474 POODS AND FOOD ADULTERANTS. 



In general it appears that two parts of stearine would neutralize the 

 effect of one part of cotton oil. A mixture of 1.5 parts of cotton oil and 

 1 part of mixed steariues would have the following theroretical index : 



1.5 parts cotton oil at 1.4674 =2.2011 

 1 part stearines at 1.4588 = 1.4588 



2.5 parts =3.6599 



Ipart =1.4640 



For a lard adulterated with the above-mixed adulterant we may use 

 the following formulae : 



Let r=observed index at 25 

 <i =index at 25 of lard. 

 fc=index at 25 of cotton oil. 

 c= index at 25 of stearine. 



'25 =iudex at 25 of the mixed cotton oil and stearine. 



x= per cent, of adulteration. 

 Then 



_ 

 



1.5 b+c 



a. 



2.5 



As an illustration of this formula take the mean numbers obtained 

 in the tables of samples for lard, cotton oil, stearines, and Armour's 

 mixtures : 



Mean index of Armour's samples r = 1.4634 

 Mean index of pure lards a= 1.4620 



Mean index of cotton oils 6=1.4674 



Mean index of steariues c= 1.4588 



Value of L5ft + =1.4640 

 2.5 



Then #=.14 -=-.0020 =70 percent. 



According to this formula Armour's samples would have only 30 per 

 cent, of pure lard, a result which is contradicted by other data. 1 am 

 inclined to believe that the examination of a larger number of samples 

 of stearine may show a higher index and thus bring the results obtained 

 by the application of the above formula more into harmony with the 

 other data. 



The index for the Fairbank samples, 1.4651, shows that in these mixt- 

 ures cotton oil has been used in greater proportions than indicated 

 above, thus corroborating the results obtained by the other methods of 

 analysis. Judged by the index of refraction alone, on the assumption 

 that this index for the stearines is not much different from that of lard, 



