SAMPLING MILK AND CREAM 



127 



Pig-. 16. Composite 



sample jar 



Courtesy Mojon- 



nier Bros. Co. 



Pint jars sealed with glass stoppers, rubber 

 stoppers, cork stoppers, metal caps, or screw 

 tops may be used for this purpose. Bottles 

 with paper caps and jelly glasses with tin lids 

 do not furnish tight seals ; they should not be 

 used for this purpose. 



A separate jar is used for each patron, and 

 each jar must bear the respective patron's 

 number. The jars should be thoroughly clean 

 and, in order to guard against errors, they 

 should be arranged on convenient shelves near 

 the weigh can in numerical order, grouping the 

 jars of patrons of the same route together. 

 Taking Composite Samples of Milk. Cor- 

 rect composite samples may be obtained by 

 the use of a milk thief or a graduated pipette. 

 If the milk thief is used, it is inserted into the 

 weigh can of the entire delivery of one patron. 

 The milk in the tube rises to the level of the 

 milk in the weigh can. The milk thief is then emptied into the 

 sample jar. In case the graduated pipette is used, a certain 

 quantity of milk is taken for every pound of milk delivered by 

 the patron (usually about .1 c.c. for every pound of milk de- 

 livered). The milk thief is the handier instrument of the two, 

 but where the amount of milk delivered by different patrons 

 varies considerably, the samples of milk from the larger milk 

 producers are often too large to be practical. 



Other so-called composite samples are taken by using the 

 same measure for all milk receipts. In this case a small dipper 

 holding about one ounce is generally used. With this dipper 

 a sample of milk is taken daily from the weigh can of each 

 patron's milk and transferred into the sample jar. This method 

 of composite sampling is not mathematically correct and the 

 results tend to be less reliable, although experimental data by 

 Hunziker show that the results average practically the same as 

 when aliquot portions are taken. 



The chief objection to composite samples of milk is that 

 they are usually held too long before testing. This causes more 

 or less complete separation of the butterfat, in the form of a 



