LARD AND LARD ADULTERATIONS. 



449 



The method of proceeding with nitric acid is as follows : 

 Small test tubes are taken which are filled one third full of the melted 

 fat and an equal volume of the strong nitric acid is added, the test tube 

 closed by a piece of rubber cloth, held firmly down by the thumb, and 

 vigorously shaken for a minute. The tube is then placed in a rack and 

 the oily layer allowed to separate from the acid. The oil being lighter 

 rests upon the top of the acid. The coloration produced is studied in 

 the same manner as has been indicated for sulphuric acid. 



METHOD OF DETERMINING THE RELATIVE PROPORTIONS OF STEARIC 

 AND OLEIC ACIDS IN A MIXTURE OF THE TWO. 



The method proposed by Dalican and Jean rests upon the use of data 

 of temperatures produced by the act of crystallization of the two acids. 

 This point is determined in the manner already described. 



The proportions of the two acids are then calculated from the follow- 

 ing table : 



For mixtures of acids such as are afforded by the sapomfication of 

 compound lards, the table appears to be valueless. Many of the tem- 

 peratures of crystallization of such acids, as can be seen from the tables 

 of analyses, fall below 40. 



Dr. Crampton, to whom I assigned the microscopic examination of 

 the lards and lard compounds, has contributed the following account of 

 the work : 



CRYSTALLIZATION OF FATS. 



Microscopic examination. Probably the first application of the use of the micro- 

 scope for distinguishing between fats derived from different sources was by Husson,* 

 who obtained crystals from beef fat, tallow, lard, oleomargarine, goose fat, butter, 



* Jour, de Pharm, et do Chim., 4" se"rie, vol. 37, p. 100. 



17319 pt. 4 4 



