The more usual method is to take milling soap, neutralize it with sodium bicarbonate or a mixture of fatty acids, and, after perfuming, it is aerated by mixing the hot soap with air in a specially designed crutcher.
On the other hand the cooling must not be carried too far, for in this case the crystals of sodium bicarbonate become so fine that the muddy mass is very difficult to filter.
A lotion of sodium bicarbonate is useful to allay itching.
Here a separation takes place between the crystals of sodium bicarbonate and the mother-liquor.
There the reaction mentioned above takes place, and Owing to the concentration of the liquid the sodium bicarbonate formed is to a great extent precipitated in the shape of small crystals, forming with the mother-liquor a thin magma.
By this means, sodium aluminate is formed; it is then extracted with water and precipitated either by sodium bicarbonate or by passing a current of carbon dioxide through the solution.