The handbook of soap manufacture

by W. H. Simmons; H. A. Appleton

Alkali (Caustic and Carbonated).

The manufacture of alkali was at one time carried on in conjunction with soap-making, but of late years it has become more general for the soap manufacturer to buy his caustic soda or carbonated alkali from the alkali-maker.

Although there are some alkali-makers who invoice caustic soda and soda ash in terms of actual percentage of sodium oxide (Na₂O), it is the trade custom to buy and sell on what is known as the English degree, which is about 1 per cent. higher than this.

The English degree is a survival of the time when the atomic weight of sodium was believed to be twenty-four instead of twenty-three, and, since the error on 76 per cent. Na₂O due to this amounts to about 1 per cent., may be obtained by adding this figure to the sodium oxide really present.

Caustic soda (sodium hydrate) comes into commerce in a liquid form as 90° Tw. (and even as high as 106° Tw.), and other degrees of dilution, and also in a solid form in various grades as 60°, 70°, 76-77°, 77-78°. These degrees represent the percentage of sodium oxide (Na₂O) present plus the 1 per cent. The highest grade, containing as it does more available caustic soda and less impurities, is much more advantageous in use.

Carbonate of soda or soda ash, 58°, also termed "light ash," and "refined alkali". This is a commercially pure sodium carbonate containing about 0.5 per cent. salt (NaCl). The 58° represents the English degrees and corresponds to 99 per cent. sodium carbonate (Na₂CO₃).

Soda ash, 48°, sometimes called "caustic soda ash," often contains besides carbonate of soda, 4 per cent. caustic soda (sodium hydrate), and 10 per cent. salt (sodium chloride), together with water and impurities.

The 48 degrees refers to the amount of alkali present in terms of sodium oxide (Na₂O), but expressed as English degrees.

Caustic potash (potassium hydrate) is offered as a liquid of 50-52° B. (98-103° Tw.) strength, and also in solid form as 75-80° and 88-92°. The degrees in the latter case refer to the percentage of potassium hydrate (KHO) actually present.

Carbonate of Potash.—The standard for refined carbonate of potash is 90-92 per cent. of actual potassium carbonate (K₂CO₃) present, although it can be obtained testing 95-98 per cent.