418 FOODS AND FOOD ADULTERANTS. 



same animal absorbed 52.55 per cent., the foot lard 77.28 per cent, the 

 head lard 85.03 per cent. In the prime steam lards mentioned the va- 

 riation in the percentage of iodine absorbed was from 60.34 to 66.47 per 

 cent., and the mean 62.86 per cent. In pure lards of other kinds the 

 mean was 62.48 per cent. Thus in lards of known purity the amount of . 

 iodine absorbed will indicate the probable part of the animal from which 

 the fat in the lard was derived. The wide variation between the iodine 

 numbers of pure lard and those of the adulterants used in making com- 

 pound lard serve to render this number of the greatest importance in 

 analytical work. 



(/) The reaction with nitrate of silver. Pure lards, treated with a solu- 

 tion of nitrate of silver, after the method of Bechi,or the fatty acids 

 thereof, after the method of Milliau, give no reduction of metallic .silver, 

 or, at most, only a trace and no or only a slight coloration. This fact is 

 of *the utmost importance in the analysis of lard. 



(g) Microscopical appearances. Lard, examined with the microscope, 

 shows a definite crystalline structure, but does not plainly reveal the 

 character of the crystals. When lard is slowly crystallized from ether, 

 beautiful rhombic crystals of stearine are obtained, which are easily 

 distinguished from the groups of fan shaped crystals given by beef or 

 Siutton fat under similar conditions. 



(h) Moisture in lard. The quantity of water in pure lard varies from 

 a mere trace to .7 per cent. Twelve determinations showed the follow- 

 ing per cents. : 



.7 .4 .2 .5 .6 .5 

 .2 .2 .* .3 .3 .7 



(5) PROPERTIES OF LARD ADULTERANTS. 



COTTONSEED OIL. 

 A. PHYSICAL PROPERTIES. 



(a) Specific gravit y. Cottonseed oil being liquid at ordinary temper- 

 atures, its specific gravity can be easily taken at the temperature of 

 the room. For purposes of comparison, the rate of variation in the 

 specific gravity of the oil can be determined and its specific gravity at 

 any given temperature calculated, or its specific gravity can be directly 

 determined at 35, 40, or 100, as may be desired, by comparison with 

 water at the same temperature. In the samples examined the sprrilic 

 gravities of the oils at 35 vary from .9132 to .9154. The mean for nine 

 teen samples^is .9142. These numbers show the relative weight of the 

 oil, an equal volume of water at the same temperature being taken as 

 unity. 



