472 FOODS AND FOOD ADULTERANTS. 



substances entering into the mixture at the temperature used by him as 

 a standard. 



Example. 



Mean specific gravity of pure lard at 35 ............................. 9053=a 



Mean specific gravity of cotton oil at 35 ............................ 9042=& 



Mean specific gravity of stearine .............................. * ..... 9015=c 



Mean specific gravity of the cotton oil and stearine adulterant (calcn- . 



_ 

 lated). 5i.5 



The mean specific gravity s of Armour's was .906. 

 Then 



_ 



9091 .9053"" 

 Whence 



x= 18.42 per cent. 



The mean specific gravity of Fairbank's lards was .9095. This shows 

 a theoretical adulteration of over 100 per cent., or in other words a lard 

 composed wholly of stearines and cotton oil, in which the oil is in slightly 

 greater proportions than those indicated above. The iodine number ob- 

 tained shows that the lard approximates such a composition. 



(5) BY CALCULATION FROM IODINE ABSORPTION. 



The determination of the percentage of iodine absorbed by a mixed 

 lard taken alone can not lead to any just idea of the amount of adulter- 

 ant added. 



In the case of specific gravities the numbers for oleo-stearine and lard 

 stearine are near together, viz, for 35 .900 and .903, respectively. But 

 for iodine numbers the difference is very great. In the three samples 

 of oleo-stearine examined the mean iodine number is 20.73 per cent. In 

 the two samples of lard steariue analyzed it is 47.02 per cent. The 

 mean number for cotton oils is 109.02 per cent., for lard, 02.48 per cent., 

 and for prime steam lard, 62.86 per cent. In a mixture we may find all 

 of these ingredients, and therefore the iodine number of such a mixture 

 may approximate that of a pure lard. 



When the iodine number of a supposed adulterated lard goes above 

 65 per cent, there are gravo reasons for suspectiug an adulteration with 

 cotton oil, but a pure lard made from certain parts of the hog may show 

 even. a higher number. 



If the microscopic examination show the presence of oleo-stearine, 

 and cotton oil be revealed by the silver or gold tests, the complexity of 

 the problem is less confusing. The iodine number may then reveal the 

 approximate quantities of the two adulterants present. 



For example : 



1.5 parts of cotton oil at 109=lt;::.r> 

 1. part of oleo-stearine at 20= 20.0 



2.5 parts =183.5 



1. part = 73.4 per cent. 



