MILK 



109 



chloride must have a sp. gr. of exactly l'1375,and when diluted 

 to 1 : 10 should show a refraction of 26 at 17*5 C. 



The contents of the tube is then well shaken, the reflux 

 condenser, which should be 22 cm. long, is attached, and the 

 tube placed in boiling water in a water-bath. For use where a 

 series of analyses have to be made, Ackermann has devised an 

 apparatus in which twelve to twenty-four glass tubes can be 

 heated (Fig. 51). 1 



In order to obtain a proper serum preparation, the boiling of 

 the water when the tubes are placed in it should be interrupted 

 for as short a time as possible. This is best achieved by the use 

 of a large Fletcher burner. 

 Boiling for fifteen minutes 

 is sufficient, and the tubes 

 are then Avithdrawn and 

 placed in a vessel containing 

 cold water ; after some little 

 time the temperature of the 

 water is raised to 17'5 C. 

 The small amount of water 

 which condenses in the 

 upper end of the tube in 

 which the coagulation is 

 taking place, and in the 

 condenser, is mixed with 



the serum without shaking. The serum can now be poured 

 off into a small beaker and used for the refractometer deter- 

 mination ; filtration is not necessary. 



Ackermann found as a mean of 2,800 investigations with this 

 method that the variations in the refractive index of normal 

 milk lay between 38'5 and 40'5 with the Zeiss immersion 

 refractometer. 



The influence of water in milk is shown in the following 

 table by Ackermann : 



FKI. 51. Water-bath for Ackermann' s 

 Method. 



1 To be obtained from Franz Hugershoff, Leipsic. 



