Bones contain about 5 per cent. of fat, brownish white in colour, and of an oily consistency. Only fresh bones are adapted for the extraction of fat. They are generally split up lengthways by a hatchet, boiled in water, by means of which the fat is extracted, decantered, and filtered. For purifying bone fat, melt the fat and a small quantity of saltpetre together, and afterwards aid sufficient sulphuric acid to decompose the latter. The mass scums very much, becomes of a light yellow colour, loses its noxious smell, and furnishes a fat well adapted for soaps.
Sperm oil is found in commerce bleached and unbleached, the latter having a brownish appearance and disagreeable odour. It is easily saponified, and the resulting soap is readily soluble in water.
There are two kinds in commerce. The one formed by the process of distillation is only fit for making soft soap, owing to its disagreeable odour, whilst the other, the result of simple pressure, yields soaps of great consistency, whether saponified alone or with an admixture of tallow or other fats. It often contains a small amount of sulphuric acid, hence it ought to be washed with some weak ley before using it.
By the action of hyponitric acid upon oleic acid, a pearly white crystalline substance is obtained of the consistence of tallow, and termed elaidic acid. It has been found equally serviceable to both soap and candle manufacturers.
Of Potassa, Soda, and Caustic Soda. Potassa. - This is called in commerce vegetable alkali, sal tartar, pearl-ash, potash, and hydrated protoxide of potassium. The sal tartar is simply purified pearlash. Potash is derived from certain plants, and especially from forest trees. These are cut down, converted into ashes, and lixiviated. The .liquor thus obtained is evaporated until it is brought to a solid state. This residue is subjected to the heat of a reverbera-tory furnace, for the purpose of drying it completely and freeing it from its sulphur and organic particles. In this state it is sold as pearlash.
Soda is of more importance to the manufacturer of soap than potash, because he could not make hard soap without it. The amount of native soda is gradually decreasing, and inadequate to supply the increasing demand. A small quantity is produced from the incineration of certain plants, but the largest portion now used is acquired from the transformation of salt. The best quality of native soda is generally imported from Spain and the Levant, and known as barilla. It contains from 15 to 30 per cent. of carbonate with a little sulphuret, and is mixed with sulphate and muriate of soda. It is considered superior to the artificial, as the hard soap made with it is found to be less brittle and more plastic.
The method of manufacturing soda ash is based upon the preparation of sulphate of soda from salt, its transformation into crude carbonate of soda, designated black ash, and the purification of the crude soda by lixivia-tion, evaporation, and calcination. The product thus obtained is white ash, or soda ash.
Caustic Soda can be purchased either as a solid or a liquid. In the latter state it is called concentrated ley, and soapmalters find it a copyenient commodity, as it saves them the trouble of preparing it themselves. A certain weight of caustic soda represents a larger amount of soda combining with the fats than the ordinary soda. Both red and white are of equal value, for, when the red caustic soda is dissolved, the colouring matter generally settles at the bottom, and the liquid becomes entirely clear.
To estimate the commercial value of soda ash or potash, or solid caustic soda, it is ne-cessary to ascertain the amount of water they contain, the amount of caustic and carbonated alkali, the foreign substances in them.
One hundred grains of the alkali are heated in an iron capsule over suitable heating apparatus, until all the water is expelled, which may be tested by a plate of cold glass held for a moment over the capsule, when whatever vapour rises from the heated material will be condensed on its surface. After all the water is thus driven off, the loss of weight will indicate the amount of water in every 100 grains of material, and the absolute weight of the dried sample will be the percentage of alkali contained in the crude material; the loss will indicate the percentage of water contained therein.
It is very important to ascertain if there is only caustic alkali or only carbonated alkali, as well as the amount of each. For example, if a potash or soda is only one-third caustic, and two-thirds carbonated alkali, the latter must be changed into the caustic state before it can be used in soapmaking. It is best first to determine the amount of caustic alkali. Concentrated alcohol will only dissolve caustic soda, and not in any way affect the other ingredients always found in commercial potash, soda, or caustic soda. Take 100 grains of commercial soda, reduce them to powder in a glass mortar, put half of it in a flask, with the addition of 1 oz. of alcohol of 95 per cent.; shake all well together, and let stand for a few hours, afterwards transfer the liquid floating on the top carefully into an evaporating capsule of porcelain, and let it quickly evaporate over a lamp, gradually increasing the temperature until nothing more evaporates; when cooled, immediately weigh the capsule to ascertain the actual amount of caustic soda which the sample con-tained. Before the evaporating process is commenced, in order that nothing is lost, a little alcohol should be mixed with the deposit in the flask', and being filtered added to the liquid which had already been transferred.