216 THE DETECTION OF ADDED SUBSTANCES. 



addition of alkali. The alkalinity of the ash should be estimated 



N 

 by titrating with acid, using phenol- phthalein as indicator ; 



1 c.c. of the acid is with this indicator equal to 0-0106 gramme 

 of Na 2 C0 3 . 



Other mineral additions, such as boric acid, borax, fluorides, 

 etc., may be added as preservatives, and not to mask the addition 

 of water ; the methods of detecting these have been given. 



It has been alleged that salts of ammonia have been added 

 to raise the total nitrogen. These would be detected by rendering 

 alkaline with magnesium carbonate, distilling the milk, and 

 testing the distillate with Nessler's reagent (an alkaline solution 

 of mercuric chloride in potassium iodide). 



Detection of Sterilised Milk in New Milk. To distinguish 

 new milk on the one hand from milk which has been sterilised 

 on the other, the following methods may be employed : 



(1) Place 100 c.c. of milk in a graduated cylinder (or fill a 

 " creamometer ") and allow it to stand for six hours at a tem- 

 perature of 60 F. (15-5 C.) ; note the percentage of cream. If 

 less than 2-5 per cent, of cream for each 1 per cent, of fat in the 

 milk has risen to the surface, the milk may be considered suspi- 

 cious. If the quantity of cream falls markedly below 2 per cent, 

 for each 1 per cent, of fat, it is highly probable that sterilised 

 milk is present. 



Revis has pointed out that the amount of cream for each 1 per 

 cent, of fat varies greatly according to the temperature of setting, 

 and mechanical treatment of the milk before setting, and con- 

 sequently that this test is only of very approximate value. 



(2) Estimate the albumin by the method of Hoppe-Seyler 

 or, better, that of Sebelein. If less than 0-35 per cent, is found, 

 sterilised milk may be considered to be present. 



(3) Estimate the milk-sugar by the polariscope, and also 

 gravimetrically in duplicate ; if the difference between the two 

 estimations be more than 0-2 per cent., it will be corroborative 

 evidence of the presence of sterilised milk. 



(4) To about 5 c.c. of milk add as much powdered para- 

 phenylene-diamine as will lie on the point of a knife, and shake 

 well ; on the addition of a drop or two of a 10-volume solution 

 of hydrogen peroxide fresh milk gives a blue coloration ; " pas- 

 teurised " milk gives a similar reaction, not, however, so marked ; 

 while " sterilised " milk gives no coloration within ten minutes. 

 A mixture of " sterilised " and fresh milk will give the characters 

 of " pasteurised " milk. 



The hydrochloride of meta-phenylene-diamine may be sub- 

 stituted with advantage for the para-compound. The coloration 

 is paler, and not quite so quickly developed. By shaking with 



