using the average distances from the Sun from the Appendix,
Jupiter: t = D/c = (778.3 × 10
6
km) / 3 × 10
5
km/s = 2.5 × 10
3
s = 42 minutes
Uranus: t = D/c = (2870 × 10
6
km) / 3 × 10
5
km/s = 9.6 × 10
3
s = 160 minutes
Since it would take twice this time to know if a command sent to a satellite was received and
acknowledged, clearly equipment sent to the outer solar system needs to be highly
automated—satellites could move pretty far off course just during the time to send and receive
one command! Likewise, manned missions would have to make time-sensitive decisions on
their own.
2. Again, we need to use t = D/v. This time the distance traveled is Jupiter’s circumference at
the equator; the time is the period of rotation.
Distance = circumference = 2πR = 2π × 71492km = 449197 km.
v = D/t = 449197 km / 9.9 hr = 45373 km/hr.
3. Let’s use Europa to calculate Jupiter’s mass using the moon’s orbital data. The modified
form of Kepler’s third law is M = 4d3
/GP2
with M in kg, P in seconds and d in meters. For
Europa, d = 671 × 10
3
km and P = 3.55 days × 24 hr/day × 3600s/hr = 306,720 s.
M = 4d3
/GP2
= 4 (671 × 10
3
km × 10
3
m/km)3
/ (6.67×10
-11
m3
kg-1
s-2
× 3067202
s2
)
= 4 (×10
26
)/(6.27 kg-1
)
= 1.9 × 10
27
kg
This is the same value as given in the Appendix for the mass of Jupiter.
4. There are several ways to solve this problem. First, through direct calculation:
Jupiter’s density, , is 1.33 g/cm
3
. Saturn has a total mass of 5.68 × 10
26
kg = 5.68 × 10
29
g. If
Saturn was a sphere with Jupiter’s average density, the volume of that sphere would be
V = M/ = 5.68 × 10
29
g / (1.33 g/cm
3
) = 4.27 × 10
29
cm
3
.
The radius of a sphere of this volume is:
r = [(3V/(4)]
3
= [(3 × 4.27 × 10
29
cm
3
/(4)]
3
= 4.67 × 10
9
cm = 46,700 km.
Jupiter’s radius is 71,492 km, so Saturn’s radius would be about 65% as large. (Saturn’s
actual radius is 60,268 km, so it would be 77% the size it currently is.)

4
The answer can also be found by using proportional reasoning. If Saturn and Jupiter have the
same density, then the volume will depend only on the mass. The volume of a sphere grows as
radius cubed. The ratio of Saturn’s mass to Jupiter’s mass is
5.68 × 10
26
kg / (1.90 × 10
27
kg) = 5.68 × 10
26
kg / (19.0 × 10
26
kg)
= 5.68 / 19 = 0.2989.
Therefore, if Saturn had Jupiter’s density, it’s volume would be 0.2989 times the volume of
Jupiter, so the radius would be (0.2989)
1/3
= 0.669 times the current radius of Jupiter, about
71,492 km × 0.669 = 47800 km.
Alternatively, one can start with the ratio of densities, with the ratio of Jupiter’s density to
Saturn’s being (1.33 g/cm
3
)/(0.69 g/cm
3
) = 1.927. For Saturn to have the same density as
Jupiter, it would be 1.927 times the old density. Since Saturn’s mass is assumed to stay the
same, Vnew = Vorginal/1.927. Since V= 4/3r3
, and volume depends on the cube of the radius,
rnew = roriginal/(1.927)1/3
= 0.804 roriginal. Thus, the new radius would be about 80 percent of
Saturn's current radius, or about 60,268 km × 0.804 = 48,500 km. This is 68% of Jupiter’s
radius.
The slightly different answers are the result of rounding and the way that the assumption that
Jupiter and Saturn are perfect spheres (which is not true) affects the individual calculations.
5. Saturn is 8.5 AU from Earth.
d = 8.5 AU × 1.5 × 10
11
m/AU × 1km/1000m= 1.275 × 10
9
km
The rings are 270,000 km in diameter. The angular size formula is
A = (360°)(D)/(2d) = (360°) (270000 km)/( 2 × 1.275 × 10
9
km) = 1.21 × 10
-2
°
At 60 arc minutes per degree, this is 0.67 arc minutes, or 40 arc seconds.
6. Calculate the period of Saturn’s inner and outer rings: a = 90,000 km and 136,000 km.
Saturn’s mass is 5.68 × 10
26
kg.
P2
= 4d3
/(GM)
= 4 (90000 × 1000 m)3
/ (6.67×10
-11
m3
kg-1
s-2
× 5.68×1026
kg)
= 2.418 × 10
8
s2
P = 15,550 s = 4.3 hours
P2
= 4d3
/(GM)
= 4 (136,000 × 1000 m)3
/ (6.67×10
-11
m3
kg-1
s-2
× 5.68×1026
kg)
= 2.62 × 10
9
s2
P = 51,197 s = 14.2 hours
The rings can’t be solid: all parts of a solid object have to have the same period or it would
shear apart.
7. Assume Enceladus is a sphere.
V = 4/3πR3
= 4/3π(499 km/2)3
= 4/3π(499 × 105
cm/2)3
= 6.51 × 1022
cm3
D = M/V = (1.08 × 1023
g) / (6.51 × 1022
cm3
) = 1.66 g/cm3
.

5
The density is 1.66 g/cm3
. This is a higher density than ice, indicating that in addition to icy
materials, Enceladus must have some silicates and possibly even some iron. The rock and/or
iron in Enceladus’ apparent composition may contain some radioactive isotopes that provide
some internal heat in the form of radioactive decay. This could provide the energy to create
tectonic activity on the surface, explaining areas of smooth terrain that apparently have been
(relatively) recently renewed.
10. Use the equation from Chapter 3 to find the surface gravity of Neptune. Insert Neptune’s
mass and radius from the appendix:
M = 1.02 × 10
26
kg. R = 24,764 km
gsurface = GM/R2
= 6.67 × 10
-11
m3
kg-1
s-2
× 1.02 × 10
26
kg / (24,764 km × 10
3
m/km)2
= 11.1 m/s2
This is pretty close to the surface gravity on the surface of the Earth (9.81 m/s2
).
Answers to Test Yourself
1. (c) They are made of hydrogen, helium, and hydrogen-rich compounds.
2. (d) Rock and iron. It is likely to have a “small” core, similar to a terrestrial planet, but
under huge pressure and high temperatures.
3. (d) Inside the Roche limit, tidal stresses will break apart a body that is only held together
by gravity.
4. (e) The source is gravitational energy released by sinking material.
5. (b) The rotation axis has a large tilt.
6. (a) Miranda has a wide variety of difficult-to-explain surface features.
7. (a) A day. All the gas giants have rotation periods less than the Earth’s.

Exploring the Variety of Random
Documents with Different Content

operation. In one variety of this method of unwoolling the skins are
painted on the flesh side with a creamy mixture of lime and water
and piled for a day or two until the pelt is distinctly plumped. They
are then washed with fresh water to remove the excess of lime,
drained, and then enter the tainting stove. By this method the pelts
are obtained in better condition and are less liable to damage by
local excess of putrefaction. In unwoolling the skins are placed over
a beam and the true wool is pulled out by hand. The wool is graded
as it is pulled and different qualities kept separate: ewe wool, lamb
wool, hog wool, etc. The hair is next removed from face and shanks
by means of a blunt "rubbing knife," and the pelt then immersed in
water.
In the other method of depilation, by painting, advantage is taken of
the loose texture of the sheepskin fibre and of the fact that the wool
root is nearly halfway through the skin. The flesh side of the clean
skin is painted with a creamy mixture of lime in a strong solution of
sodium sulphide (14°-24° Beaumé). Care is taken to keep the
depilatant off the wool. The skins are folded flesh to flesh and left
for a few hours or until next day before unwoolling, according to the
strength of the sulphide solution. The depilatory action is entirely
chemical, being due to the solvent action of the sulphide on the hair
root. The lime is sometimes omitted. After pulling, the skins are
opened up and washed in fresh water.
The various classes of wool are sold to the wool-stapler and so to
the woollen industry. As this is a mechanical rather than chemical
industry, its discussion is beyond the scope of this volume. However
unwoolled, the pelt still needs further treatment by the fellmonger. It
needs liming and unhairing. This is done in the ordinary way in pits
of milk of lime, through which the goods pass from old to new limes
in the course of about a week. This plumps the fibres, separates the
fibrils and kills the grease. Paddles are used also to save handling.
Shearlings are sometimes limed 9-14 days and unwoolled without
sweating or painting. After liming the skins are unhaired and fleshed,
and placed in clean strong limes until sold to the tanner.

Sheepskin pelts are sometimes preserved by pickling. This consists
in placing them first in a solution of sulphuric acid (about ¾ per
cent.) together with some common salt. The pelts swell up and
imbibe the acid solution. They are then placed in saturated brine,
which causes a very complete repression of the swelling, the pelts
being apparently leathered. In this condition or partly dried out they
may be kept for years. The forces at work in this phenomenon are
somewhat complex (see Part V., Section I., p. 200). The skins may
be depickled by paddling in a 10 per cent. salt solution to which
weak alkalies such as borax, whitening, carbonate and bicarbonate
of soda, etc., have been added.
The leather manufacturer classifies sheepskins according to the size
of the pelts. The large skins are tanned for light upper leathers and
similar work. These are called "basils." Many large skins are also split
green into "skivers" which after vegetable tannage are finished for
fancy goods, bookbinding, etc. The fleshes are often oil-tanned for
chamois leather (Part IV., Section III., p. 181). Medium-sized skins
such as are obtained from the Down sheep are tanned for "roans,"
and finished as a kind of morocco leather. Small skins are mostly
"tawed" (Part IV., Section I., p. 174) for glove leathers, but some are
made into roller leather by vegetable tannage.
Basils, which represent the heaviest sheepskin work, are tanned and
finished in the following manner. The limed pelts are first bated
lightly at about 80° F. for two days, scudded and drenched. They are
sometimes puered, but more often merely delimed with organic
acids. In this last case they are first paddled in warm water to
remove excess of lime, and a mixture of organic acids is very slowly
added at definite intervals. When nearly free from caustic alkali the
skins are removed and drenched overnight. There are two types of
tannage. The West of England tannage is similar to those noted for
sealskins when oak bark and sumach are employed (Section III., p.
108). There is also the tendency to paddle more and handle less,
and to use the stronger tanning materials such as myrabs, gambier
and other extracts. After about 12 hours' tannage in paddles they

are coloured through, and are then degreased by hydraulic pressure.
The skins are piled in the press with layers of sawdust or bran
between them, and the pressure applied very slowly. Much grease
runs out, for the natural sheepskin contains up to 15 per cent. of oil
and fat. Degreasing may be postponed till tannage is complete, and
the grease can then be extracted by solvents (benzene, acetone,
etc.). Degreasing after part tannage is usually considered preferable,
and the skins may be tanned out in pit or paddle in about a week.
The Scotch tannage is with larch bark from Pinus larix, which
contains up to 13 per cent. of a rather mellow catechol tan. This
material has also some sugars and yields sour and plumping liquors.
The basils are paddled in weak liquors (8°-11°) for about 2 days,
and when struck through are degreased by hydraulic pressure. They
are then soaked back and tanned out in stronger liquors (11°-20°),
which takes up to one week. They are then dried out and sorted in
the crust. The finishing depends of course upon the purpose in view.
If for linings they are soaked, shaved, sumached, struck out well,
nailed on boards and dried right out. They are next stained with a
solution of starch, milk and red dyestuff. After drying they are glazed
by machine and softened with a hand board. For fancy slippers the
crust skins are starched and stained directly, then "staked" (see Part
III., Section II., p. 155), fluffed, seasoned and glazed. If intended for
leggings and gaiters a flesh finish is given. The skins are soaked,
stretched, shaved and sumached. They are then rinsed, drained,
sammed and stained. A brown stain mixed with linseed jelly is usual.
This is spread evenly over the flesh and glassed in. The skins are
dried out, restained if necessary, and staked to raise a nap. Basils for
gaiters are dyed in paddle and fluffed over the emery wheel.
Skivers are split in the limed state and sometimes immediately
degreased. They are next puered at 85° F. for about 3 hours in a
paddle, and scudded. They are drenched at a low temperature
(68°-70° F.), but often 2 or 3 days. They are again scudded and then
rinsed and sent to tan. The skivers are tanned in a few days by
sumach liquors working the goods up from mellow to fresh as usual.
The liquors are warmed. Care must be taken that the goods do not

tear. A great variety of finish is possible, but the "paste grain skiver"
for fancy goods and the plain finish for hat leathers are sufficiently
typical. For paste grains they are soaked and "cleared" for dyeing by
immersion in very weak sulphuric acid, excess of which is carefully
washed out with water. Paddle-dyeing follows, and is preferred to
drum dyeing as the skins are so liable to tear. After being struck out
they are "pasted," by spreading on to the flesh a glue jelly, using
first the hand, then a stiff brush and finally a cloth. The goods are
then dried out. They are then seasoned, partly dried and printed
cross grain. They are next grained two ways lightly; shank to shank,
and across, lightly tooth-rolled and glazed. They are regrained two
ways as before, dried out, and finally softened with a graining board.
They are sometimes sized on the grain to fix the pattern and give a
gloss. For hat leathers the skins are first soaked, sumached and
struck out. If for white or cream finishes they are now lead-
bleached. This consists of pigment dyeing with lead sulphate. They
are immersed alternately in lead acetate and in sulphuric acid
solutions until precipitation is sufficient. They are then dyed to
shade. If for browns it is common to mordant with titanium and use
basic dyestuffs, paddling afterwards in sumach to fix the dye. After
dyeing the goods are struck out again, starched, and dried out on
boards. They are again starched and rolled to give the plain finish.
Roans are not split. They are degreased, puered, scudded and
drenched overnight at 95° F. They are tanned with sumach usually in
pits, and take rather longer than usual to tan. They are finished in
much the same style as goatskins for morocco leather, but as the
sheepskin has little natural grain it needs embossing or printing
according to the type required. If for "hard grains," the skins are
soaked, sumached, seasoned, dried, glazed and damped back for
printing. This is done by the "hard grain" roller, and the goods are
dried out to fix the pattern. They are damped back, sammed, and
grained in four directions (cp. Section II., p. 104), dried out and
boarded to soften. If for straight grains they are printed with a
straight-grain roller, or grained neck to butt. After tooth rolling they

are boarded, dried and glazed. They are softened down and "aired
off" in a cool store.
Roller leather is a special class of sheepskin leather which is used to
cover the rollers used in cotton spinning. The essential requirements
are that a smooth plain finish should be given, and the leather must
not stretch or be greasy. For this purpose small sheepskins with a
fine small grain are chosen, such as those obtained from the Welsh
mountain sheep. The pelts are machine fleshed, short haired and
often puered, but the deliming is also brought about by organic
acids also. The pelts are drenched in pits fitted with paddles, which
are used to stir up the infusion occasionally. A thorough scudding is
given. For the smooth-grain finish it is necessary to tan in weak
liquors, and to give plenty of time so as to ensure complete
penetration. An oak-bark tannage is preferred, but a little extract is
usual to assist. The goods are coloured through in paddle, like basils,
and are then degreased by hydraulic pressure. This should be as
complete as possible, and a little heat is used to assist the escape of
grease. The pressed skins, moreover, must be quite freed from
creases, and this is attained first by paddling in warm water to
remove sawdust, and then by drumming in fairly hot water, in which
they are left overnight. The skins are tanned out in suspenders,
taking about 3 weeks. The crust skins need careful sorting, and are
soaked and hand shaved. They are sumached in drum, rinsed, struck
out, sammed and set. The striking and setting should be thorough,
in order to get rid of stretch. They are next "filled" by coating with
linseed jelly or similar material, and dried out on boards in a
thoroughly stretched condition. They are then trimmed, seasoned
and rolled with a steel roller. They are then staked or perched,
fluffed, re-seasoned, dried and glazed. They are carefully short-
haired, glazed again and finally ironed.
E.I. sheepskins are imported in a tanned condition. These are
soaked back and the turwar bark tannage "stripped" as far as
possible by drumming with soda for 20-30 minutes at 95° F.; after
washing they are "soured" in weak (½ per cent.) sulphuric acid

solution, and retanned with sumach paste for an hour, drumming at
100° F. They may then be finished for basils, moroccos or roller
leather as described above, but are often finished as imitation glacé
kid. In this case they are drum dyed, lightly fat liquored (see Part
III., Section IV., p. 163), struck out and dried. They are staked by
machine, fluffed, seasoned and glazed. They may be re-staked and
reglazed if desired.
REFERENCES.
A. Seymour Jones, "The Sheep and its Skin."
Bennett, "Manufacture of Leather," pp. 30, 85, 107, 208, 349-354,
385.
SECTION V.—CALFSKINS
Calfskins are the raw material for many classes of leather. The term
itself is rather broad. A calfskin may be obtained from a very young
animal and weigh only a very few pounds, or it may be anything just
short of a kip. Goat, seal, and sheep skins are obtained from adult
animals, but calfskins from the young of a large animal. Thus there
are many grades of quality, according to age, and the material must
be chosen with regard to the purpose in view. Some of these
purposes have already been discussed. Heavy calf is treated much
like kip as a curried leather for upper work. Even lighter skins are
given the "waxed calf" and "satin calf" finishes, and make upper

leather of excellent quality. To produce such leathers the treatment
is much the same as described in Part I., Section VIII., p. 76.
Calfskins were also used for very light upper work, in which they
were not so heavily greased in finishing, but rather dyed and
finished as a light leather. In this direction, however, the vegetable
tannage has been almost completely superseded by the mineral
tannages, first by "calf kid," an alumed leather (Part IV., Section I.,
pp. 174-177), and afterwards by the now popular chrome tannage of
"box calf," "willow calf," "glacé calf," "dull calf," etc. (Part III., Section
III., p. 156). In this section, therefore, we have only to consider
calfskins as used to make a vegetable-tanned light leather, such as
may be employed in bookbinding and in the manufacture of fancy
goods. For these purposes the skins receive a mellow liming of 2½-3
weeks. No sulphide need be employed, as the goods are soon fit to
unhair. In such a mellow liming it is important that the bacterial
activity is not too prominent, and hence it becomes advantageous to
work the liming systematically in the form of a round of pits. To
avoid over-plumping in the newest limes some old liquor is used in
making up a new pit, and its bacterial activity is reduced by adding it
to the new caustic lime whilst slaking. Thus for a pack of 200-250
skins, 14-16 stone of lime may be slaked with about 30 gallons of
old lime, and the pit filled up with water. If it be necessary to
shorten the process and to use sulphide, this should be added only
to the tail liquors of the round, and with it should be added, if
possible, some calcium chloride to reduce the harshness of the soda.
The skins should be puered thoroughly to obtain the necessary
softness, bate-shaved if desirable, and drenched with 8 per cent. of
bran overnight.
In tanning for fancy work and for dark colours, the goods are
coloured off and evenly struck through with sumach liquors, and
then tanned further with liquors made from oak bark, myrabolans or
chestnut extract. The methods are very closely similar to those used
for goatskins and sealskins (Part II., Sections II. and III.), and need
not be described in further detail. The tannage is finished off in
sumach. For bookbinding work, however, a pure sumach tannage is

given, using liquor slightly warm (70° F.). Paddle tannages are
common, but for bookbinding the bag or bottle tannage is often
preferred. The skins are sewn together in pairs, grain outwards, and
nearly filled with warm sumach infusion, just as described for
goatskins. They are then handled in old sumach liquors for about 3
days, and piled to drain and press. At this stage the bag is cut open,
the goods worked on the flesh, and the tannage is completed with
separated skins in newer sumach liquors, handling at least once a
day for 4-5 days, as necessary.
In finishing there is the usual variety, but a plain ungrained finish is
most typical, as the smooth and fine grain of the young animal lends
itself to this type of finish better than the skins of goat and seal, and
gives a better quality leather than those from the sheep. The crust
skins are wet back with water at about 110° F., and, if necessary,
sammed and shaved. Sumaching follows, the operation being carried
out in a drum for 1-2 hours. The skins are then well struck out.
Striking and setting should always be thorough for a plain finish, and
this case forms no exception. Dyeing follows next, the paddle being
often preferred to the drum, which is liable to work up a grain. The
dyed skins are placed in cold water for a while and again well struck
out. They are often nailed on boards to samm, and are then set out,
lightly oiled with linseed oil and dried out in a cool shed. Seasoning
follows, with milk and water only. The operation may be done with
either brush or sponge, after which the goods are piled grain to
grain and flesh to flesh to regulate. They may be next perched to
soften and fluffed if desired. After top seasoning with milk, water
and albumin the skins are hung up for a while, piled to regulate and
brushed, first lightly and then more vigorously. They may be then
oiled very lightly and dried out in a cool stove to ensure a soft
leather.
REFERENCE.

Bennett, "Manufacture of Leather," pp. 55, 84, 105, 201, 207, 303.
SECTION VI.—JAPANNED AND ENAMELLED
LEATHERS
The leathers which receive a japanned or enamelled finish are
usually vegetable tannages, and so may be discussed at this stage.
They are popularly known as "patent" leather, but for no obvious
reason. The chief object is to obtain a leather with an exceedingly
bright and permanent gloss or polish, and this is attained by coating
the leather several times with suitable varnishes. The great
difficulties are to prevent the varnish cracking when the leather is
bent or in use, and to prevent it peeling off from the leather. Almost
all classes of vegetable tannage are japanned and enamelled. Hides
are split and enamelled for carriage, motor car and upholstery
leathers, and enamelled calf, seal and sheep skins are used for boot
uppers, toe caps, dress shoes, slippers, ladies' and children's belts,
hat leathers, and so on. Broadly speaking, a japanned leather is a
smooth finish and is usually black, whilst an enamelled leather is a
grain finish with a grain pattern worked up, and more often in
colours. Hence japanned leathers are often made from flesh splits or
leathers with a damaged grain. It is in any case advantageous to
buff the grain lightly, for this permits the varnishes to sink rather
deeper and get a firmer grip, and avoids the too sudden transition
from phase to phase which is one cause of stripping or peeling.
Many flesh splits, however, are printed or embossed to give an

artificial grain and are then enamelled, which tends to fix the
embossed pattern.
Almost any method of preparing dressing hides for upper or bag
work will yield a suitable leather for enamelling and japanning (see
Part I., Section VIII., p. 76; and Section IX., p. 86). If anything the
liming should be somewhat longer and mellower in order to
eliminate grease, as the natural grease of the hide causes the
stripping of some varnishes. In finishing it is important to obtain
even substance, or the varnish is liable to crack. Hides are soaked
and sammed in, and often split. Sometimes they are split twice,
giving grain, middle and flesh, the two former being enamelled and
the last japanned. Other goods are shaved very smooth. The goods
should be next thoroughly scoured and stoned to get as much
"stretch" as possible removed. They are often sumached, washed in
warm water, slicked out again and sammed. They are then lightly
buffed on the grain, and after oiling lightly are thoroughly set out
and dried. Embossing or printing for enamels is done before the
goods are quite dry. Considerable difference of opinion obtains as to
the best oil to use in the above oiling. Linseed oil is widely preferred
as being most likely to agree with varnishes made from linseed oil.
Some manufacturers of japans do not dislike the use of mineral oil,
but strongly object to cod oil, tallow or other stuffing greases as
tending to cause the varnish to strip or peel. Other manufacturers,
on the other hand, will not have leather with mineral oil in it, and
indicate that nothing but cod oil should be used. In all probability
these various preferences are determined by the nature of the
varnish, which differs widely in various parts of the globe.
In this country the varnishes are made largely from linseed oil by
boiling it with "driers." This oil contains much triglyceride of an
unsaturated relative of stearic acid. The double bonds are very
susceptible to oxidation with the production of resinous bodies of
unknown constitution. This phenomenon is known as "drying the
oil," and has been extensively used in the manufacture of linoleums.
The driers are either oxidizing agents or oxygen carriers, such as

litharge, Prussian blue, raw umber, manganese dioxide, manganese
borate, and "resinate." Prussian blue is most preferred for British
japans, as it always materially assists the attainment of the desired
black colour. The exact details of the boiling, and the manufacture of
the varnishes is still largely the trade secret of the master japanners,
and differs indeed for the various stages of japanning. The varnish
for the earlier coats is boiled longer, and the drying carried further,
than in the case of the later coats. This is partly to obtain a product
of such stiffness that it will not penetrate the leather. The driers and
the pigments should be finely powdered and thoroughly mixed in.
The boiling takes several days when at a low temperature, but if
done in 24 hours the temperature may be up to 570° F. In the later
coats driers are often not used, and the product is often mixed with
copal varnish, pyroxylin varnish, etc., which greatly help in obtaining
smoothness and gloss. Turpentine, petroleum spirit and other
solvents are also used to thin the varnishes. Before boiling, the oil is
often purified by a preliminary heating with nitric acid, rose spirit
and other oxidizing agents, which precipitate impurities and thereby
assist in obtaining a bright gloss.
Before the application of the varnishes, the leather is first dried
thoroughly in a stretched condition. This is accomplished by nailing
down on boards which fit like movable shelves into a "stove," a
closed chamber heated by steam pipes. The temperature of the
stove varies widely in different factories, from 140°-200° F.,
according to the nature of the varnishes. The first coat of warm and
rather stiff japan is laid over the hot leather in a warm room, being
spread over first by hand, then by a serrated slicker, and then again
smoothed by hand. The goods are then put into the stove for several
hours to dry. When dry the surface is pumiced and brushed and a
second coat applied in a similar manner, but with increased care.
This is repeated with finer japans until the desired result is obtained.
Brushes are used to apply the later coats. Up to seven coats may be
applied for the production of a smooth japan—three coats of ground
japan, two coats of thinner japan, and two coats of finishing varnish.

After the stoving is complete, the product is given a few days under
ordinary atmospheric conditions to permit the reabsorption of
moisture to the usual extent. Enamelled leathers are then grained to
develop the pattern.
REFERENCE.
Bennett, "Manufacture of Leather," p. 380.
PART III.—CHROME LEATHER
SECTION I.—THE NATURE OF CHROME LEATHERS
In these days the manufacture of chrome leather has attained a
position hardly less in importance than that occupied by the ancient
method of tanning by means of the vegetable tanning materials, and
large quantities of hides and skins are now "chrome-tanned" after
preparatory processes analogous to those described in connection
with vegetable tannages (Part II., Section II.; and Part II., Section
I.).
Chrome leathers are made by tanning pelts with the salts of
chromium, and are typical of what are known as "mineral tannages,"
in which inorganic salts are the tanning agents. Tannage with alum
and salt (see Part IV., Section I.) is one of the earliest mineral

tannages, but is now of relatively minor importance. Chrome tanning
was first investigated by Knapp (1858), who experimented with
chromic chloride made "basic" by adding alkali, but his conclusions
were unfavourable to the process. A patent was taken out later by
Cavallin in which skins were to be tanned by treating with potassium
dichromate and then with ferrous sulphate which reduced the former
to chromic salts, being itself converted into ferric salt. The product,
which was a combination of iron-chrome tannage, did not yield a
satisfactory commercial leather. Another patent, taken out in 1879
by Heinzerling, specified the use of potassium dichromate and alum.
This in effect was a combination chrome-alumina tannage. The alum
had its own tanning action and the dichromate was reduced to
chromic salts by the organic matter of the skin itself and by the
greases employed in dressing. The process, however, was not a
commercial success. In 1881 patents were obtained by Eitner, an
Austrian, whose process was a combination chrome and fat tannage.
The chrome was employed as "basic chromium sulphate" made by
adding common soda to a solution of chrome alum until a salt
corresponding to the formula Cr(OH)SO4 was obtained. Such a
solution is now known to be perfectly satisfactory, but at first it
proved difficult to devise satisfactory finishing processes, and to
supplement the chrome tannage with the fat tannage.
The first undoubted commercial success in chrome tanning was
obtained by the process of Augustas Schultz, whose patent was the
now widely known "two-bath process," in which the skins are treated
successively with a chromic acid solution and with an acidified
solution of "hypo" (sodium thiosulphate). The first bath was made
up commercially of potassium dichromate and hydrochloric acid, so
that, strictly speaking, it contained potassium chloride also. The
second bath contained, in effect, sulphurous acid, which reduced the
chromic acid in the skin fibres to the tanning chrome salts. Free
sulphur is also formed in this bath and in the skin, and contributes to
the characteristic product obtained by this process of tanning. Many
minor deviations from the original process of Schultz have been
introduced, but the main features have been unchanged, and this

method of tanning is widely employed at the present time for both
light and heavy chrome leather. In 1893 tanning by basic chromic
salts was revived and the use of the basic chloride was patented by
Martin Dennis, who offered such a tanning solution for sale. The
validity of the patent has always been doubtful on account of the
previous work of Knapp and others, but the process itself was
commercially satisfactory, and the many variants of this and of the
basic sulphate tannages are now generally known as the "one-bath
process" in contradistinction to the variants of the Schultz process,
and are widely used for all classes of chrome leather. A one-bath
process which deserves special mention was published in 1897 by
Prof. H. R. Procter. In this the tanning liquor was made by reducing
potassium dichromate in the presence of a limited amount of
hydrochloric or sulphuric acid by adding glucose. Although a basic
chrome salt is the chief tanning agent thus produced, there is little
doubt that the organic oxidation products play an essential part in
producing the fullness and mellowness of the leather thus tanned,
but their nature and mode of action has not yet been fully made
clear though lyotrope influence is probable.
More recently Balderston has suggested the suitability of sulphurous
acid as reducing agent. A stream of sulphur dioxide gas is passed
through a solution of sodium dichromate until reduction is complete.
The resulting chrome liquor has been favourably reported upon by
some chrome tanners. Bisulphite of soda has also often been used
as the reducing agent. Other organic substances are also often used,
instead of glucose, to reduce the dichromate.
Theory of Chrome Tannage.—As to the theory of chrome tanning
there is still considerable difference of opinion and much room for
experiment. Some leather chemists regard the tannage as differing
essentially from the vegetable tannages. Mr. J. A. Wilson has even
suggested that the proteid molecule is in time partly hydrolyzed with
the formation of a chromic salt with the acid groups. The author,
however, strongly favours the view that in chrome tanning changes
take place which are closely analogous to those which occur in

vegetable tannage, the differences being mainly of degree. Thus the
hide gel is immersed into a lyophile sol—the chrome liquor—and
there follows lyotrope influence, adsorption, gelation of the tanning
sol, as well as diffusion into the gel, and finally also, probably,
precipitation of the tanning sol at this interface (see pp. 41-47 and
200-219).
In chrome tannage the lyotrope influence is much more prominent
than in vegetable tannage, but the effect is in the same sense, viz.,
to reduce the imbibition of the hide gel. Thus the potassium sulphate
in a chrome alum liquor has its own specific action of this kind and
contributes to the leather formation. Unhydrolyzed chromium
sulphate and the sodium sulphate formed in "making basic" act also
in the same sense.
The tanning sol is probably chromium hydrate, formed by the
hydrolysis of chromium sulphate: it is a lyophile or emulsoid sol and
is in consequence very strongly adsorbed by the hide gel. This
adsorption, involving a concentration of lyophile sol, is the first stage
in gelation, which occupies a relatively more prominent place in
chrome than in vegetable tannage. Some diffusion into the gel also
occurs, and both the gelation and diffusion of the sol are affected by
lyotrope influence, but to a greater extent than in the vegetable
tannage. Thus far the analogy is almost complete.
There remains the question of the precipitation of the tanning colloid
at the interface. This is a point which has not yet been thoroughly
investigated, and which offers considerable difficulty to a clear
understanding, but the matter may be probably summarized thus:
the adsorbed chromium hydrate is precipitated at the interface of gel
and sol to some extent, chiefly through the neutralization of its
charge by the oppositely charged ions of the electrolytes present,
but possibly also—in the last stages of manufacture by the mutual
precipitation of oppositely charged gel and sol.
To illustrate the matter, the case of a basic chrome alum liquor will
be considered. The chromium hydrate sol is primarily a positive sol,

just like ferric and aluminium hydrate sols: i.e. in water they are
somewhat exceptional in that they adsorb H+ rather than OH-. To
cause precipitation therefore it is necessary to make the sol less
positive and more negative. The positive charge of the sol, however,
is greater than in water, because of the free acid formed in the
hydrolysis, which results in the adsorption of more hydrions by the
sol. Hence to ensure precipitation steps must be taken to reduce the
adsorption of hydrions by the chromium hydrate sol. In practice such
steps are taken, and to such an extent that there can be little doubt
that the chrome sol is not far from its isoelectric point. Amongst
these "steps" are (1) making the liquor "basic," i.e. adding alkali to
neutralize much of the free acid, which involves a considerable
reduction in the stabilizing effect of the hydrions; (2) the adsorption
of hydrions by the hide gel when first immersed in approximately
neutral condition; (3) the operation of the "valency rule" that the
predominant ionic effect in discharging is due to the multivalent
anions. In this case the divalent SO4--ions assist materially in
discharging the positive charge on the chrome sol; (4) the final
process of neutralization in which still more alkali is added. The
operation of the valency rule is the most complex of these factors,
for there is also to be considered the stabilizing effect of the kations,
especially of the trivalent kation Cr+++ from the unhydrolyzed
chromium sulphate. It is quite possible also that in the last stages of
chrome tanning there are "zones of non-precipitation" due to the
total effect of multivalent ions, and it is quite conceivable that the
chrome sol may change its sign, i.e. become a negative sol and thus
give also a mutual precipitation with the hide-gel. This is particularly
probable where a local excess of alkali occurs in neutralization.
However that may be, it is probable that most of the tannage is
accomplished by chromium hydrate in acid solution, and it is
therefore legitimate to conclude that adsorption and gelation have a
relatively greater part in chrome tannage. The operation of the
valency rule makes it easy to understand why basic chlorides do not
tan so well as sulphates; the precipitating anion is only monovalent
(Cl-) and chromic chloride contains no substance analogous to the

potassium sulphate of chrome alum and hence contains a less
concentration of the precipitating anion. Hence also the stabilizing
influence of common salt added to a basic alum liquor, the effect
being to replace partially the divalent SO4--by the monovalent Cl-.
Lyotrope influence, however, may be here at work.
It is possible to make out a rather weak case that the tanning sol is
not chromium hydrate at all, but a basic salt of chrome also in
colloidal solution, and to contend that this salt, like most substances,
forms a negative sol, but in practice not negative enough, hence the
desirability of alkali, divalent anions, etc. From this point of view the
analogy with vegetable tannage becomes more complete and the
stabilizing effect of the soda salts of organic acids becomes easy to
understand.
It is highly probable that the electrical properties of the chrome sol
need closer investigation on account of the complexity due to the
prominent effect of multivalent ions. It is desirable to bear in mind
the remarkable phenomenon observed by Burton (Phil. Mag., 1905,
vi, 12, 472), who added various concentrations of aluminium
sulphate to a silver sol (negative). He observed (1) a zone of non-
precipitation due to protection; (2) a zone of precipitation due to the
trivalent kation; (3) a second zone of non-precipitation due to
protection after the sol has passed through the isoelectric point and
become a positive sol; (4) a second zone of precipitation due to the
precipitating effect of the anion on the now positive sol. It seems to
the writer that similar phenomena may possibly occur in chrome
tanning, for whatever the sol actually is, it is not far from the
isoelectric point.
A few observations on the vegetable-chrome combination tannages
will not be out of place at this stage. Wilson refers to the well-known
practical fact that chrome leather can take up about as much
vegetable tan as if it were unchromed pelt, and considers this
evidence that the two tannages are of fundamentally different
nature. "In mineral-tanned leathers the metal is combined with

carboxyl groups, while in vegetable-tanned leather the tannin is
combined with the amino groups. This strongly suggests the
possibility that the two methods of tanning are to some extent
independent of one another, and that a piece of leather tanned by
one method may remain as capable of being tanned by the other
method as though it were still raw pelt" (Collegium (London), 1917,
110-111). To the writer, however, it seems that the facts are
evidence for the contrary proposition, that the tannages are
fundamentally of the same nature. On the adsorption theory, one
would expect chrome leather to adsorb as much tan as pelt; the
readily adsorbable tan is the same, and the chrome leather is an
adsorbent of very much the same order of specific surface as pelt.
The adsorption theory would find it difficult to account for chrome
leather not adsorbing as much tan as pelt. It is quite conceivable
that a chrome leather could adsorb more tan than pelt, owing to the
more complete isolation of the fibrils by the chrome tannage and to
their being coated over by a more adsorbent gel. Adsorption is often
deliberately increased by a preparatory adsorption. Thus sumach-
tanned goatskins are wet back from the crust and "retanned" in
sumach before dyeing, to coat the fibres with a fresh and more
adsorbent gel and so ensure the even and thorough adsorption of
the dyestuff. Mordanting fabrics has a similar object,—the adsorption
of colloidogenic substances which give rise to an adsorbent gel on
the fibre. Unless vegetable-tanned leather is so much loaded with
tan that its specific surface is effectively reduced, one would similarly
expect that vegetable-tanned leather would adsorb the chrome sol.
This, of course, is exactly the case of semi-chrome leather. If, on the
"chemical combination" theory, the vegetable tan combines with the
amino groups and the chrome with carboxyl groups, it is natural to
inquire which groups the dyestuffs combine with. As either tannage
does not interfere with the adsorption of dye, are we to conclude
similarly that tanning and dyeing are fundamentally different
processes?
Those who favour this chemical combination theory, and who offer
equations for the formation of vegetable and of chrome leather,

should likewise suggest an equation for the formation of leather
from pelt by the action of dyestuffs—a practical though hardly an
economic process.
The remarks made earlier in this volume (Part I., Section III.) as to
the occurrence of what have been called "irreversible changes"
subsequent to the mutual precipitation of oppositely charged gel and
sol, are equally applicable to the chrome tannages. Chrome tannage
was once thought to embrace such irreversible changes, but the
process can now be "reversed" with ease. The reversibility of the
chrome tannage is an easier proposition than that of vegetable
tannage, partly because the leather is comparatively much less
tanned, and partly because the acidity or alkalinity of the stripping
agent may be adjusted, as desired, without the oxidation trouble. In
approaching this question from the theoretical side one must
consider mainly whether to solate the tanning agent to a positive or
to a negative sol. Our imperfect knowledge of the electrical forces in
operation in the chrome tannage is thus a serious drawback, but the
evidence on the whole points to the precipitation being effected by a
negative sol near its isoelectric point but in faintly acid solution.
Hence, we should theoretically expect that reversion should take
place into a negative sol in nearly neutral or even faintly alkaline
solution. Thus, suitable stripping agents for chrome leather would be
the alkali salts of organic acids (especially if multivalent). Now,
Procter and Wilson have recently accomplished this stripping of
chrome leather by the use of such salts. They approached the
question from an empirical and practical point of view and found
that Rochelle salt, sodium citrate, and sodium lactate would strip the
chrome tannage with ease. This important and very creditable
achievement will have great practical and commercial importance.
Procter and Wilson have deliberately and carefully refrained from
offering an exact explanation of this reversible action, but point out
that all their stripping agents are salts of hydroxy-acids, and strongly
insist that these form soluble complexes with the chrome. Whilst not
denying this in the least, the present author would point out that
according to the views advanced in this book, the salts of organic

acids which do not contain hydroxyl groups should, when combined
with a monacid base, also strip the chrome tannage. This he has
found to be the case. Thus the chrome tannage is reversible in
solutions of ammonium or potassium oxalate and of ammonium
acetate. With these salts the full effect of multivalent anions is not
attained, so that somewhat strong solutions are necessary. A 10 per
cent. solution of ammonium acetate shows some stripping effect
after a few days, but a 40 per cent. solution after a few hours.
Saturated ammonium oxalate is only a 4.2 per cent. solution, but
shows a stripping effect in 2-3 days. Potassium oxalate (33 per
cent.) shows distinct stripping in 24 hours. Potassium acetate and
sodium acetate show only slight action, because the solution is too
alkaline, but strip if acetic acid be added until litmus is just
reddened. It is noteworthy from a theoretical point of view that a 40
per cent. solution of ammonium acetate is distinctly acid, and indeed
smells of acetic acid. There can be little doubt that such stripping
actions are also connected with the solubility of the stripping agent
in the gel, for the liquid must pass through the walls of the gel to
dilute the liquid in the interior. This view fits in with the facts that
hydroxy acids and ammonium salts are particularly efficient, for the
tendency of chrome to form ammonia-complexes as well as hydroxy
complexes is well known. From this point of view we should not
expect a stripping action from a salt such as disodium phosphate,
which would form an insoluble substance. Actually sodium
phosphate does not strip, and indeed reduces the stripping power of
ammonium acetate. Similarly, we might expect some stripping action
by ammonia and ammonium chloride, with the formation of chrome
ammonia complexes. This actually occurs, a pink solution being
obtained. Sodium sulphite does not strip, possibly partly on account
of its too great alkalinity, but is interesting theoretically to observe
that sodium sulphite as well as Rochelle salt will strip salt stains (see
Yocum's patent, Collegium (London), 1917, 6; also Procter and
Wilson, loc. cit.). This points to the formation of a negative sol, and
suggests many other substances for removing salt stains.

Special Qualities of Chrome Leather.—A few words on the
special peculiarities of the leather formed by chroming will not be
out of place at this stage. One of the greatest disadvantages of the
chrome tannage has been the absence of what is known as the
"crust" or "rough leather" stage. In chrome tanning, the finishing
operations have had to follow on immediately after the tannage.
Chrome leather, after tanning, may be dried out like other leathers,
but if thoroughly dried, or if kept in a dried condition for any time, it
will not "wet back" again with water. Various suggestions have been
made to overcome this difficulty but none yet have found much
favour in practice. The discovery of the reversibility of the tannage,
however, ought to solve this difficulty, and the author would suggest
that any of the substances used for "dechroming" might also be
suitable for "wetting in" chrome leather which has been well dried
out. A piece of chrome leather, dried out well after neutralizing, and
kept in a warm place for four years, wetted back easily in
ammonium acetate, in the author's laboratory.
Another peculiarity of the chrome tannage is that any defects in the
raw material always seem more obvious in chrome than in vegetable
leather. This often necessitates the use of a better quality hide or
skin. Weak grain or loose grain becomes very obvious. The presence
of short hair which both unhairing and scudding have failed to
remove also is usually more evident.
A more serious disadvantage of chrome leather is its tendency to
stretch. In the case of belting leather this feature is an obvious
nuisance, and has inevitably led manufacturers to use powerful
stretching machines upon the goods before they are marketed. In
chrome sole leather also there is a tendency to spread and throw the
boot out of shape.
Further disadvantages arise from the fact that the chrome tannage is
an "empty" tannage. Compared with the vegetable tannage, very
little of the tanning agent is adsorbed. Hence there is little matter of
any kind between the hide fibres isolated during tannage. The
inevitable effect of this is that the leather has not the same solidity

and firmness, and needs filling out with other materials. A
commercial consequence is also that it is impossible to obtain the
same yield of leather from any given quantity of raw material. In
trade parlance chrome tannage does not give good "weight."
Another consequence is that (even when well filled with greases in
finishing) chrome leather tends to be "woolly" on the flesh side or at
cut edges.
On the other hand, chrome tanning has very many advantages over
the older process. The most obvious of these is the great saving in
time. Many chrome tannages involve only a day or two, and none
more than a week or two. A chrome leather factory therefore needs
less capital on account of the quicker turnover. If, moreover, the
market be unfavourable, a chrome tanner can stop or reduce his
output in a very short time, whereas a vegetable tanner is
committed to many weeks' supply of the goods he is manufacturing.
Another notable advantage of chrome leather is its durability. In the
finishing processes more grease is usually employed than in
vegetable tannage, and this has a preservative effect upon leathers
which often get wet. Chrome sole leather and hydraulic leathers are
cases in point. Chrome leather will also stand changes of
temperature and friction much better than vegetable tannages. The
light chrome tannage results, further, in yielding a leather which has
great tensile strength, and it is not surprising to find that chrome
harness and chrome picking bands are highly thought of. The empty
nature of the tannage necessitates the use of stuffing greases, but
such large proportions of these may be used that chrome tannage
becomes obviously suitable if one wishes to produce a waterproof
leather. Hence the popularity of chrome tannage for waterproof
soling and hydraulic leathers.
The advantages of the chrome process are very real, and very
obviously such as will appeal to manufacturers. Chrome leathers
have now been for some time in the forefront as far as boot uppers
are concerned, especially for the best quality goods, in which the
popular "box calf" and "glacé kid" are so largely employed. There

seems little doubt that this will continue to be the case. It is an
unfortunate fact that in this important branch of tanning, British
manufacturers have not quite risen to the occasion. Their products
have in the past been faced with very serious competition from
Continental and American manufacturers of chrome uppers, and
there can be no doubt that these competitors produced a better
article, and produced it more economically. The disorganization of
the Continental factories owing to the war should give British
manufacturers a valuable opportunity of putting such businesses on
a better basis. For sole leather also the chrome tannage makes
constant headway, and the relative proportion of it becomes
gradually greater. A great impetus to chrome sole leather has been
given by the war conditions of Britain. Owing to the submarine
campaigns of Germany the tonnage question became all-important,
and the bulky imports of vegetable tanning materials became a
serious item. British tanners were therefore encouraged to make
more chrome sole and less vegetable sole. The urgent need of
leather for our armies also assisted in the same sense. The
production of chrome sole progressed therefore enormously during
1917 and 1918, and although some reaction will doubtless occur,
there seems little doubt that chrome sole leather has taken a
definite and permanent leap forward. Once the general public fully
appreciate its qualities of waterproofness and durability its future will
be assured.
On the whole the position and prospects of chrome tanning are
good. The chrome tannages are making headway in all directions,
and undoubtedly threaten the existence of many of the older
processes of vegetable tanning.
REFERENCES.
Procter, "Principles of Leather Manufacture," pp. 198-220.
Bennett, "Manufacture of Leather," pp. 210, 355.

Bennett, J.S.L.T.C., 1917, 176.
Stiasny, Collegium, 1908, 117.
SECTION II.—GENERAL METHODS OF CHROME
LEATHER MANUFACTURE
It has been previously pointed out that the chrome tannage is an
"empty" one; the primary principle in the wet work of goods for
chrome leather is to avoid anything which will make this feature
more obvious. In the vegetable tannages relatively larger amounts
of the tanning agents are used, and these fill the interfibrillar
spaces; indeed, as we have seen (Part I., Sections III., V. and VI.),
effort is made to increase these spaces and to fill them to their
maximum capacity, thus yielding a leather of which 50 per cent. is
the tanning agent. In chrome tanning, however, the tanning agent
may only be approximately 5 per cent. of the finished leather, so
that any trouble taken to split the hide fibres or to dissolve hide
substance is usually not only superfluous, but also calculated to
enhance the "emptiness." The governing principle of all the
preparatory processes for chrome tannage is therefore the
conservation of hide substance, and this principle determines the
modifications of the processes of soaking, liming, and deliming,
which are in vogue. Now, in most of these processes there is usually
some loss of hide substance, and it is the particular problem of
chrome tanning to reduce this loss to a minimum in each stage.
Whether the loss of hide substance be due to alkaline or fermentive
hydrolysis, or to solation of the hide gel, the effect is increased by
swelling, and in the wet-work for chrome, therefore, any variations

in the degree of swelling are objectionable. The preparatory
processes should be carried out with as little change as possible in
the volume and elasticity of the pelt. Whether also the loss of hide
be due to hydrolysis or solation, it is increased by time, hence short
processes are (other things being equal) much to be preferred.
Fermentive hydrolysis is minimized by cleanliness, alkaline hydrolysis
by avoiding strongly alkaline liquors, and solation of collagen is
reduced by both, and also by avoiding, as far as possible, the
presence of calcium and ammonium salts.
Soaking should be quick and clean. The use of the paddle or drum
gives the greatest efficiency and also assists in procuring the
softness so essential to the bulk of chrome leathers.
Liming chrome leather satisfactorily is almost an impossible ideal.
Every conceivable arrangement has some objection to it. The time of
the process may be shortened either by the use of sulphide or by
the use of mellow or old limes. To shorten time by the use of sodium
sulphide unfortunately involves the employment of more alkali than
is desirable, with a consequent plumping effect and tendency to
harshness. If sufficient sulphide be used to make the liming very
short, then the grease is not "killed" (saponified or emulsified). If the
harshness and alkalinity be removed by using also an excess of
calcium chloride, then the lyotrope influence of this substance
enhances the solation of the hide gel. On the other hand the use of
old lime liquors avoids the plumping effect, but increases
considerably the bacterial activity, and the bacterial enzymes
produce both hydrolysis and solation of the pelt. In practice what is
generally done is to shorten time by both methods and so to admit
both disadvantages to a limited extent. This is theoretically more
sound than would appear, for in mellow limes sulphide has less
plumping power but is just as strong a depilatant; whilst, on the
other hand, a mellow liming shortened by sulphide is less
objectionable as there is some evidence that bacterial activity is
relatively less in the first few days. Hence a mellow sulphide liming

of 7-10 days is very common in practice, but sometimes a 3-4 days'
process with more sulphide is also found satisfactory.
It would seem probable that the real solution of the problem would
be found by a different process altogether. In this connection it is
interesting to note that a Continental proposal to unhair by enzyme
action only has been found most practicable with goods for chrome,
and, in the author's opinion, some development on these lines, in
which a lipolytic enzyme is used in addition to a proteolytic, might
solve the difficulty, and give a rapid depilation which dispenses with
liming, plumping and deliming with the consequent loss of valuable
hide substance.
In the usual short, mellow, sulphide liming it is clear that there is not
much advantage in a "round" or "set" of pits. Hence the one-pit
system is popular on account of the less labour involved.
The above remarks are less applicable in the case of chrome sole
leather. In this case weight is a great consideration and plumping is
necessary. In such leather the chrome tannage is supplemented by
the use of waxes, which fill up the spaces between the fibres and
give solidity and waterproofness to the finished article. With this
leather an ordinary sole leather liming in sharp liquors is not
unsuitable, handling the goods from "mellow to fresh," but there is,
on the whole, a tendency to shorten the process to about a week by
using more sulphide.
Processes for deliming pelt for chrome leather should also be chosen
by our guiding principle of hide substance conservation. Here again
short processes involving little change in swelling should be
preferred. Now, the ordinary bating and puering processes give (1)
neutralization of lime by organic acids combined with weak bases;
(2) the solation of some hide substance; and (3) a "pulling down"
effect on the swollen pelt. Now, neutralization is quite superfluous,
as the acids of the chrome liquor (one-bath or two-bath) can quite
well accomplish this; the solvent effect is undesirable altogether; and
the "pulling down" effect is also unnecessary if the goods are not

plumped up. With any method of liming, however, some plumping is
obtained, and this creates a problem of practical importance. In the
huge quantities of pelt which go for chrome upper leathers, a
primary consideration is the soft, "kind," or mellow feel of the grain
in the finished leather. This is obtained only by tanning the pelt
when the grain at least is in a thoroughly deplumped and inelastic
condition. It is essential to delime not only so that the alkaline
plumping effect is completely removed, but also so that no acid
plumping effect succeeds it. The practical problem is to decide
whether, in any particular instance, dung puers and bates are
necessary to obtain this result. Bating is clearly not very desirable,
on account of the length of the process, during which hide
substance would be lost unnecessarily, and also because there will
usually be a slight alkaline swelling. Puering with dog-dung infusions
is preferable; it is not such a long process, the liquor is just acid to
phenolphthalein, and the action is more intense, and by puering for
a short time only the loss of hide may be confined to the grain and
flesh only, whilst the desired inelasticity of grain-pelt is soon
obtained. Many large firms have admittedly found themselves unable
to dispense with puering, but others have succeeded in substituting
for it the use of non-swelling deliming and lyotrope agents like
ammonium chloride and boric acid. In all cases it is futile to delime
or puer the grain and then allow the goods to stand until the centre
lime has diffused outwards. The goods must pass into the chrome
liquors when in the correct condition. For heavy chrome leather a
surface deliming with boric acid is all that is necessary. Even that is
superfluous when the goods are to be pickled before tanning.
Types of Two-bath Chrome-Tannage.—Although the original
process of the Schultz patent is quite a practicable one, many
modifications have been introduced. These modifications have been
made to suit the class of goods under treatment, to suit the
particular mode of application which is available or suitable, and to
effect economies of chrome and other material, and of time, and
also to combine with the tannage a pickling effect or a partial alum
tannage. Other modifications arise from the precise acid, neutral, or

alkaline condition of the pelt, being for example obviously necessary
when pickled stock replace neutral pelts. The many two-bath
processes which have been found useful have been classified
previously by the author [6] into three types: (1) The "Schultz type,"
in which such quantities of dichromate and acid are used that there
is no excess of free acid (other than chromic), but an excess of
unaltered dichromate; (2) the "Acid type," in which the chromic acid
is completely free and the liquor contains also some excess of
mineral acid also; and (3) the "Neutral type," in which neither of
these main constituents is in excess, just sufficient mineral acid
having been used to liberate all the chromic acid from the
dichromate.

[6] "Types of Two-bath Chrome Tannage," Leather, 1909, 227-
259.
Now:—
K2Cr2O7 + 2 HCl = 2 KCl + 2 CrO3 + H2O
204 73
Taking the commercial hydrochloric acid as a 30 per cent. solution,
73 parts will be obtained in about 250 parts of commercial acid.
Hence 294 parts dichromate need 250 parts commercial hydrochloric
acid for the above reaction;[7] in other words, 5 per cent.
dichromate needs 4¼ per cent. commercial acid. Similarly 6 per
cent. and 4 per cent. of dichromate need 5.1 per cent. and 3.4 per
cent. respectively of commercial acid. If therefore such quantities be
used we have the so-called "Neutral type" of chroming bath. If less
quantities of acid be used we have the "Schultz type," and if greater
quantities of acid be used we have the "Acid type." The original
Schultz patent used 5 per cent. dichromate and 2½ per cent.
hydrochloric acid, and well exemplifies its type, for there is much
undecomposed dichromate. The composition of some chroming
baths in common use on a practical scale are given below under the
heading of their type:—
Type. Dichromate.
Hydrochloric
Acid.
Salt.
Aluminum
Sulphate.
Schultz 5 2½ — —
5 2½ — 3
5 2½ 5 —

5 2½ 10 —
6 3 — —
Acid
4 4 — —
4 4 5 —
5 5 5 3
5 5 10 —
6 6 15 —
3 3 15 4
2 4 10 —
4 15 24 —
Neutral
5 4¼ 5 —
5 4 — 2½
Chromic acid
5 — 5 —
6 — 8 —
4 — 10 —
[7] Commercial acids of course vary in strength, and the amount
needed varies accordingly.
All the figures are percentages of the weight of pelt. As K2Cr2O7 has
a molecular weight of 294, and Na2Cr2O7 · 2H2O a molecular weight
of 298, in practice they may be considered as interchangeable,
weight for weight. The sodium salt is cheaper and more often used.
The corresponding amount of chromic acid, 2CrO3, has an equivalent
weight of 200, hence any weight of dichromate may in practice be
substituted by two-thirds the weight of commercial chromic acid.
Equivalent weights of commercial sulphuric acid are sometimes used
in place of hydrochloric. The quantity depends upon the strength of
the sulphuric acid used. Aluminium sulphate, Al2(SO4)3 · 18H2O
(mol. wt. 666), may be replaced by ordinary potash alum, K2SO4 ·
Al2(SO4)3 · 24H2O (mol. wt. 948). In practice 7 parts of the former

and 10 parts of the latter may be considered equivalent. It should be
remembered that both these salts are hydrolyzed in solution, and
therefore increase slightly the amount of free acid present. Their
presence decreases the amount of chrome taken up, and as little or
no alumina is found in the leather, there is usually small advantage
in their employment. The use of salt is common but often
unnecessary. It is considered desirable in baths of the acid type to
prevent swelling by the excess of acid, and in baths made up from
commercial chromic acid to replace correspondingly that normally
formed from the reaction of dichromate and acid. It is used also in
all baths which are intended to treat pickled goods. Like all
electrolytes its presence decreases the adsorption of chromic acid.
All these conceivable modifications will make good leather, and the
choice of a process often depends largely upon market prices. On
the whole the tendency is to prefer the neutral or acid type, on
account of the greater ease and completeness with which the bath
may be exhausted. Pickled stock may be depickled before tanning,
by a bath of salt, mixed with borax, whitening, or basic alum
solutions. It may also be placed direct in the chroming bath, but the
amount of acid thus added with the goods must be determined and
allowed for when making up the bath. No allowance is usually
necessary, however, if the "pickle" consist only of alum and salt.
The chroming operation is carried out usually in drums or paddles.
Drums are preferable because more concentrated baths may be
used; these solutions penetrate quicker and are easier to exhaust
economically. They are also preferable for hides and heavy skins.
Paddles are preferable where grain is important, and for light skins in
which little time is needed. Small variations in the ratio of chrome to
pelt, or in concentration of liquor, have little influence upon the
resulting leather.
The analytical investigation and control of chroming baths is usually
simple. A suitable volume of liquor is titrated with N/10 thiosulphate
after acidifying with hydrochloric acid and adding potassium iodide.
The operation should be conducted in a stoppered bottle, and the

liquor allowed to stand for 10-15 minutes after adding the iodide and
before titrating. A little fresh starch infusion should be added
towards the end of the reaction. Each c.c. N/10 thiosulphate
corresponds to 0.0033 gram CrO3 or 0.0049 gram K2Cr2O7. The
same volume of liquor should also be titrated with N/10 caustic soda
and phenolphthalein. Potassium chromate is neutral to this indicator,
i.e. chromic acid acts as a dibasic acid. Any excess of hydrochloric
acid is also titrated. More indicator should be added towards the end
of the titration, as it is often oxidized. Each c.c. N/10 soda
corresponds to 0.005 gram CrO3, 0.01 gram "half-bound" CrO3 (i.e.
present as dichromate), 0.0147 gram K2Cr2O7, or 0.00365 gram HCl.
If a c.c. N/10 thiosulphate and b c.c. N/10 soda be needed the type
of chroming bath may be seen at a glance—
If
The
type is
The bath
contains
b is greater
than ⅓ a but is
less than ⅔ a
Schultz
potassium
dichromate and
chromic acid
b is greater
than ⅔ a
Acid
chromic acid
and free
hydrochloric
acid
b equals ⅓ a Neutral
chromic acid
only
If 10 c.c. chrome liquor require a and b c.c. of thiosulphate and soda
respectively—
I. 10 c.c. of a Schultz bath contain (b-⅓×a) × 0.01 gram CrO3and
{ (a×0.0033)-[(b-⅓×a)×0.01] } × 1.47 grams K2Cr2O7

II. 10 c.c. of an acid bath contain (a×0.0033) grams CrO3 and {(b-
⅔×a)×0.00365} grams HCl
III. 10 c.c. of a neutral bath (a×0.0033) grams
}CrO3
or (b×0.005) grams
The second bath of the two-bath chrome tannage consists of a
solution of sodium thiosulphate acidified with hydrochloric acid. The
reactions in this bath are somewhat complicated, several occurring
simultaneously. Broadly speaking, the final result is due to (1) the
reduction of the chromic acid to a chromic salt by the sulphurous
acid; (2) the formation of a basic chromic salt owing to the excess of
thiosulphate; (3) the reaction of the added acid and thiosulphate to
give free sulphur, which is deposited in and on the leather. The
relative intensity of these effects is variable, according to the
conditions of operation, e.g. the amounts of chemicals used, their
concentration, the nature and condition of the goods, the time of
application, the manner of application, etc. In practice the most
favourable conditions are usually discovered empirically, but, broadly
speaking, the goods are usually added soon after the thiosulphate
and acid are well mixed. There is some evidence that the reduction
is in steps, intermediate products such as sodium tetrathionate and
chromium dioxide are known to be formed. The goods change from
yellow to dark brown, then to green, and finally to the familiar blue.
The sulphur makes the final colour a lighter blue than in the case of
a one-bath tannage, hence the two-bath process is often preferred
for "colours."
On account of the empirical character of this "hypo bath," it is
impossible to fix any exact relation between the quantities of
material used in the chroming bath, and the quantities of "hypo" and
acid used in the reducing bath. The following rules, therefore, must
be understood as rough approximations for practical use, and
though they have been empirically discovered their theoretical
significance is often fairly obvious.

1. The amount of hypo necessary is almost directly proportional to
the amount of dichromate used. In chroming with baths of the acid
or neutral type, the percentage of hypo should be about three times
the percentage of dichromate used. Thus 4 per cent. dichromate
needs 12 per cent. hypo; and 6 per cent. dichromate needs 18 per
cent. hypo on the pelt weight. In baths of the Schultz type a less
proportion of hypo may suffice, but the 10 per cent. hypo for 5 per
cent. dichromate, recommended by the Schultz patent, is generally
considered rather insufficient.
2. The proportion of hypo is increased somewhat for the heavier
classes of goods, and may even reach 20 per cent. of the pelt
weight.
3. An increase in the proportion of hypo is usual with an increase in
the amount of free acid in an acid chroming bath.
4. The percentage of hydrochloric acid in the reducing bath is
roughly half that of the hypo, but is the most variable factor. The
quantity varies with the rate and mode of addition, the class of
goods under treatment, and the composition of the chroming bath.
5. In baths of the Schultz and neutral type it is better to add some
acid to the hypo bath before adding the goods, but this is less
essential for goods from an acid chroming bath.
6. In the case of goods from acid chroming baths, the amount of
acid used in the reducing bath is an inverse function of the excess of
acid in the first bath, e.g. take the following two processes:—
Chroming bath. Hypo bath.
Dichromate.
Hydrochloric
acid.
Hypo.
Hydrochloric
acid.
4 4 12 5
4 15 15 1

Explorations An Introduction to Astronomy 7th Edition Arny Solutions Manual

More Related Content

Similar to Explorations An Introduction to Astronomy 7th Edition Arny Solutions Manual (20)

Recently uploaded (20)

Explorations An Introduction to Astronomy 7th Edition Arny Solutions Manual