The mode of operation was as follows:—On Fridays 30 kilos of Erodin powder was mashed in a wooden vessel in 1600 litres water at 40° C. and inoculated with a sufficient quantity of a pure culture of B. erodiens. The temperature was kept at 35°–40° C. by admission of a little steam first thing in the morning, again at noon, and in the evening, and the liquid so prepared was ready for use on Monday. One wheel or paddle was kept going for the work. To start the operation, 200 litres of stock liquor was put into the wheel, and sufficient water added for the goods to turn freely. The skins previously washed, as described in Chapter I., were paddled until sufficiently “fallen” or “down.”
For the following lots, the liquor was strengthened by the addition of 100 to 140 litres of the stock liquor, the wheel being run off and cleaned out once a week. The general result showed that “high-limed” skins and previously salted skins were more refractory to this bate than to dung.
As in the English system of collecting pelts there are all stages of liming, skins containing from 1.5 to 9 per cent. CaO on the dry skin, it is not surprising that considerable difficulty was experienced in keeping the puering uniform. Skins containing over 3 per cent. CaO on the dry skin, seem to require a real putrefactive action in order to “bring them down” sufficiently, or it may be that their alkalinity is too great to allow the bating enzymes to act properly. It may here be said that if the fibres of skin are actually damaged by excessive action of lime or any other chemical, no subsequent treatment is of avail to remedy the defects.
Shearling pelts were excellent when puered with erodin, a further proof that the alkalinity is of importance, since these pelts do not require so much lime as “old fells” to bring them into proper condition for splitting.
For sheep and calf skins treated from the market condition and consequently containing a uniform amount of lime—2–3 per cent.—the process is quite reliable, and is in practical use on a large scale. Goat skins have been successfully bated with erodin by treating them in a concentrated liquor in a drum,[138] instead of a paddle, the mechanical effect of the drumming enabling the bate to penetrate the hard and compact skin, while the more concentrated solution of the enzymes attacks the so-called “beard,” and renders the skins as supple as sheep skins bated in a paddle.
It may be of interest to give here some of the results of the early trials of erodin in a tabular form, due to the late Franz Kathreiner. They are a further proof of the thoroughness with which he carried out all his work.
Leather, N.F. and Kalochrom. Date of Trial, Nov. 22, 1898.
Remarks.—22 skins of E 47 after 3 hours running had 250 c.c. 70 per cent. lactic acid; they were marked with a hole in the tail; were more fallen than the others.