12 BULLETIN 1168, U. S. DEPAETMENT OF AGRICULTURE. 
Table 6. — Effect of acid tannage on wear of sole leather-. 
Lot 
No. 
Description of leathers. 
No. of 
soles. 
Composition of original leather (moisture-free basis). 
Total 
ash, 
Petro- 
leum- 
ether 
ex- 
tract. 
Un- 
com- 
bined 
tan- 
nin. 
Non- 
tan- 
nins. 
Water 
solu- 
bles. 
Ep- 
som 
salts. 
Glu- 
Hide 
sub- 
Com- 
bined 
tan- 
nin. 
Aver- 
age 
days 
wear 
per 9 
irons. 
Chestnut tannage: 
Regular, nonacid.. 
Same as lot 18 ex- 
cept acid 
Regular, nonacid.. 
Same as lot 20 ex- 
cept acid 
16 
Per 
cent. 
2.47 
2.09 
1.48 
1.29 
Per 
cent. 
1.35 
2.29 
2.38 
1.98 
Per 
cent. 
15-52 
15.76 
13.44 
18.20 
Per 
cent. 
14.53 
15.81 
16.32 
14.55 
Per 
cent. 
30.05 
31.57 
29.76 
32.75 
Per Per 
cent. cent. 
3.04 4.01 
2.27 
3.71 
2.84 
5.19 
6.90 
.05 
Per 
cent. 
41.74 
37.80 
44.05 
38.82 
Per 
cent. 
26.65 
28.12 
23.64 
26.30 
97 
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. 5 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 days 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 
lots compared, the soles cut from the butt section of 25 lots wore 
longer. 
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 followed 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), IS; S6. 
