An introduction to the carbon compounds / by R.H. Adie.

  • Adie, R. H. (Richard Haliburton)
Date:
[1899]
Catalogue details

Licence: Public Domain Mark

Credit: An introduction to the carbon compounds / by R.H. Adie. Source: Wellcome Collection.

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    The white solid differs in composition witli its source. Thus from hard fat and Shea butter its composition is represented by Oi,H,,5COOH, called stearic acid, and from softer fats and Japanese wax the composition is represented by CisHsiCOOH, called palmitic acid. The last two acids are paraffins with a carboxyl group substituted for hydrogen, and the first is an olefine with one pair of trivalent carbon atoms or a double bond. _ 98. The properties of palmitic and stearic acids are so similar that they are generally considered together. They are colourless fatty bodies, melting at 61° and 71°, respec- tively. They are insoluble in water, soluble in alcohol, benzene, etc., and in solutions of alkalies. They combine with bases to foi-m salts, the soaps. The soluble alkali salts are soluble in pure water, but insoluble in salt water. Exp. 48.—Make a solution of soap in water and add to it some salt. The soap comes out of solution in the form of flocks, which rise to the surface. Pilter off some of the flocks and boil them with water; they are soluble in pure water, so that they are not fatty acids. The soaps of the alkaline earths, calcium and magnesium especially, are insoluble in water, and are precipitated by the addition of soap solution to hard water. This precipi- tation is quantitative, and is used for the estimation of hardness of water. Soap solution has a curious effect on the surface tension of fats and oils, so that finely divided particles of fats do not tend to run together in a soapy solution. Such an intimate mixture of fat particles and water is termed an emulsion, and the cleansing properties of soap are due to the formation of an emulsion of any particles of grease by the action of the soapy water. The sodium soaps are harder than the potassium soaps, so that the latter are generally called soft soaps. 99. Since glycerin and fatty acids are prepared by splitting fats by the action of caustic potash, we believe the
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