Historic, archived document

Do not assume content reflects current
scientific knowledge, policies, or practices.

: Issued September 5, 1923
Washington, D. C. V Revised March, 1924

WEARING QUALITIES OF SHOE LEATHERS.

By F. P. Verrcn, R. W. Frey, and I. D. CLarxer, Leather and Paper Laboratory,
Bureau of Chemistry.

CONTENTS.

Page. Mare. Page.
Results Of in VeSshigatlone-s ss225c--2 nie o-:

Purpose of investigation............-.-------
Condition of worn leather............-...--

1 =

Plan of investigation: 4
SElECHOMIGMMALChI Al se oss eet ae ae 2

Preparation. of material...-.......-...--.-- 2 fed hens ets ace She Meee Ie. At 7
NWWEAEIn oICONGITIONS=s2e6 os 5-5 Sonac ene. oe ee 3

2

2

PURPOSE OF INVESTIGATION.

There is great need of definite information on the wearing qualities
of leather and on the effect of tannage, grease, loading materials, and
the kind of hide used upon its serviceability and adaptability to the
-many operations to which leather is subjected in making various
articles. Wearers of shoes need such knowledge to enable them to
buy economically; tanners need it to enable them to make high-grade
leather and to use their raw materials to the best advantage and at
the lowest cost. ?

During the World War innumerable questions arose as to which
leathers were best suited to certain purposes and as to what factors
determined their suitability. In practically no case, on either side of
the Atlantic Ocean, could a clear-cut, definite answer be given. The
entrance of the United States into the war offered an excellent oppor-
tunity to conduct on a large scale systematic experiments with shoe
leathers, the Army training camps providing large numbers of men who
lived under fairly uniform conditions.

Accordingly, in July, 1919,2 a very comprehensive study of the
wearing qualities of leather was undertaken by the Bureau of Chem-

1 The wearing experiments herein reported were conducted jointly by the United States Department of
Agriculture and the United States War Department. The leather industry gave valuable cooperation in
preparing leathers and in supplying information on tanning processes. Acknowledgmentismade especially
to Brig. Gen. A. L. Smith, W. D. McKissick, Capt. G.C. Bosson, and Capt. R. L. McAndrews, ofthe War
Department, and to C. P. Keighley and B. A. Corbin & Son Co. for their interest and assistance.

2 The plans for this work were outlined in 1917 and later revised and approved by representatives of the
War Department and ofthe industry.

85513°—24— Bull. 1168——1

y) BULLETIN 1168, U. S. DEPARTMENT OF AGRICULTURE.

istry of the United States Department of Agriculture. This investi-

gation included studies of shoe soles made from the following ma-

terials: (1) Sole leather of typical tannages (oak bark, chestnut

wood, and hemlock bark); (2) sole leather unloaded and loaded

with glucose and epsom salts; (3) rolled and unrolled sole leather;

(4) iow and high oiled sole leather; (5) sole and belting leather; (6)

vegetable-tanned sole leather, chrome-tanned sole leather, and fiber

soles; (7) waxed and unwaxed chrome-tanned sole leather; (8) sole
leather subjected to other treatments of minor importance. Several

types of upper leather and of Army shoes were also included.

PLAN OF INVESTIGATION.
SELECTION OF MATERIAL.

Hides.—In order to secure a reasonable control of the variations
caused by differences in hides, nearly all of the vegetable-tanned sole
leathers were made from green salted hides. A few lots, taken for
comparison, were made from dry hides. Eighteen of the 34 lots of
vegetable-tanned sole leather were made from ‘‘Texas”’ hides, which
were used whenever possible.

Leathers.—All leathers were selected and marked by an experienced
trade man representing the War Department and by representatives
of the Bureau of Chemistry, who also obtained detailed information
on the history of the leathers. Thirty-four lots of vegetable-tanned
sole leather were secured from 19 tanners, 3 lots of vegetable-tanned
belting leather from 3 belting concerns, 2 lots of unwaxed chrome-
tanned sole leather from 2 tanneries, and 6 lots of waxed chrome-
tanned sole leather from 4 tanners. With the exception of 2 broken
lots, each lot of sole leather consisted of 10 bends. At the time these
experiments were planned the question of the best upper leather for
continuous, heavy outdoor service was a very live one. Hence, for
general observations on upper leathers, the chief types of cowhide
upper leathers were included. These consisted of (1) one lot of bark-
tanned leather, flesh finish; (2) two lots of stuffed chrome-tanned
leather, grain finish; (3) one lot of fat-lquored chrome-tanned leather,
grain finish; and (4) four lots of retanned chrome leather, two flesh
finish and two grain finish.

Fiber soles—From the most prominent brands of fiber soles, 96
pairs, representing four makes, were chosen.

PREPARATION OF MATERIAL.

To eliminate as far as possible the difference in wearing quality due
to the section of the hide,’ the soles were taken from only two definite
sections of each bend, one pair at the shoulder end, at a point directly
above the ‘“‘break’”’ in the hide back of the forelegs, and the other
pair at the butt end, directly above the “break”’ in front of the hind
legs. These two sections, representing the extremes of the bend, were
fixed on this physiological basis rather than by a stated measure-
ment from a given point in the bend.

Each lot of leather was given a serial number, the bends of each lot
were numbered from 1 to 10, and each sole was designated by the
number 1, 3, 4, or 6 (Fig. 1). Thus a sole numbered 2-4-1 came from

3 J. Amer. Leather Chem. Assoc. (1918), 12: 86.

WEARING QUALITIES OF SHOE LEATHERS. 3

lot 2, bend 4, position 1. Soles 1 and 3 constituted a pair from the
shoulder end, and soles 4 and 6 a pair from the butt end. The toes
were always pointed toward the head end of the hide and the left sole
was always cut next to the backbone.
_ Piece 2 was cut out between soles 1 and 3, and piece 5 between soles
4 and 6, for use in further developments of machine tests on the wear-
ing quality and other physical properties of leather. These machine
pieces were numbered and marked for direction with a diagonal line
connecting the edge nearer the backbone with that toward the butt.
The trimmings around the soles and test pieces were used to make
up composite samples of the original leather for chemical analysis.
The soles were cut out with a die and permanently stamped with
the complete identification number in the shank on the grain side,
and in the heel and back of the ball on the flesh side. After the soles
had been leveled, the average thickness of the ball of each sole was
recorded in thousandths of an inch. When they had been inspected

Fic. 1.—Identification of soles.

by Army inspectors, the soles were made up into Army shoes by a
New England shoe factory, running on an Army shoe contract. |

The shoes were made according to War Department Specifications
412-2-9, that is, with full double soles on the Munson last, without
hobnaiuls, heelplates, or toeplates. Other types of shoes, from regular
contract delivery, were included, such as specifications 1352 (march-
ing tan, practically identical with 412-2-9, but on a rocker last) and
specifications 1258 (russet dress shoe, single sole and Munson last).

Each shoe was stamped near the top of the quarter with an identifi-
cation number. Altogether there were about 2,000 pairs of shoes.
Of these 967 pairs were soled with the test leathers as follows: 677
pairs with vegetable-tanned sole leathers; 60 pairs with vegetable-
tanned belting leathers; 134 pairs with chrome-tanned sole leathers;
and 96 pairs with fiber.

WEARING CONDITIONS.

It was planned originally to distribute the shoes between a camp
in Ohio, where the climate is comparatively wet, and camps in Texas,
which has a very dry climate. Rapid demobilization at the Ohio
camp, however, necessitated a change, so that most of the shoes upon
which reports were received were worn in Texas and New Mexico.

4 BULLETIN 1168, U. S. DEPARTMENT OF AGRICULTURE.

The shoes were issued only to privates and were carefully fitted by
Army officers. Each private kept a card record of the wear of his
shoes, which was checked from time to time when the shoes were
inspected.

The worn-out shoes were sent to Washington for final inspection.
After the observations and ratings from this inspection had been
recorded, the worn soles were removed in the Bureau of Chemistry
for examination, analysis, and comparison with the original leathers.

RESULTS OF INVESTIGATION.

Because of the frequent changes in officer personnel and the rapid
discharge at the close of the war of soldiers, to many of whom ex-
perimental shoes had been issued, much information was lost. The
results therefore are not as complete as they otherwise would have
been. For this reason it is inadvisable to base detailed conclusions
on this work, or to stress the direct comparison of one lot of leather
with another.

Certain broad, general conclusions, however, appear to be warranted
for the wear conditions of these experiments, especially in view of the
fact that these tests included more shoes, more kinds of leather, and
more comparisons than any other similar experiments

CONDITION OF WORN LEATHER.

All statements concerning upper leathers, types of shoes, and fiber
soles are based on the ratings given in the inspection of the worn
shoes. |

Upper LEATHERS.

At the end of the investigation the upper leathers of all types were
in good condition, only an occasional shoe upper showing material
wear. However, the bark-tanned uppers were decidedly hard and
stiff, 58 per cent being rated as too stiff or hard to wear with comfort
or safety. This condition, while in general agreement with Kuropean
observations in the field, may have been accentuated by the fact that
the experiments were conducted in a section where the soil contains
free alkali and where the climate is very dry.

There was practically no difference between grain-finished stuffed
chrome-tanned and fat-liquored chrome-tanned upper leathers.
These leathers were pliable and retained well their soft dressed feel.
The retanned chrome leather (chrome tanned and slightly retanned
with vegetable tanning materials) seemed to be the best of all in
pliability and softness, but was somewhat dryer or harsher than the
stuffed or fat-liquored chrome-tanned leathers. The grain-finish
retanned chrome leather had a better appearance than the flesh-
finish leather and seemed to be more pliable and mellow. The
upper leathers ranged from 2.3 to 3 millimeters in thickness. Leather
of this weight is too heavy and thick for uppers, except possibly for
winter trench wear or heavy outdoor work.

The experiments were not continued long enough to determine
the actual wearing quality of the upper leathers. It was evident,
however, that, with reasonable care, upper leathers from 2.3 to 3
millimeters thick would outwear three or more soles, and that these
typical American upper leathers were capable of giving long service.

WEARING QUALITIES OF SHOE LEATHERS. 5

The serviceability of such heavy upper leather therefore is of less con-
cern than that of sole leather.

SoLinc MATERIAL.

Fiber soles of the kinds used were not suited for the wear conditions
to which they were subjected, owing to the development of defects,
such as ripping, breaking, and chipping, which, although important
in the consideration of a satisfactory bottom stock, should vere be
distinguished from the property of resistance to the abrasive action of
wear.

Ripping from the stitches was a common fault of the fiber soles,
some lots being worse than others in this respect. Frequently the
soles ripped loose or broke off to the heel or shank when the edge of the
sole wore through the stitches. One lot of fiber soles were stitched
on by a representative of the firm supplying them and the others by a
plant foreman with much factory experience with fiber soles.

Many of the fiber soles of all of the makes bulged—that is, they be-
came larger in area than the middle sole. Small pieces also fre-
quently chipped off from the soles of two lots. :

The results in Table 1, expressed as percentage of the number of
shoes inspected, show clearly the superiority, in the features just dis-
cussed, of the leather soles over the fiber soles used. The data on
fiber soles are given also by individual lots to show that not all of them
developed the defects to the same extent.

TasLE 1.—Proportion of soles that developed imperfections during tests.

or broken| ; - aBRe
- Soling material. ofi to short MP | Bulged.t | eksaiae
heel or ENG _ off
shank. pleces.t

Per cent. | Per cent. | Per cent. | Per cent.
Vegetable-tanned sole leather

maxed and unwaxed chrome-tanned sole leather.............--|......-.-- “LZ APIL ORM Ness ecneeres lege eae Sia
er:
ANATNUGS iS es RS tie em Pet eal ene eh RE eet DB Th 16.1 28.8 8.3
SO TAO ep ret seer erases ame cea oe aise Se Nap eee ae 13.8 2252 ONS U 16.5
Ivar A eee ok Seman s Oe Bo See ete Ne CB: ey ae eae pee eee 4.2 12.5 20.9 20.9
NO LAOS Sree ee teeter reer Aye Benen ey Sle al a af) AN eS 1b i) itil, 49 38 4e ae eee
NOU C4 aera et tet cee tan nd ee ee ie Se ee 59.3 15.6 Pee Wel ier eee, le a

1 Observations on bulging and chipping, of course, could not be made on shoes from which the soles were
entirely ripped or broken.

Because of excessive toe wear and severe conditions of service, any
ripping, chipping, or bulging tendencies were accentuated. It is
probable, therefore, that the percentage of failures for fiber soles would
be decidedly lower for civilian wear, particularly in cities. This
_ point and the possibility that fiber soles, being entirely fabricated
products, might be so modified as to overcome the defects discussed
should be borne in mind, especially since the wear data (p. 8 and fig. 2)
show for the fiber soles which did not come off during the test a very
high degree of resistance to wear, placing them second only to un-
waxed chrome sole leather. |

The fiber soles were backed with a full middle sole of leather.
While not the usual construction, it seems a desirable one, particu-
larly from the standpoint of the comfort of the wearer.

6 BULLETIN 1168, U. S. DEPARTMENT OF AGRICULTURE.

TYPES OF SHOES.

Many of the shoes examined showed excessive toe wear. Many -
were worn through to the middle sole at the tip before the rest of the
soleshowedmuchwear. Whenworn tothis extent, the shoe, of course,
should be repaired, which would mean that the service of most of the
original sole would be lost. Furthermore, most people having such
shoes continue to wear them until they are worn through the middle
sole and welt and sometimes until they are worn down on the uppers at
the toe. This means not only that for some time the feet have not
had proper protection, but that the time, labor, and cost of repair to
shoes so worn would be almost prohibitive and that much leather
would be wasted. Plate I shows excessive toe wear and its conse-
quences.

This is an important matter. Since all the shoes had been carefully
fitted to the soldiers, it is not probable that the excessive wear at the
toe can be ascribed to the fact that the shoes were too short. It
appears rather that this condition, which was far too general to be
attributed to the personal factor, was occasioned by the type or con-

struction of the shoes. This view is supported by the results reported
in Table 2.

TABLE 2.—Toe wear of different types of shoes.

Shoes

Number | showing

ofshoes.| undue
toe wear.

Specifications.

Per cent.
61.5

Specifications 412—2—9 require two full soles on the Munson last;
specifications 1352 are practically the same as 412—2-9, except that
the shoes are made on a slight rocker last; specifications 1258 call for
only one outsole on the Munson last. It is believed that the excessive
toe wear is due to the stiffness of the shoes caused by the double shank
which permits the shoes to bend but little. Thus, in walking the
weight of the body is concentrated at the extreme end of the sole,
instead of being distributed over a greater area at the ball. The
slight rocker effect in specifications 1352 has a tendency to overcome
this, while with specifications 1258 the single sole gives greater flexibil-
ity to the shoe and materially reduces the wearing action at thetoe. It
is understood that the tendency to excessive wear at the toe has been
overcome in the Army shoe by reducing the thickness in the shank
to one sole only, thereby, giving the flexibility previously lacking.

Full double soles, that is double soles in the shank and under the
heel, should be used only with some means of increasing materially
the flexibility of the sole in the shank. Shank stiffness, with conse-
quent rapid wear and waste of leather, also may be partly overcome
by making shoes or boots on a pronounced “‘rocker”’ last. The most
effective construction for securing the protection and service of a
double-sole shoe, however, would seem to be a single-sole shank and
a coal sole at the ball, in other words, a half-sole tap on top of a full
sole.

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Bul. 1168, U. S. Dept. of A

PLATE II.

Bul. 1168, U. S. Dept. of Agriculture.

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WEARING QUALITIES OF SHOE LEATHERS. #4

Burnt SOLES.

That serious damage may be done quickly in drying out wet shoes
is not generally known, and it is difficult to drive home the necessity
of extreme care with wet shoes. Wet leather will certainly burn if
it is placed close to a fire or other source of heat where the heat is
greater than the hand can bear. As the experiments here reported
were conducted mainly under very dry conditions, there were only a
few cases of burnt soles. During the war, however, the Bureau of
Chemistry was frequently called on to confirm the opinions of ex-

erienced Army officers that the condition of a shoe was the result of
Pianing while wet. It is difficult for inexperienced persons to realize
that the fused, vitreous, lustrous, and brittle mass on the bottom
of a shoe is the result of burning wet leather when it was exposed to
heat but little greater than the hand can bear. Plate II, Figure 1,
shows burnt shanks which have lost all the life and properties of good
leather. é

Plate II, Figure 2, shows a shoe (left), in this case with a fiber
outsole, in apparently good condition, with no evidence of having
been mistreated, and the same shoe (right) with the outer sole turned
back to reveal a badly burned, ‘‘fused’’ place in the middle sole.
Cases similar to this, in which even the middle of a leather outsole has
been burned and fused while the outer surface of the sole showed
very few signs of heating, have been observed.

EFFECT OF CERTAIN FACTORS ON WEAR OF SOLE LEATHER.

The wear data for each shoe were tabulated in detail and carefully
analyzed. The data for each sole have been calculated to “days
wear per 9 irons’’ * by proportion from the thickness worn away
and the number of days each pair of shoes was worn. The extreme
wear at the toe was disregarded. Unless a hole was worn through
some other part of the sole before it became necessary to recall the ©
shoes, the thinnest part of the sole was measured and the leather
worn away was determined from the original thickness of the sole.

‘The loss in thickness thus obtained was used in the calculation to

“days wear per 9 irons.”’ Data for the soles from shoes which did
not show appreciable wear were discarded. Averages were taken
from the detailed individual data which are too voluminous to be
included here.

EFFECT OF TANNAGE.

The sole leathers used in these experiments were classified as
‘foak,”’ “hemlock,” and “chestnut,” depending on whether oak
bark, hemlock bark, or chestnut wood extract predominated, making
at least 60 per cent of the tanning formula by which the leathers
were tanned. Only the regular trade brands of leathers are included
in these comparisons. Special leathers are compared on pages 9 to 11.

Oak bark tannages.—Data from 126 soles cut from 7 lots of leather
were summarized. All the hides were short-hair hides. They were
classed as follows: 2 lots of ‘‘Texas’’; 1 lot of ‘butt branded” and
“Texas’’; 1 lot of “‘butt branded’’; 2 lots of ‘‘Colorado’’; and 1 lot
of “small packer.’”’ The number of days the leathers were in the yard

4 The iron, a unit of thickness used by the leather trade, is equivalent to one forty-eighth inch.

8 BULLETIN 1168, U. S. DEPARTMENT OF AGRICULTURE.

being tanned varied from 100 to 185, with an average of 151. The
average days wear per 9 irons varied per lot from 59 to 87. The
average days wear per 9 irons for all lots was 78.1.

Chestnut wood extract tannages.—Data from 175 soles cut from 8
lots of leather were summarized. All the hides were short-hair
hides. They were classed as follows: 6 lots of “‘Texas’’; 1 lot of
“Colorado”’; and 1 lot of “butt branded” and “Colorado.” The
number of days the leathers were in the yard being tanned varied
from 55 to 140, with an average of 92. The average days wear per
9 irons varied per lot from 71 to 97. The average days wear per 9
irons for all lots was 80.

Hemlock bark tannages.—Data from 103 soles cut from 5 lots of
leather were summarized. Three of the lots consisted of short-hair
hides. The hides were classed as follows: 2 lots of ‘‘ Texas”’; 1 lot of
“dry Texas’’; 1 lot of dry ‘Buenos Aires’’; and 1 lot of ‘South
American packer.’’ The number of days the leathers were in the yard
being tanned varied from 85 to 120, with an average of 99. The
average days wear per 9 irons varied per lot from 62 to 102, these
extremes being given by the two dry hide lots. The average days
wear per 9 irons for all lots was 79.3. The average days wear per
9 irons for green salted hides was 78.5.

Oak belting tannages.—Data from 62 soles cut from 3 lots of leather
were summarized. All the hides were “‘native steers.”’ The average
days wear per 9 irons varied per lot from 82 to 88. The average
days wear per 9 irons for all lots was 85.5.

Waxed chrome tannages.—Data from 82 soles cut from 5 lots of
leather were summarized. The hides were classed as follows: 1 lot
of ‘‘Texas’’; 1 lot of ‘‘ Maral bulls’’; 2 lots of ‘‘domestie bulls’’; and
1 lot of “‘dry China buffalo” or “Java.’’ The average days wear
per 9 irons varied per lot from 80 to 118. The average days wear —
per 9 irons for all lots was 102.

Unwazed chrome tannages.—Data from 31 soles cut from 2 lots of
leather were summarized. The hides were classed as “‘ domestic
bulls.” The average days wear per 9 irons was 124 for one lot and
128 for the other. The average days wear per 9 irons for both lots
was 125.8:

Fiber soles.—Data from 81 soles from 4 makes were summarized.
The average days wear per 9 irons varied per lot from 102 to 144.
The average days wear per 9 irons for all makes was 121.6.

Most of the soles were worn in a very dry climate. The percentage
worn in Texas and New Mexico, where there was practically one |
rainfall a month, was as follows: Oak-bark-tanned leathers, 79.5;
chestnut-wood-extract-tanned leathers, 85; hemlock-bark-tanned
leathers, 75; oak-bark-tanned belting leathers, 80.5; waxed chrome-
ee leathers, 69.5; unwaxed chrome-tanned leathers, 80.5; fiber
soles, 63.

There is no appreciable difference in the wear of the four classes
of vegetable-tanned leathers, except that the soles cut from belting
leathers wore a few days longer than those from the other leathers.
Soles from the chrome-tanned leathers wore decidedly longer, those
from the unwaxed chrome-tanned leathers wearing longer than those
from any other tannage. The fiber soles wore well except for the
imperfections previously discussed. =

The results with the three classes of sole leather would seem to
indicate that the time of tanning—that is, the time the leathers were

WEARING QUALITIES OF SHOE LEATHERS. 9

in the tan liquor—is not a material factor in the wear, provided the
leathers have been well tanned. The time of ee nae from an
average of 151 days for oak to 92 days for chestnut, hemlock-tanned
sole leather being intermediate, with an average of 99 days.

Errect oF GLUCOSE AND Epsom SALTS CONTENT.

To study the effect of glucose and epsom salts on the wear of sole
leather several tanners prepared special lots in which the glucose and

epsom salts content differed from that in leather of their regular

tannages, the other factors being kept as constant as possible. A
comparison of the wear of these leathers is made in Table 3.

TaBLE 3.—Effect of glucose and epsom salts content on wear of sole leather.

Composition of original leather (moisture-free basis).

Aver-
\Petro-| Un- age
Lot «4s No. of 4 Com- | days
Description of leathers. leum-} com- | Non- | Water| Ep- S eEideria= y'
No. : soles.| Total! ¢ther| bined | tan- | solu- | som oe sub- pee Riper
ex- | tan- | nins. | bles. | salts.| “°°: |stance.| (7)" | Per
tract.| nin. 7 || OAE
JAP |) JAGR AN IEG Per TeX \\ TGP | Setar |b eke Per
Oak tannage: cent. | cent. | cent. | cent. | cent. | cent. | cent. | cent. | cent.
1 Regular sciccicees 2 LS SAG Shs 14559) | QUOT 27.00) So0t 1260 |} 40525 | 28575 85
2 Special (sameas lot |
1 except lightly |
| rolled and low in |
glucoseandsalts).| 18] .31 | 4.65 | 13.11 | 6.50] 19.61 | .12] .37 | 44.43 | 31.20 75
9 SIO eo ianoocapas 20 | .85 | 1.93 | 11.84 |-15.69 | 27.53 | 2.77.) 7.79-| 40.21 | 30.19 59
8 ReguJar (same as
lot9exceptlowin
glucoseandsalts).| 18] .35 | 1.89 | 13.59 | 6.84 | 20.43 | .12 | 1.11 | 44.66 | 32.89 59
Chestnut tannage:
13 Rerularet = sseceans2 26 SiQa te (8) VIS SO! 12552) 12359) |. 4925553) |-45;:00)8| 29815 82
14 Special (sameas lot
13exceptlowerin
PIUCOSC)fass-ee: o- 22) .70 | 3.85 |. 12.79 | 8.79 | 21.58 | 1.79 | 2.75 | 45.58 | 28.85 72
24 Reoularii eee. e. 28 | 2.50 | 1.79 | 16.56 | 11.94 | 28.50 |1.73 | 4.11 | 44.56 | 24.89 84
25 Special (same as lot
24 except highly
oiled and low in
glucoseandsalts).| 20| .54] 7.48 | 14.54 6.50 | 21.04) .55]| .33 | 45.56 | 25.67 80
Hemlock tannage: ;
29 Reculartsus eae 26 | 2.02 | 2.33 | 14.51 | 14.95 | 29.46 | 4.54 | 6.54 | 39.95 | 28.08 72
30 Special (sameas lot
29 except un-
bleached and low
in -glucose and
US) HBC aes 16 | .36 | 2.62 | 13.85 | 4.68 | 18.53 APATL .22 | 48.41 | 30.32 73
32 Regular eS eaa2s. 18 | 1.59 | 2.20 | 14.47 | 13.87 | 28.34 | 4.15 | 4.82 | 38.86 | 30.21 86
33 Special (sameas lot

32 except low in
glucoseandsalts).| 20] 1.19 | 2.25 } 14.79 | 10.92 | 25.71 | 2.09 | 2.86 | 40.79 | 31.11 73

1 Also contained 1.73 per cent of barium chlorid.

Differences in composition of certain other regular brands of leather .
permit another comparison showing the effect of the glucose and
epsom salts content on wear.

Data secured on 90 soles from 5 lots, consisting of only regular
brands of sole leather having less than a total of 3 per cent of glucose
and epsom salts, were assembled. The total glucose and epsom salts
content varied from 1.23 to 2.99 per cent and averaged 1.95 per cent.
The average days wear per 9 irons for all lots was 80.

Data secured on 249 soles from 12 lots, consisting of only regular
brands of sole leather having more than a total of 7 per cent of glucose
and epsom salts, were assembled. The total glucose and epsom salts
content varied from 7 to 11.08 per cent and averaged 8.92 per cent.
The average days wear per 9 irons for all lots was 80.

Averages from Table 3 alone indicate 8 per cent greater wear for
the loaded leathers. In this same comparison, however, two sets

85513°—24——2

10 BULLETIN 1168, U. S. DEPARTMENT OF AGRICULTURE.

(lots 8 and 9 and lots 29 and 30) having the greatest differences in
glucose and epsom salts content show no significant difference in wear.
In the second comparison, also, no difference in wear is shown.
Considering all results, the indications are that, within the limits
noted, the content of glucose and epsom salts does not materially
affect the wear of soles in a dry climate. Had the tests been con-
ducted in a damper climate, the result might have been quite different.

EFFECT oF RoLtuiInGc LEATHER.

The wearing qualities of rolled leather from regular brands were
compared with those of unrolled leather from the same brands.
The thickness of the rolled leathers was measured after rolling:

TABLE 4.—Effect of rolling on wear of sole leather.

Composition of original leather (moisture-free basis). |
| | 7 _Aver-

|
No 4 Petro. Un- N “Ww | E
: eum- com- | Non- | Water) Ep-
soles. tole ether bined} tan- | solu- | som ace
"| ex- | tan- | nins, | bles. | salts. : 's

Lot Description of leathers.

sub-
tanee.

—————————— SSS EEE —F——— EE

Per |\ Per) Pe; Per Pei her ee erale ee Per

Oak tannage: cent. | cent. | cent. | cent. | cent. | cent. | cent. | cent. | cent.
5 iIRerularesaasne- nee 16 | 1.01 | 2.03 | 16.56 | 9.39 | 25.95 | 1.37 | 1.08 | 40.04 | 31.85 77
6 Sameaslot 5except
unrolled.........- 16) .94/ 2.18 | 14.89 | 8.39 | 23.28 | 1.47 | 1.10 | 40.45 | 33.87 68 ~
Chestnut tannage:
16 Regulars sees eee 20 | 1.14 | 2.75 | 15.77 | 12.29 | 28.06 | 3.19 | 5.03 | 41.23 | 27.84 73
17 Same as lot 16 ex-
E cept unrolled..... 14] .94 | 2.34 | 15.82] 9.30 | 25.16 | 3.28 | 3.13 | 42.21 | 30.19 55
20 Reomlar: jes erere 20 | 1.48 | 2.38 | 13.44 | 16.32 | 29.76 | 3.71 | 6.90 | 44.05 | 23.64 71
21 Same as lot 20 ex-
cept unrolled.....| 24 | 1.63 | 2.56 | 13.35 | 16.35 | 29.70 | 4.02 | 6.28 | 42.50 | 25.11 69

Table 4 shows approximately 16 per cent longer wear for the
rolled leathers per unit thickness of 9 irons. In other words, a well-
rolled leather will outwear the corresponding unrolled leather, thick-
ness for thickness. The results do not mean that rolling a given
piece of leather increases its wear by about 16 per cent. Rolling
compresses the leather. Consequently a given thickness of rolled
leather contains more substance than unrolled leather of the same
thickness, and, other things being equal, it should wear longer. The
decrease in thickness caused by rolling varies in practice. For the
leathers listed in Table 4 the average decrease from rolling was 12.4 per
cent of the average original thickness.

While the expression of wear results on a unit thickness basis does
not take into account the thickness changes resulting from processes
in the tanning and finishing, it is the only feasible method which
permits a comparative summary of data and is in harmony with the
trade practice of buying and selling leather on the ‘‘iron”’ basis.

The wear data of the leathers reported in Table 4 have also been
calculated back to days wear for the actual original thicknesses of the
unrolled and rolled leathers, respectively. On this basis no significant
difference in wear is shown, the average figures being 80.2 days for the
unrolled and 81.2 days for the rolled leathers. This indicates that
rolling does not affect the wear of a piece of sole leather. There is,
however, always the possibility that excessive rollmg may break
down the fiber, thus decreasing the wear resistance of the leather.
Or conditions of service may be such, for example a damp climate,
that rolling increases the wear by imparting to the leather a greater
resistance to the penetration of water.

WEARING QUALITIES OF SHOE LEATHERS. 11

EFFECT OF OILING LEATHER.

As a rule, American sole leathers contain but little oil or grease.
One of the problems on which it was planned to throw some light in
this investigation was the effect on the wearing quality of leather of
materially increasing its oil or grease content.

Table 5 shows the effect on wear of increasing slightly the oil
content in certain leathers.

TABLE 5.—Efect of oiling on wear of sole leather.

Composition of original leather (moisture-free basis).
Aver-
L No. of 12 U aa
Lot ats No.o etro-| Un- ays
No. | Description of leathers. | -oj45, Total] leum-| com- | Non- | Water) Ep- | q),,_| Hide ene wear
ash, |@ther| bined} tan- | solu- | som | 4.4 | Sub- | y.n- | per 9
ery - | tan- | nins. | bles. | salts. * istance ica irons.
tract.| nin.
IGP || Ika || JAG Jap JEEP || JEP | Jeg NN eta Per
| Oak tannage: CONE CONE SCENL. | Cent. |\ Cent. || CEnNL..| Cenk.|| Cent. || cent.
10 Riesularaeeerectnre. 20 | 1.83 | 2.76 | 13.71 | 14.17 | 27.88 | 2.90 | 4.40 | 38.21 | 30.70 87
11 Same as lot 10 ex-
cept not bleached
or drummed and
containing more
QUE See sees salen eee 20 | 1.08 | 4.79 | 14.40 | 10.10 | 24.50 | 1.25 | 1.66 | 39.30 | 31.15 70
Chestnut tannage:

13 Reoulanzese eaeeeee 26) .72 | 1.78 | 11.39 | 12.52 | 23.91 | 1.49 | 5.53 | 45.00 | 29.15 82
15 Same as lot 13 ex-
cept containing

less glucose and :
MOFEION seyss5 22 76 | 4.58 | 18.28 8.60 | 21.88 | 1.75 | 2.47 | 45.34 | 28.08 86

24 Reo umlatest st ee 28 | 2.50 | 1.79 | 16.56 | 11.94 | 28.50 }1.73 | 4.11 | 44.56 24. 89 84
25 Same as lot 24 ex-

eA saaseenasace 20 | .54 | 7. 48 14.54} 6.50 | 21.04] .55 | .33 | 45.56 | 25.67 80

1 Contained also 1.73 per cent of barium chlorid.

The results in Table 5 show very little difference in wear between
a sole leather having the usual oil content and one having a somewhat
higher oil content. Eight per cent greater wear is shown for the
leather having the usual oil content. This might be decidedly differ-
ent if the shoes had been worn in a wetclimate. The difference
between the oil contents of the two classes of leather is not great
enough to warrant.a definite conclusion.

EFFect oF Acip TANNAGE.

In so-called acid tannages the hides are plumped with sulphuric
acid before being tanned or in the rockers, rather than with the
natural organic acids of the tanning materials, as is the case with
nonacid tannages. Comparatively little acid sole leather is now
being made.

Table 6 shows the effect of acid tannage on the wear of chestnut-
tanned leathers.

12 BULLETIN 1168, U. S. DEPARTMENT OF AGRICULTURE.

TaBLE 6.—Effect of acid tannage on wear of sole leather.

Composition of original leather (moisture-free basis).
Aver-
| age
No. of Petro-) Un- : Com- | 42ys
soles. | moaj|leum-| com- | Non- | Water| Ep- | qy,,_| Hide bined wear
ota" ether bined| tan- | solu- | som ane - ae per 9
ex- | tan- | nins. | bles. | salts. “°°: |stance.| (30° irons.

Lot}
No. |

| Description of leathers.
|

tract.) nin.
IDR \\ leap Ieee Per Per | Per | Per | Per Per
| Chestnut tannage: cent. | cent.| cent. | cent. | cent. | cent. | cent.| cent. | cent.
18 | Regular, nonacid... 16 | 2.47 | 1-35 | 15.52 | 14.53 | 30-05 | 3.04 | 4.01 | 41.74 | 26.65 97
19 | Same as lot 18 ex- |
cepizacidaeerre ee 24 | 2.09 | 2.29 | 15.76 | 15.81 | 31.57 | 2.27 | 5.19 | 37.80 | 28.12 82
20 | Regular, nonacid...| 20] 1.48 | 2.38 | 13.44 | 16.32 | 29.76 | 3.71 | 6.90 | 44.05 | 23.64 71
22 | Same as lot 20 ex-
Cepiiacides ese 24 | 1.29 | 1.98 | 18.20 | 14.55 | 32.75 | 2.84 | 6.05 | 38.82 | 26.30 69
|

The results in Table 6 indicate that nonacid-tanned leather wears
slightly longer than leather of an acid tannage. The ratio of com-
bined tannin to hide substance, or the “degree of tannage,” is some-
what higher for the acid-tanned leathers, being 74.4 and 67.8 for the
acid lots 19 and 22 and 63.9 and 53.6 for the nonacid lots 18 and 20.
It is the general opinion of tanners that plumping the hide with sul-
phuric acid hastens the tanning and also causes more tannin to
combine with the hide.

EFFEcT OF PosiTION IN BEND.

The section of the hide from which a sole is cut plays an important
part in the wearing quality of the shoe. In fact, soles cut from differ-
ent sections of.a hide generally show greater differences in wear than
soles cut from the same section of different lots of leather made from
the same class of hides and of the same tannage. Experience has
fully established this fact in a general way, and experiments have
confirmed it on a somewhat comparative basis.> Since the bend rep-
resents the choice section of the hide, it is to be expected that soles
cut from the extreme parts of the bend will not show great variation
in wearing quality. Definite information on how great this differ-
ence is was sought in this investigation.

The average davs wear per 9 irons for all soles from the shoulder
end of the bends is 79 and that from the butt end is 85. Out of 43
Ce compared, the soles cut from the butt section of 25 lots wore

nger.

oe COMPOSITION OF ORIGINAL AND WORN SOLE LEATHERS.

The soles of the worn shoes were removed and thoroughly cleaned
by brushing. For each lot of sole leather composite samples were
made from the ball and from the heel seat of only the well-worn soles.
A strictly comparable composite sample of the original leather was
also made. For the first six lots separate composite samples of the
original leather from the shoulder and also from the butt ends of the
bend were analyzed, as a matter of interest in connection with the
effect of position in the hide upon the composition of the leather.
The official methods of the American Leather Chemists’ Association
were foilowed in making the analyses. The results of these analyses,
calculated to the moisture-free basis, are given in Table 7.

5 J. Amer. Leather Chem. Assoc. (1918), 13; 86.

@:

13

WEARING QUALITIES OF SHOE LEATHERS.

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WEARING QUALITIES OF SHOE LEATHERS. 19
ToTAL AND INSOLUBLE ASH.

The total ash content of the balls of the worn soles is decidedly
higher than that of the original leather; that of the heel seats is ©
but slightly greater.

The soluble ash content of the heel seats of the vegetable-tanned
leathers, with the exception of the lot containing barium chlorid,
imcreased on an average 0.26 per cent and the insoluble ash content
Increased 0.07 per cent, making the gain for total ash equivalent to
0.33 per cent. Both the soluble and insoluble ash contents are
decidedly higher in the balls of the worn soles, being 1.11 and 1.19
per cent, making the increase for the total ash equivalent to 2.3 per
cent. Only four lots show a loss in total ash for the heel seats,
and this loss is very slight, the greatest being 0.17 per cent. The
balls of the worn soles in no case show a loss in total ash.

Three of the seven lots of chrome-tanned leathers show a slight
increase in the total ash of the heel seats, and four show a slight
decrease, making the average a loss of 0.1 per cent. The balls of the
worn soles of all chrome-tanned lots show an average gain in total
ash of 4.19 per cent, despite the comparatively high ash content of
the original leathers. }

CHROMIUM OXID.

The chromium oxid content of the chrome-tanned leather remains
practically constant, showing a tendency to only a slight decrease in
the worn soles.

PETROLEUM-ETHER EXTRACT.

The petroleum-ether extract results are not as consistent as the
ash results. The grease content of the heel seats and balls of the
worn soles, however, shows a general tendency to increase. There
are indications that the grease content of the worn leather reaches an
equilibrium which may differ for each leather or kind of leather.

The petroleum-ether extract in sole leathers containing 4 per cent
or more shows a consistent tendency to decrease on wearing. ‘This
is particularly noticeable in the case of lot 25 which was highly oiled,
the losses for this lot being 4.02 per cent for heel seats and 4.69 per
cent for balls. Nine of the vegetable-tanned sole leather lots show
loss of grease from the heels seats, and six show a loss from the balls
of the worn soles. The average increase in the petroleum-ether
extract of the 34 lots of sole leather is 0.39 per cent for the heel seats
and 0.53 per cent for the balls. Omitting lot 25, these results become
0.53 and 0.69 per cent.

As compared with the sole leathers, the belting leathers are high in
petroleum-ether extract, and all three lots show a loss in both heel
seats and balls, the average being 1.84 and 3.22 per cent, respectively.
In two lots the loss is slight, and it would seem that it is not entirely
in proportion to the original oil content.

All the waxed chrome-tanned sole leathers show losses in petroleum-
ether extract, the average being 2.16 per cent for the heel seats and
11.10 per cent for the balls. The losses for the heel seats vary from
0.58 to 4.46 per cent and those for the balls from 2.77 to 22.52 per
cent.

The unwaxed chrome-tanned sole leathers show an increase in the
balls of 3.40 and 1.45 per cent, and for one lot an increase of 0.41 per

20 BULLETIN 1168, U. S. DEPARTMENT OF AGRICULTURE.

cent for the heel seats and for the other a loss of 0.19 per cent. The
cause of these increases is unexplained.

Ersom SaAtts.

The epsom salts content is calculated from the total magnesium
resent in dilute-hydrochloric-acid-soluble form in the ash of the
eather and is not limited to the quantity that may have been present

as Magnesium sulphate. |

The epsom salts content of all lots of vegetable-tanned sole leather

shows an average increase in the worn soles of 0.21 per cent for the
heel seats and an average decrease of 0.34 per cent for the balls of
worn soles. The heel seats of 11 lots and the balls of 19 lots show
a loss of epsom salts. The change in epsom salts content corresponds
somewhat to the epsom salts content of the original leather, as is
shown by the results in Table 8. ;

TABLE 8.—Change in epsom salts content after wear.

Number of lots showing
loss in—
Original epsom salts content. Rue of

S.

Heel seats. Balls.

Between—
Qiand:2 per cent Sas es ee ee es eee eee ee eee 16 il 2
2 and 3 per Gents. 2 .a2-.3 sees i ee ote Dees Rae See EEE 5 2 4
Sand'4 percent S22 252: yaks es ae ee ee eee ae 7 3 7
4 per Centiand Over? 225.2 2 Ss acca: 25 sere oe ee ee eee 6 5 6

The epsom salts content of the soles cut from the belting leathers
is interesting in that these leathers were originally almost entirely
free from magnesium. ‘The increase during wear in magnesium, cal-
culated as epsom salts, is nearly 1 per cent on the average. Consider-
ing that the soil in the section where the experiments were conducted
is ‘‘alkali soil,” this increase in magnesium is readily explained.

GLUCOSE.

While an increase in the magnesium content of worn soles might
be expected under certain conditions of wear, a similar increase in the
glucose content could hardly be expected. Yet of 34 lots of vege-
table-tanned sole leather, 23 show a gain in glucose in the heel seats
and 20 show a gain in the balls of the worn soles. The increase in
the heel seats ranges from 0.12 to 1.32 per cent and in the balls from
0.03 to 1.82 per cent. The average shows for the heel seats a gain
of 0.32 per cent and for the balls a loss of 0.05 per cent.

To guard against unduly high glucose results, due to the influence
of magnesium and possibly other salts, many of the glucose deter-
minations were Hee by Low’s volumetric method for determining
the copper in the reduced cuprous oxid. The difference between the
glucose results obtained by the two methods was not sufficient to -
ag for the gain in glucose through contamination of the cuprous
oxid. 3

i

|

mE OS Subang pCliCel bac 2 he seee each A652 ee ecees go beemcewacaese 17

WEARING QUALITIES OF SHOE LEATHERS. 21

TABLE 9.—Change in glucose content after wear.

Number of lots showing

Number of LESS

Original glucose content. Beer

Heel seats.| Balls.

MWOT® Ween Coe” CiMlincooias casecssgaou sesso seeressstoscaacscosaser lt 11 15

Here again the results obtained for the belting leathers are very
interesting, since the leathers mentioned in Table 9 originally con-
tained only traces of glucose. The average gain in glucose for the
heel seats 1s 0.83 per cent and for the balls 1.24 per cent.

These results suggest a change in the leather or in some of its
component parts with age. The most plausible explanation would
seem to be a slow hydrolysis of the tannin and related nontannin
materials, promoted possibly by the alkaline condition of the soils
in the sections of the country where the shoes were worn.

WATER SOLUBLES.

As is to be expected from the review of the epsom salts and glucose
results, the water-soluble materials show a general tendency to
increase in the heel seats and balls of the worn soles (Table 10).

TaBLE 10.—Change in water solubles content after wear.

Number of lots
showing gain

Num- in—
Original water solubles content. ber of
lots. ee
ee
seats, | Balls.
essai mane 2Ospelmcen beyaan sre as ace sae secon Siac o seen sate aelecaacteecsaccec be Seee cmicts 3 3 3
BeuVcensZ0ande zp pPomeenl eee inscs sees Seen to dee neste soe s eee eaaceetelecwss 8 7 7
Bebweans2orandro OpeMcemtime ne meso S2 ne cetine iaeise sence ee deceec sec ccc 17 7 5
Qwisekeaeos

EGR CMRI Us ILCO Me een tele eis als sine cei cena Siege Hace oes si ins Sew a we nie ei 6

The three lots of belting leathers which originally contained less
than 20 per cent of water-soluble material show an increase, aver-
aging 1.89 per cent for the heel seats and 4.78 per cent for the balls
of the worn soles. It seems reasonable to conclude that the increase
in water-soluble materials was due to the absorption by the soles of
salts from the dry alkali soil where the shoes were worn.

UNCOMBINED TANNIN.

The uncombined tannin varies but little between the original and
worn leathers, the differences being almost always within the limits
of analytical error. There is, however, a consistent tendency for
the uncombined tannin content of both the heel seats and balls to be
slightly lower than that in the original leathers.

22 BULLETIN 1168, U. S. DEPARTMENT OF AGRICULTURE.

NONTANNINS.

As would be expected from the increase in glucose and epsom salts,
the nontannins show a tendency to be greater in the worn parts of
the leathers, except in those cases where the original leathers contain
high percentages of nontannins.

HipE SUBSTANCE AND COMBINED TANNIN.

The results from the hide substance and combined tannin deter-
minations also show a general tendency to be lower in both the heel
seats and balls of the worn soles than in the unworn leather. This
would follow from the absorption of soluble materials by the soles.

ACIDITY.

Without exception the acidity is lower in the balls of the worn
soles than in the unworn leather, and in all but 8 out of 37 lots the —
results indicate that the leather was alkaline in reaction after wear.
This is undoubtedly due to the nature of the soil in the region where
the shoes were worn.

SUMMARY.

The experiments reported in this bulletin were conducted in a
region having a very dry climate and “‘alkali” soil. Results obtained
under such conditions may not and in some cases probably will not
hold for leather worn in humid climates. Army types of leather and
shoes, worn under Army service conditions, were used for the tests,
so that the comparisons and conclusions here indicated may not
apply to the ordinary kinds of leather and shoes subjected to civilian
wear. Although the results of these experiments can not be con-
sidered final, they are significant indications which, because of the
large number of samples involved, may be accepted until additional
data are obtained. Wear experiments, while offering the best
opportunity to obtain valuable information, also present many
difficulties, so that final conclusions from a single series of tests are
seldom justifiable.

Upper leathers —From the standpoint of durability, all types of
upper leather were satisfactory when the short life of sole leather is
considered. None of them showed signs of being nearly worn out
at the close of the experiments. Retanned chrome leather was the
best in phability and softness, that with the grain finish being slightly
better than that with the flesh finish. Bark-tanned upper leather
was the least satisfactory in appearance and pliability, 58 per cent
of the uppers made from this leather being rated as too stiff and hard.

Soling materials.—Fiber soles of the kinds used were not suitable
for the conditions of wear, owing principally to the fact that as soon
as the soles had worn down through the stitches they frequently -
ripped or broke off. Imperfections, such as ripping, bulging, chipping,
and breaking, were numerous in the fiber soles. When these failures
did not develop, however, the fiber soles wore well, being rated second -
in wear. Such imperfections were negligible in the leather soles.

Types of shoes.—That certain features-in the construction of the
shoes played an important part in their serviceability is strongly
indicated by the excessive toe wear frequently found during this in-

WEARING QUALITIES OF SHOE LEATHERS. 23

vestigation. Disregarding the possibility of misfitting, it would seem
that a full double sole and double shank of heavy leather are responsi-
ble for the wasteful excessive toe wear. A shoe with such a sole bends
but little and the weight of the body is concentrated at the extreme
end of the sole, instead of being distributed over a greater area at the
ball. Even when a double sole is used on the ball of the foot, the
shank should not be doubled, thus saving leather in making the shoe,
lengthening its period of service, and reducing the cost of repair.
Serviceability of various tannages.—The average wear resistance of
the vegetable-tanned sole leathers, classified according to the predom-
inating tanning material, is practically the same for all three types,
being per 9 irons as follows: Oak bark tannages, 78 days; hemlock
bark tannages, 79 days; and chestnut wood extract tannages, 80
days. Belting leather shows a slightly higher wear resistance,

OAK --- ee wee
HEMLOCK we aes =
CHESTNUT ea2ee =
OAK BELT/NG----
WAXED CHROME --

the average wear per 9 irons being 85.5 days. Waxed curcme-
tanned leather, with 102 days wear, was next in order, while un-
waxed chrome-tanned leather, with an average of 126 days wear, was
best of all. Fibersoles, with an average of 122 days wear, were a good
second, except for the physical failures already discussed. ‘The results
are charted in Figure 2.
ee ees | or [ae el eee ce [eat ihc |
Pl eS ee Se ee as
oe es eS ee ee Ee ee ae ee
=] i Gea ee] ed Se Ga eS a Ee el (
QO 70 20 30 FO 350 60 7O BO 90 100 110 120130
AVERAGE DAYS WEAR FER 9 4/RPONS
Fic. 2.—Summary of wear data on soles.

The longer wear of the chrome-tanned leathers, both unwaxed and
waxed, and of the fiber soles warrants further consideration of these
materials. The results indicate that unwaxed chrome-tanned leather
may be exceptionally serviceable in dry sections of the country. The
influence of the climate in this connection must be emphasized.
Unwaxed chrome-tanned leather is not suited for wear in damp or
wet places, because it is very porous and consequently readily takes
up water. This is the primary reason for the manufacture of waxed
chrome-tanned leather, which is simply chrome-tanned leather im-
pregnated with large quantities of waxes and other materials to make
the leather more water resistant.

Loaded leathers.—Under the conditions of these tests, loading with
glucose and epsom salts does not materially affect the serviceability
of leather. It simply adds to the cost. These findings, however,
might have been quite different had the shoes been worn where the
climate was wet.

Rolled leathers—Approximately 16 per cent greater wear for the
rolled than for the unrolled leathers was shown.

94 BULLETIN 1168, U. S. DEPARTMENT OF AGRICULTURE.

Well-oiled leathers —The results on leather oiled in various ways
are not satisfactory, because the differences in oil contents of the
lots were not sufficiently great. The indications are that the sole
leathers of normal oil contents wear about 8 per cent longer than do
the well-oiled leathers. This indication needs further confirmation
before it can be accepted as final.

Acid tannage.—Leather from the acid tannages did not wear quite
as long as that from the nonacid tannages. For several reasons,
however, this is not regarded as conclusive. aDgs

Section of the bend.—The average wear per 9 irons for soles from
the shoulder end of the bend was 79 days, as against 85 days for those
from the butt end. These indications are in harmony with practical
experience and with other experiments on leathers from the different
sections of the hide. 3

The. vutstanding indications from this investigation, which was
conducted under very dry conditions, are: (1) The superior pliability
of retanned chrome and chrome-tanned upper leathers; (2) the objec-
tionable features of fiber soles and the long wear of those that did not
develop such features; (3) the longer wear, thickness for thickness, of
rolled vegetable-tanned sole leather as compared with that of the
corresponding unrolled leathers; and (4) the strikingly longer wear of
coe sole leathers, especially of the unwaxed chrome-tanned
eather.

WASHINGTON : GOVERNMENT PRINTING OFFICE : 1924