The results of this investigation show that the amount of moisture which a wool can absorb from the atmosphere depends on several factors.
1. The relative humidity of the atmosphere determines the amount of moisture which a dry wool will absorb, more moisture being absorbed during a period of high relative humidity than when the humidity is low.
2. Pure wool-fibre, of which greasy wool contains from 50 to 70 per cent., and slipe wool about 75 per cent., can absorb from 18 to 20 per cent. of its weight of moisture from the atmosphere. This amount is not sufficient to account for all the moisture absorbed by the dry normal wool-fibre.
3. Natural wool-fat, present in greasy wool in amounts up to nearly 17 per cent., and in slipe wool to about 6 ½ percent., is capable of absorbing about 17 per cent. of its weight of atmospheric moisture.
4. Suint, or wool-perspiration, can absorb from 60 to 67 per cent. of its weight of moisture when exposed to the atmosphere, this matter being very hygroscopic, and is present in greasy wools in amounts up to nearly 13 per cent., and in slipe wools to about 2 per cent.
5. Fatty matter other than natural wool-fat, present in slipe wools to an amount of from two to six times that found in greasy wools, and picked up by the wool from the greasy underside of the skins during the washing process, has a retarding effect on the amount of moisture absorbed.
By thoroughly washing wool, as in the case of slipe wools, not only are the incrustating and adhering matters washed out, and so a less weight of the product obtained, but a further deduction in weight has to be allowed for, because the wool is incapable of absorbing the same amount of moisture from the atmosphere which it could absorb in a greasy state, before the natural fat and suint were partially removed. The amount of moisture which slipe wool can absorb from the atmosphere does not reach the legal standard of 18.25 per cent. allowed.
For permission to publish these results the author desires to thank the Christchurch Meat Company (Limited), in whose chemical laboratory at Islington most of the work in connection with this investigation was carried out.