354 SOPHISTICATION OF MILK PRESERVATIVES 



Another mefchod of calculating the probable percentage of added 

 witer is based on the assumed constancy of the sum of the " lacto- 

 meter degrees " (i.e., specific gravity x 1000 - 1000) and the percen- 

 tage of fat. This sum is generally about 36 and rarely falls below 

 34'5. Accepting this latter value as the minimum in genuine milk, 

 the percentage of added water is then given by the expression 



IQOfG+.F) 



34-5 

 where G = "lactometer degrees" and F = percentage of fat. 1 



Another way in which milk is impoverished is by the removal of a 

 portion of the fat, or, what comes to the same thing, the admixture of 

 skimmed or separated milk. The amount of fat removed can obviously 

 only be calculated if the amount originally present in the milk be 

 known. The usual plan is to assume that genuine milk contains 3 

 per cent fat, when the percentage of the total fat removed is given by 



100 - * 



It is evident, from the above figures, that the calculation of the 

 amount of added water or proportion of fat removed from a sample of 

 milk is based upon pure assumptions as to the real character of the 

 original milk. When the enormous variability shown by genuine milk 

 is taken into account, it will be seen how unreliable are the results of 

 such calculations. The most that can be said of the results so obtained 

 is that they probably express the lower limits of the alleged sophisti- 

 cation. 



Detection of the Presence of Preservatives. 



1. Boric acid or borax. This is easily detected in the ash of the 

 "milk (best obtained by igniting the residue left on evaporating the milk 

 with lime water) by the well-known cherry-red colour which is shown 

 by turmeric paper when dipped into a dilute hydrochloric acid solution 

 of the ash and dried at 100. As a confirmatory test the reddened 



paper should be moistened with very dilute caustic soda solution, 

 when a blue-black colour will be produced. 



2. Salicylic acid. About 50 c.c. of the milk are mixed with an 

 .acid solution of mercuric nitrate and the coagulated proteids and fat 



filtered off. The filtrate is then shaken with ether or (better) a mix- 

 ture of ether and petroleum spirit, in which the salicylic acid dissolves. 

 The ethereal solution is then evaporated and a drop of neutral ferric 

 ^chloride solution added to the residue ; a violet colouration then indicates 

 ^the presence of salicylic acid. 



3. Benzole acid. The milk is made alkaline with lime water and 

 ^evaporated with calcium sulphate or pumice to dryness on the water 

 toath. The residue is then powdered, moistened with dilute sulphuric 

 acid, and extracted with dilute alcohol. The alcoholic solution is 

 neutralised with lime water and evaporated to small volume ; the 

 residue is then slightly acidified with dilute sulphuric acid and extracted 

 with ether. The ethereal solution is then evaporated, when the 



1 Richmond, Dairy Chemistry. 



