WEARING QUALITIES OF SHOE LEATHERS. 7 
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- 
Eerienced Army officers that the condition of a shoe was the result of 
urning 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. 
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" 4 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 
"oak," "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 1 1 . 
Oak baric 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 
« The iron, a unit of thickness used by the leather trade, is equivalent to one forty-eighth inoh. 
