Water is an element that exists in all hides, and it is necessary to take it into consideration in the analysis. It is present in perceptible quantity even in dry hides. This water cannot be entirely eradicated without injuring the leather, which will lose in suppleness and appearance. Water should then be considered as one of the elements of leather, but it must be understood that if it exceeds certain limits, say 12 to 14 per cent., it becomes useless and even injurious. Moreover, if there is any excess over the normal quantity, it becomes deceptive and dishonest, as in such a case one sells for hides that which is nothing but water. Supposing that a hide, instead of only 14 per cent., contained 18 per cent. of water, it is evident that in buying 100 pounds of such a hide one would pay for four pounds of water at the rate for which he purchased the hide.
There are, also, some matters soluble in air, which are formed to a large extent from fat arising as much from the hide as from tanning substances. The air dissolves at the same time a certain amount of organic acid and resinous products which the hide has absorbed. After treating with air, alcohol is used, which dissolves principally the coloring matters, tannin which has not become assimilated, bodies analogous to resin, and some extractive substances.
That which remains after these methods have been pursued ought to be regarded as the hide proper, that is to say, as the animal tissue saturated with tannic acid. In this remainder one is able to estimate with close precision that which belongs to the hide. The hide being an elementary tissue of unchangeable form, it is easy, in determining the elementary portion, to find the amount of real hide remaining in the product. With these elements one can arrive at a solution of some of the questions we are discussing.
We give below, according to this method, a table showing the composition of the different leathers exhibited at the Paris Exposition of 1878. They are the results of careful research, and we have based our work upon them:
Matter Soluble Fixed
in Air Tannin
| |
| Matter Solu- |
| ble in Alcohol |
| | |
Moisture | | Gelatine |
--+-- --+-- --+-- --+-- --+--
Steer hide, hemlock tanned (heavy leather) 10.95 4.15 19.77 39.1 26.03
Sheepskins, sumac " (Hungarian) 10.8 10.3 12.1 40.3 26.5
Finished calf, pine bark tanned (Hungarian) 11.2 1.7 7.4 41.6 38.1
Steer hide, quebracho tanned (heavy leather) 11.7 1.6 11.2 43.1 32.4
" " chestnut " " " 13.5 0.29 1.99 45.46 38.76
Finished calfskins,
oak tanned (Chateau Renault) 12.4 0.33 3.59 46.74 36.94
Steer hide, laurel tanned (heavy leather) 12.4 1.05 7.95 47.47 31.13
" " oak tanned after three years in
the vats (heavy leather) 11.45 0.37 3.31 49.85 35.02
The following table shows the amount of leather produced by different tannages of 100 pounds of hides:
Pounds.
Hemlock 255.7
Sumac 248.1
Pine 240.3
Quebracho 232
Chestnut 219.9
Oak 213.9
Laurel 210.6
Oak, lasting three years 206
It is important to mention here the large proportion of resinous matter hemlock-tanned leather contains. This resin is a very beautiful red substance, which communicates its peculiar color to the leather.
We should mention here that in these calculations we assume that the hide is in a perfectly dry state, water being a changeable element which does not allow one to arrive at a precise result.
These figures show the enormous differences resulting from diverse methods of tanning. Hemlock, which threatens to flood the markets of Europe, distinguishes itself above all. The high results attributable to the large proportion of resin that the hide assimilates, explain in part the lowness of its price, which renders it so formidable a competitor. One is also surprised at the large return from sumac-tanned hides when it is remembered in how short a time the tanning was accomplished, which, in the present case, only occupied half an hour.