246 HALOIDS AND HALOID BASES. 



angles of 67 40 X and 52 40. It melts at +62, solidifies, but 

 does not become crystalline on cooling, is brittle, when dry is not 

 a conductor of galvanic electricity, is insoluble in cold and only 

 slightly soluble in hot alcohol, but dissolves very readily in 

 ether. On dry distillation it yields stearic and margaric acids, and 

 the products of decomposition of glycerine ; on saponifi cation it 

 yields stearic acid and glycerine. 



Margarate of oxide of lipyl, margarin, is white and solid ; it 

 crystallises from alcohol as a flocculent white powder, which under 

 the microscope appears in the form of very delicate and often 

 curved needles, which are so grouped as to radiate from one point 

 as a nucleus, and thus to form a whorl of fine, capillary threads ; 

 it melts at +48, and dissolves slightly in alcohol but readily in hot 

 ether ; it separates from either solution on cooling in nacreous scales, 

 and on saponifi cation yields glycerine and margaric acid. 



Oleate of oxide of lipyl, olein* or elain, is a colourless oil which 

 solidifies at a low temperature, is not a conductor of galvanic 

 electricity, becomes rancid on exposure to the air, is never entirely 

 free from margarin and stearin, and on saponification yields, in 

 addition to glycerine and oleic acid, a much larger quantity of mar- 

 garic acid than can be supposed to be derived from the decompo- 

 sition of the margarin. 



Preparation. The above fats may be obtained in various ways, 

 although seldom in a state of perfect purity, from the fat contained 

 in cellular tissue, by repeated melting and purification with water. 

 Usually we dissolve the fat in boiling alcohol, from which, on 

 cooling, the stearin, and a great part of the margarin, separate 

 in crystalline scales, while the olein is almost the only substance 

 remaining dissolved in the cold alcohol. Margarin is obtained in 

 the greatest purity from the hot alcoholic solution of those fats, 

 which, like human fat and the vegetable fats, contain no stearin ; 

 moreover, by strong pressure between the folds of filtering paper, 

 the olein may be tolerably effectually separated from the stearin 

 and margarin, since, above a certain temperature, it penetrates the 

 paper. Tolerably pure olein may be obtained by digesting a fat 

 with half the quantity of potash required for its complete saponifi- 

 cation ; in this case the stearin and margarin are saponified, while 

 the olein remains unchanged. The corresponding acids may be 

 obtained in a similar way, but in a state of much greater purity. 



Tests. Cases sometimes present themselves in which it is not 

 easy to ascertain whether the substance to be examined contains 

 salts of oxide of lipyl, or the corresponding fatty acids. In dealing 



