156 The N.Z. Journal of Science and Technology. [Aug. 
The skins are placed in rooms, and are hung by the head. The atmo¬ 
sphere is moist owing to the presence of the somewhat damp sheep-skins, 
and the temperature is maintained by means of heating-appliances at from 
60° to 70° F. A considerable amount of ammonia is evolved in consequence 
of the putrefaction; and this ammonia, acting as a weak alkali, aids the 
loosening of the wool. It is possible to de-wool sheep-skins satisfactorily 
by the action of ammonia without serious putrefaction taking place, and 
several methods based upon the use of ammonia solutions upon sheep¬ 
skins have been applied to the process of depilation. 
In the “ sweating ” process the skins are examined daily, and if it is 
found that the wool can be easily removed at both top and bottom the 
skins are taken out of the rooms. If, however, it is found that the wool 
from the neck is easily removed, but that from the tail is still firmly held 
within the tissues, the skin is rehung by the tail until the tail wool is 
loosened. The whole operation may take finally up to five days. This 
method of depilation is bacterial in character, and research has demon¬ 
strated that certain bacteria associated with the putrefaction of protein 
matter are the active agents which bring about the loosening of the wool- 
fibre and the attendant destruction of the skin-structures. The action 
of these bacteria is not by direct attack, but by the secretion of certain 
digestive substances called enzymes, which liquefy the proteid matter of 
the skin. 
It is because of this breaking-down of the skin-fibre which the “ sweating ” 
process involves that modern practice has sought some other method to 
bring about the loosening of the wool without material destruction to the 
skin. It is now customary, when the skins, after washing, have been 
removed from the hydro-extractor, to paint the flesh side with a mixture 
in water of milk of lime and sodium sulphide. The skins are then folded 
wool side outwards and allowed to remain overnight, and on the following 
day the wool is “ pulled ” and the skin is then known as the “ pelt.” 
The effect of arsenic sulphides and lime, which by reaction form calcium 
sulphydrate, has long been known as a depilatory ; but it is only since 
crystallized sodium sulphide (Na 2 S.9H 2 0) has been introduced into 
commerce—and more recently the solid fused sodium sulphide, containing 
from 60 to 62 per cent. Na 2 S—that sulphides other than those of arsenic 
have been generally adopted in fellmongering. The peculiarity of their 
action is that they do not greatly swell the skin itself, but, when painted 
upon the flesh side, penetrate the skin and merely attack the roots 
of the wool, allowing it to be “ pulled ” without injuring the rest of 
the fibre. 
Various methods of mixing the sodium sulphide with the lime are 
adopted, but they all have for their object the production of a depilatory 
which shall be so thick as not to run off the skin while it is being applied, 
and to contain sufficient water to enable it to work. The amount of sodium 
sulphide employed varies, the action upon the roots of the wool being 
accelerated during the warmer months, and consequently less sulphide is 
then required than during the colder months. Likewise, in the case of 
skins being held over from a Saturday until the following Monday instead 
of overnight, the quantity of sulphide required will be less. 
The active de-woolling agent is the sodium sulphide, and not the lime ; 
calcium sulphydrate is formed, and is the most active, but sodium 
sulphydrate, which is also formed at the same time, is likewise efficient. 
