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 Rolling 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. 
Lot 
No, 
Description of leathers. 
Composition of original leather (moisture-free basis). 
No. of 
soles. 
Petro- Un- 
T t jJleum- eom- 
l-S* 1 ether bined 
ex- I tan- 
tract, nin. 
Non- 
tan- 
nins. 
Water Ep- 
solu- som 
1 bles. salts. 
Glu- 
cose. 
Hide 
sub- 
stance. 
Com- 
bined 
tan- 
nin. 
Aver- 
age 
days 
wear 
per 9 
irons. 
Oak tannage: 
Regular 
Same as lot 5 except 
unrolled 
Chestnut tannage: 
Regular 
Same as lot 16 ex- 
cept unrolled 
Regular 
Same as lot 20 ex- 
cept unrolled 
Per 
cent. 
1.01 
.94 
1.14 
.94 
1.48 
1.63 
Per 
cent. 
2.03 
2.18 
2.75 
2.34 
2.38 
2.56 
Per 
cent. 
16.56 
14.89 
15.77 
15.82 
13.44 
13. 35 
Per 
cent. 
9.39 
8.39 
12.29 
9.30 
16.32 
Per 
cent. 
25.95 
23.28 
28.06 
25.16 
29.76 
16.35 29.70 
Per 
cent. 
1.37 
1.47 
3.19 
3.28 
3.71 
4.02 
Per 
cent. 
1.08 
1.10 
5.03 
3.13 
6.90 
Per 
cent. 
40.04 
40.45 
41.23 
42.21 
44.05 
42.50 
Per 
cent. 
31.85 
33.87 
27.84 
30.19 
23.64 
25.11 
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. Kolling 
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 rolling 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. 
