which, in the present case, only occupied half an hour.

The figures show us that the greatest return is obtained by means of
those tanning substances which are richest in resin. In short, hemlock,
sumac, and pine, which give the greatest return, are those containing
the largest amount of resin. Thus, hemlock bark gives 10.58 per cent.
of it, and sumac leaves 22.7 per cent., besides the tannin which they
contain. We know also that pine bark is very rich in resin. There is,
then, advantage to the tanner, so far as the question of result is
concerned, in using these materials. There is, however, another side to
the question, as the leather thus surcharged with resin is of inferior
quality, generally has a lower commercial value, and is often of a color
but little esteemed.

The percentage of tannin absorbed by the different methods of tannages
appears in the following table:

Hemlock 64.2
Sumac 61.4
Pine 90.8
Quebracho 75.3
Chestnut 85.2
Oak 76.9
Laurel 64.8
Oak, three years in the vat 70.2

The subjoined is a statement of the gelatine and tannin in leather of
different tannages, and also shows the amount of azote or elementary
matter contained in each: