i MILK 101 



The mean composition of cow's milk, and the variations in 

 different districts are, however, so uncertain, depending as they 

 do upon the breed, climatic and other conditions, that the most 

 satisfactory way, without doubt, is to determine the average 

 composition of the milk of a district and the fluctuations to 

 which it is subject. To do this, a very large number of milk 

 analyses, made by competent persons, would have to be collected 

 in that particular district. 



I. THE ADDITION OF WATER. 

 1. The Nitrate Test. 



Fuchs * was probably the first to recommend the detection of 

 added water in milk by testing it qualitatively for nitric acid. 

 He assumed, which is hardly correct, that the water from most 

 wells and supplies contains small quantities of nitric acid. As 

 a test for nitric acid or nitrates, UrYelmann 2 used the well- 

 known reaction with diphenylamine and sulphuric acid, which 

 give a blue coloration in the presence of N 2 O 5 . Schrodt 3 

 showed that pure milk does not contain the slightest trace of 

 nitric acid or nitrates even after the food has been mixed with 

 considerable quantities of saltpetre. Two methods of employing 

 the " nitrate test " are as follows : 



(a) SoxMet's* Nitrate Test. 



One hundred c.c. of milk are boiled after the addition of 

 1*5 c.c. of a 20 per cent, solution of calcium chloride, then to a 

 small portion of the filtrate as many drops of a 2 per cent> 

 solution of diphenylamine in concentrated sulphuric acid are 

 added as will impart a milkiness. Two c.c. of the liquid which 

 has been prepared in the above way are then poured into about 

 an equal quantity of concentrated sulphuric acid contained in a 

 test-tube in such a way as to keep the liquids separate. In the 

 presence of nitrites or nitrates, a blue ring forms at the junc- 

 tion of the two liquids. Where the quantity of nitrates is about 



1 Vierteljahrwchrift, fiir iiffentliche Gesundheitspfle.ye, 1880, p. 253. 



2 Zeitschrift fiir analytische Chemie, Vol. XXIII, p. 429. 



3 Jahresbericht der Milchimrtschaftlichen Versuchsstation Kiel, 18841885 ; 

 see also Henseval and Mullie, Revue Gen. du Lait, Vol. IV, p. 512 ; and 

 Marcas and Huyge, Ibid. , Vol. V, p. 385. 



4 Herz, Die Kuhmilch, p. 49. 



