CHAPTER IX 

 COMPOSITE SAMPLES 



Definition. In order to avoid testing each patron's milk or 

 cream every day for fat, a small sample, which represents the 

 average quality and a proportionate part of the whole, is taken 

 from each patron's milk every day and placed in a jar. A pre- 

 servative of some kind is previously placed in the jar to keep the 

 contents from spoiling. This is called a composite sample. 



When to Sample. Some makers prefer to sample the milk or 

 cream delivered every day; others prefer to sample every other 

 day. Some creamery operators, again, sample four or five times 

 in succession at intervals, the patrons being unaware of the time 

 when the sampling is to take place. The most reliable and prac- 

 tical method, however, is to take a sample every day, and test it 

 for fat at the end of every two weeks. When cream is received 

 composite samples do not give reliable results. In fact this 

 system has been very generally superseded by that of weighing 

 and testing the cream of each delivery or shipment. 



Kind of Preservatives to Add. While there are several pre- 

 servatives that may be used, such as salicylic acid, borax, boracic 

 acid, and bicarbonate of soda, those most commonly used are 

 bichromate of potash and corrosive sublimate (mercuric chloride) 

 either singly or as a mixture. Bichromate of potash, while 

 poisonous, is not extremely so and it imparts a color to the sample 

 which readily indicates its presence. It has, however, two 

 defects; if used in excess it is very much inclined to cause a 

 charred or burnt reading when the sample is tested, and if the 

 sample be exposed to light for any length of time a leathery scum 

 forms on the surface, which it is difficult to dissolve completely 

 by means of the sulphuric acid. 



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