110 SOLID FATTY ACIDS. 



atoms of fixed base) dissolve unchanged in from 10 to 20 parts of 

 water ; in a very large quantity of water they become decomposed, 

 an acid salt separating, and the fluid becoming very strongly alka- 

 line ; the alcoholic solution of the acid salt reddens litmus, but on 

 the addition of water to this solution the reddened litmus again 

 becomes blue. The compounds of stearic acid with all other bases 

 are insoluble in water. For stearate of oxide of lipyl (or of glycerin) 

 see " Stearin." 



Preparation. As this acid does not occur in vegetable fats, 

 and exists only in very small quantity in most of the animal fats, 

 except in mutton fat, it is from this last-named source that it is 

 most advantageously prepared ; we obtain it in accordance with the 

 method indicated in our remarks on margaric acid, by boiling with 

 alcohol of 0*83 spec. gray, the fatty acids separated by sulphuric 

 acid from the soap ; this leaves a residue of stearic acid tolerably 

 free from margaric acid ; by repeated solution in absolute alcohol 

 it becomes purified, till we finally obtain a mass possessing the 

 known fusing point of this acid. The following method of pre- 

 paring it may also be recommended. Dissolve saponified mutton 

 fat in 6 parts of warm water, and then wash it well with a large 

 quantity of cold water; a gradual separation of a glistening nacrous 

 mass now ensues, consisting of bistearate and bimargarate of 

 potash. This must be dissolved in 20 times its bulk of hot 

 alcohol, from which, as it cools, the stearate alone separates ; on 

 decomposing this salt with hydrochloric acid, the free acid may be 

 obtained by remelting it in water. 



Tests. An elementary analysis can only be instituted as a 

 test for the presence of stearic acid, when there is a sufficiently 

 large quantity of fat present to admit of the above-mentioned sepa- 

 ration of stearic and margaric acids, a separation which, unfortu- 

 nately, is only practicable when we have very large quantities to 

 deal with. Hence this, the most certain method, is only applicable 

 in determining the amount of stearin in an animal fat. In dealing 

 with smaller quantities we must rest content with the microscopic 

 investigation of the fatty acids separated from hot alcoholic solu- 

 tions. In order to obtain a scale for the approximate ratios of a 

 mixture of margaric and stearic acids, Gottlieb* has determined the 

 fusing points of various mixtures of these acids. His results are 

 as follows : 



* Ann. d. Ch. u. Pharm. Bd. 57, S. 35. 



