26 MILK AND DAIRY PRODUCTS PART 



here. When buying a lactometer its accuracy should first of 

 all be tested against a pyknometer or a Westphal balance. 



As has been mentioned (p. 22), the specific gravity of sour, 

 coagulated milk can be determined by means of Weibull's 

 method. The formula which Weibull uses for the mixture 

 of milk and ammonia is : 



_ (M + A.}S' - A.S" 



M 

 Where 



S = sp. gr. of the milk. 



S' = milk-ammonia liquid. 



S" = ammonia. 



M = the volume of milk in c.c. 



A = ammonia in c.c. 



The most important application of the specific gravity of 

 milk is when testing for the addition of water or the removal 

 of cream. A return, therefore, will be made to this subject 

 in the section dealing with milk adulteration 



II. Estimation of the Dirt. 



The estimation of the amount of dirt, that is, the solid 

 impurities, in milk, is of importance hygienically. F. Renk 

 was the first to show the value of a quantitative determination 

 of the dirt in milk. 1 A fairly satisfactory method for carrying 

 out Renk's principle has been proposed by A. Stutzer. 2 



Stutzer's apparatus consists of a bottle of the usual shape, 

 capable of holding 1 litre. An ordinary test-tube, without the 

 usual turned-back edge, is connected to the neck of the bottle 

 by means of a piece of rubber tubing. Before fitting the 

 rubber tubing, to one end of which the test-tube is attached, 

 on to the neck of the bottle, the latter is filled with 1 litre of 

 the milk which is to be examined. Then the free end of the 

 rubber tubing is fitted on to the bottle, and the latter inverted 

 and held in this position by means of a retort stand and ring, 

 the test-tube now occupying the lower position. After 1 or 



1 Verhandl. des X internat. med. Kongr., Berlin, 1891, Vol. V, p. 164 ; also 

 Milch- Zetiuwj, 1893, p. 594, and 1899, p. 65 ; further, Molkerei-Zeitung, Berlin, 

 1898, p. 405. 



2 Die Milch als Kiudernahruny, cfcc., Bonn, 1895, p. 5. 



