Theoretical organic chemistry / by Julius B. Cohen.

  • Cohen, Julius B. (Julius Berend), 1859-1935.
Date:
1942
Catalogue details

Licence: In copyright

Credit: Theoretical organic chemistry / by Julius B. Cohen. Source: Wellcome Collection.

    194/636 (page 172)
    CHAP. or milled soap, made from compressed shavings of partially dried soap, generally contains much less water. On the other hand, cheap soaps made from cocoa-nut oil, etc., may contain as much as 80 per cent, of water. The Detergent Action of soap appears to be a purely physical phe¬ nomenon, depending partly on surface tension, i.e. the internal attrac¬ tion of the molecules for those lying near the surface of a liquid, the effect being to contract the surface as much as possible, giving rise to the spheroidal condition, e.g. drops of water in air or suspended oil drops in water. Soap acts in a variety of ways. It causes the surface of the grease particles to be wetted by lowering the surface tension between the soap and grease particles. The lowering of the tension may be shown by allowing drops of oil to pass from the end of a pipette bent in the form of a hook, first into water and then into a soap solution. In the first case the drops escape in the spheroidal form : but in the second case the oil is drawn out into a thin cylindrical shape. The effect is best shown with the aid of a lantern and screen. The soap forms a skin round the particles and so promotes emulsification. The process of emulsification of the grease liberates the dirt particles, which are prevented from adhering to the greasy material by their rapid oscillations (Brownian movement) and from coalescing by the negative charge they receive due to the presence of alkali. They are thus removed in a fine state of division along with the greasy matter with which they were originally surrounded. Wool-grease, or Yorkshire grease, is obtained from the scourings of wool, and contains, in addition to fatty acids, the alcohol cholesterol, (-2511440. It is commonly separated from the washings by “ cracking ” or adding sulphuric acid, which causes the greasy matter to rise to the surface, and it is then skimmed off. A more complete separation is effected by concentrating the wash liquors and then separating the grease by means of a centrifugal extractor. The grease, which is specifically lighter, passes to the centre of the rotating cylinder, whence it flows away. It forms a brown semi¬ solid mass, which gives a colourless emulsion with water, and is used as an ointment, known as lanoline. Butter. Good cows’ butter contains on the average about 90 per cent, of fat, 1 per cent, of curd, 1 per cent, of salt, and 8 per cent, of water. Butter fat consists mainly of stearin, palmitin, and olein, with about 7 per cent, of butyrin, and 2 per cent, of caproin, capryhn, and caprin. The purity of a butter may be roughh determined by saponifying a weighed sample with caustic