FATS. 71 



assigns the formula C^ H, O, or C3 H.^ + 0, and lledtenbachcr 

 Cg H^ 0„+4H0, to tliis substance. At an elevated tempera- 

 ture, a portion of the glycerin is distilled Mdthout change, while 

 the rest is converted into empyreumatic oils, acetic acid, and 

 combustible gases, leaving a carbonaceous residue. 



Diagnosis. Glycerin may be recognized by its taste, by its 

 solubility in water and alcohol, but not in ether, by the absence 

 of crystallization, and by the strong white precipitate which is 

 formed upon the addition of nitrate of mercury. 



/3. Fatty Acids. We shall now proceed to consider the fatty 

 acids, Avhich, in combination with glycerin, constitute the various 

 fats and oils. Two simple fats, stearin and margarin, and a 

 simple oil, olein, with their respective acids, the stearic, margaric, 

 and oleic, are especially deserving of notice. 



The researches of Redtenbacher, Varrentrap, and Bromeis, 

 have shown that the two former of these acids ai'e in reaUty 

 constituents of the same radical, in different stages of oxidation. 

 This radical is termed margaryl, and its constitution is expressed 

 by the formula C,^ H^,,. 



In addition to these acids, we find certain fatty acids in 

 butter, which, in combination with glycerin, form distinct fats. 

 Fremy has likewise described a peculiar acid of this nature as 

 existing in the brain, to which he has given the name cerebric 

 acid. We omit the consideration of various other fatty acids, 

 which are only met with in particular animals and in the vege- 

 table kingdom. 



a. Margaryl and its oxides — stearic and margaric acids. On 

 saponifying mutton-fat with potash, dissolving the soap which 

 is thus formed in six parts of hot water, and then adding 

 forty-five parts of cold water, and allowing the solution to rest 

 at a temperature of 60^, we obtain, after some little time, a 

 lamellar precipitate of bistearate of potash, mixed with bimar- 

 garate, and a little oleate of the same base. On neutralising the 

 free potash in the supernatant fluid with an acid, and proceeding 

 as before, we obtain a precipitate of the margarate and stearate 

 of potash. After this process has been repeated several times, 

 nothing but oleate of potash remains in solution. The preci- 

 pitates must be washed, dried, and dissolved in boiling alcohol. 

 On cooling, the stearate of potash, which is the least soluble, 



