Composite Samples of Milk. 155 



obtained by the use of the drip sampling method and the 

 Scovell tube. Two composite samples were taken from 

 fifty different lots of milk, amounting to about 6,000 Ibs. 

 in the aggregate. One sample was taken of the drip 

 from a hole in the conductor spout 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: 1 



Gravimetric 

 Babcock test. analysis. . 



Drip composite sample 4.0 per cent. 4.04 per cent. 



Scovell tube composite sample.. 4.0 per cent. 4.06*per cent. 



PRESERVATIVES FOR COMPOSITE SAMPLES. 



187. When milk is kept any length of time under ordi- 

 nary conditions, it will soon turn sour and become lop- 

 pered, and further decomposition shortly sets in, which 

 renders the sampling of the milk both difficult and un- 

 satisfactory (19). The changes which occur when milk 

 sours are due to the formation of lactic acid by the action 

 of bacteria on milk sugar; the acid coagulates the casein 

 of the milk, but does not destroy or attack the butter 

 fat (32). 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 



i See also 189 et seq. 



