112 



FOODS AND FOOD ADULTERANTS. 



Iii Table No. 13 will be found percentages of albumen remaining iu ni- 

 trate from lead acetate precipitation of forty-two samples taken from 

 those represented in Table No. 10. From these two tables it is at once 

 seen that the quantity of lawo-rotatory matter remaining in milk after 

 treatment with basic lead acetate is much greater than in those samples 

 treated with the two mercuric salts. This explains at once the higher 

 percent, of milk sugar obtained by using the last-named reagents, and 

 shows that the use of lead acetate as a clarifying agent must be aban- 

 doned : 



TABLE No. 13 Per cent, albumen after precipitation by lead acetate. 



COMPARISON OP RESULTS OBTAINED BY EXTRACTION WITH ALCOHOL AND POLARI/A- 



TION. 



By consulting Table No. 10, it will be seen that the percentage of sugar 

 obtained by extraction with alcohol is practically the same as that got 

 by polarization of the lead acetate nitrate. 



Thus, the mean percentage of sugar by alcohol (65 analyses) is 4.32 ; 

 by lead acetate, cold (53 analyses) is 4.34 ; by lead acetate, hot (64 anal- 

 yses) is 4.38; by mercuric nitrate, cold (61 analyses) is 4.58; by mer- 

 curic nitrate, hot (24 analyses) is 4.63. 



If now the milk sugar, as has already been intimated, exists in an 

 anhydrous state after extraction with alcohol, the percentage of it after 

 the addition of the molecule of water would be increased. Thus molec. 

 ular weight of anhydrous inilk sugar, 342: molecular weight of the 

 hydrous 360=4.38: x, whence the value of #=4.61. This agrees very 

 nearly with the number obtained by acid mercuric nitrate. 



By a study of Table No. 13 it is found that the mercuric iodide gives 

 nearly the same rotatory power as mercuric nitrate, and also by com- 

 bustion the nitrates from the milks clarified by lead acetate contain 

 more albumen than those prepared with mercuric iodide. There is, 

 therefore, every reason for believing that the numbers given by the 

 mercury salts are nearer the truth than those from the lead. 



It may be urged that the increased rotatory pow er observed by the 

 mercury salts is due to the conversion by the dilute acids of a part of 

 the lactose into galactose, which has a rotatory power greater than that 

 of milk sugar. But when it is remembered that the quantity of acid 

 introduced is extremely minute, tha.t ^he samples need not be warmed^ 



