Composite Samples of Milk. 169 



194. Care of composite samples. The composite 

 sample jars should be kept covered to prevent loss by 

 evaporation, and in a cool, dark place, or at least out 

 of direct sunlight when bi-chromate of potash is used 

 as a preservative; the chromic acid formed by the re- 

 ducing influence of light on chromate solutions pro- 

 duces a leathery cream which is difficult to dissolve in 

 sulfuric acid. 



A coating of white shellac has been suggested to pro- 

 tect the labels of the composite sample jars. The shel- 

 lac is applied after the names of the patrons have been 

 written on the labels, and when these have been put on 

 the jars. Gummed labels, 1x2% inches, answer this 

 purpose well. 



Numbers are sometimes ground on the sample jar or 

 stamped on brass tags attached to the jars by a wire. 



In keeping the milk from day to day, care should be 

 taken that the cream forming on the milk does not stick 

 to the sides of the jars in patches above the level of the 

 milk. Unless the daily handling of the jars and the 

 addition of fresh portions of milk be done with suffi- 

 cient care, the cream will become lumpy and will dry 

 on the sides of the jars. In some cases it is nearly im- 

 possible to evenly distribute this dried cream through 

 the entire sample at testing time so as to make the com- 

 posite sample a true representative of the different lots 

 of milk from which it has been taken. 



195. Every time a new portion of milk is added to 

 the jar this should be given a gentle horizontal rotary 



