166 Testing Milk and Its Products. 



through which the milk passed from the weighing can; 

 the other was taken from the weighing can by means 

 of a Scovell sampling tube. The following percentages 

 of fat were found in each of these samples r 1 



PRESERVATIVES FOR COMPOSITE SAMPLES. 



189. When milk is kept for any length of time under 

 ordinary conditions, it will soon turn sour and become 

 loppered, and further decomposition shortly sets in, 

 which renders the sampling of the milk both difficult 

 and unsatisfactory (19). The period during which milk 

 will remain in an apparently sweet or fresh condition 

 varies with the temperature at which it is kept, and 

 with the cleanliness of the milk. It will not generally 

 remain sweet longer than two days at the outside, at 

 ordinary summer or room temperature. 



In order to preserve composite samples of milk in a 

 proper condition for testing, some chemical which will 

 check or prevent the fermentation of the milk must be 

 added to it. A number of substances have been pro- 

 posed for this purpose. 



190. Bi-chromate of potash. This preservative is 

 preferred by many because it is relatively harmless, 

 cheap and efficient. The bi-chromate method for pre- 

 serving samples of milk was proposed by Mr. J. A. 

 Alen, city chemist of Gothenburg, Sweden, in 1892, 2 



1 See also 199 et seq. 



2 Biedermann's Oentralblatt, 1892, p. 549. 



