Soda is sodium carbonate, which is produced commercially in a very pure state in several different forms, the chief being sal soda, which is crystallized sodium carbonate, containing about 37% of actual soda; and soda ash, or calcined soda, which is anhydrous sodium carbonate. The latter is the variety most commonly used.
| 10 | grams soda ash are dissolved in |
| 1 | liter of water at 25°–30° C. |
The skins are immersed for 2–3 hours, after which they are rinsed and treated with
| 10 | grams acetic acid dissolved in |
| 1 | liter of water. |
The skins are again thoroughly washed, and then hydro-extracted.
Killing with Lime
Lime, calcium oxide, forms a white, amorphous, porous substance, which readily takes up water, giving calcium hydroxide, or slaked lime. Only the best grades of lime should be used, as it is very frequently contaminated with calcium carbonate and other inert materials.
| 10 | grams of lime are dissolved in |
| 1 | liter of water. |
The skins are entered, and allowed to remain for a period of time which varies according to the nature of the fur. During the killing, the solution must be agitated, in order to evenly distribute the milk of lime, which has a tendency to settle out. After rinsing, the skins are “soured,” by treating with weak acetic acid solution, then thoroughly washed, and drained.