FATS. 73 



from its combinations ; most of the other acids, hoAvever, de- 

 compose their salts. The alkaline and neutral stearates and 

 margarates are soluble in water; the acid salts (for there are 

 bi- and even quadri-stearates of potash and soda) are not 

 soluble in this fluid, neither are the salts formed Avitli other 

 bases. The stearates of baryta, strontia, and lime are white, 

 insipid, and inodorous powders. The neutral stearates of potash 

 and soda occm' in many of the animal fluids, especially in the bile. 

 We have already observed that most of the fats are formed 

 by a combination of stearic and margaric acids with glycerin. 

 The bisteurate of glycerin, or, as it is usually termed, stearin, 

 is best obtained from mutton suet, either by wasliiug it with 

 ether as long as anything is dissolved, or by mixing up melted 

 suet with six times its volume of ether, and suljjecting the 

 mass, when cold, to strong pressure. In both these processes 

 the olein, which is fluid at the ordinary temperature, is removed, 

 and the stearin remains behind, although seldom in a state of 

 purity. Stearin melts at 144°. It is insoluble in water, and 

 only dissolves in alcohol with the aid of heat. It dissolves 

 very readily in boihng ether ; but, as the ether cools, nearly 

 the whole of the stearin is again precipitated, and at 59° it 

 only retains the one hundred and twenty-fifth part of its Aveight 

 in solution. It is also soluble in the fatty and volatile oils, 

 and in pyroacetic spirit. The stearin, after being melted doAvn, 

 and allowed to reassume its sohd form, appears as a white, 

 semitransparent, uncrystalUne mass, not unlike wax. Acids 

 and bases convert it into stearic acid and glycerin. The for- 

 mula for stearin is C^^., H^^, O^^ ; it is equivalent to 



1 Atom of glycerin . . Cg H^ Oj -i 



2 Atoms of stearic acid . C,g5 H,32 Ojo ?' = Ci40 Hj^, 0,7 

 2 Atoms of water . . H2 Oj -I 



The bimargarate of glycerin, or margarin, is obtained by 

 submitting to spontaneous evaporation the ethereal solution 

 from which the stearin has been separated. The flocculi of 

 margarin that separate themselves must be freed from olein by 

 pressure. Margarin melts at 118°. Its solubility in ether is 

 much greater than that of stearin ; at 74° it is perfectly soluble 

 in 5 parts of ether. It is nearly as soluble in alcohol at the 

 ordinaiy temperatm'e as at the boihng point. In other respects 

 it closely resembles stearin. 



