18 THE STORY OF MILK 



It may not always be convenient to make a test im- 

 mediately when the sample is taken. In the creamery 

 where the milk is paid for according to its fat con- 

 tents, samples are taken every day from every patron's 

 milk and it would take too much time for the butter 

 maker to test all of these samples before they would 

 spoil. A preservative, corrosive sublimate, — poisonous 

 but all right for the purpose, — is therefore added and 

 all the samples of one farmer's milk for several days 

 or a whole week are put together in one glass to be kept 

 and tested at one time. This is called a composite test 

 and has proven entirely satisfactory. 



The Lactometer has been used to discover adultera- 

 tions, depending upon the difference in specific gravity 

 of the various constituents. The specific gravity of 

 whole milk is about 1.032 which means that, if a certain 

 volume of water weighs 1.000 weight units, the same 

 volume of whole milk weighs 1.032, the same volume 

 of butter-fat weighs, say, .900, or of cream about 1.000, 

 and of skim milk 1.036 units. If the Lactometer shows 

 a sample of milk to have a higher specific gravity than 

 1.032 it may therefore be suspected of having been 

 skimmed. But it will readily be seen that by removing 

 from whole milk some of the cream and adding water, 

 the specific gravity can easily be brought back to normal 

 for whole milk. This test is therefore unreliable and has 

 been discarded with the advent of the Babcock. 



fat in the milk. The bottle with contents should be warm — about 140° — • 

 when the measure is taken. 



For testing skim milk and cream special forms of test bottles are 

 used — which are described in the circulars coming with the testers and 

 students who desire fuller information are referred to Farrington and 

 Woll's "Testing Milk and its Products," published by the Mendota 

 Book Co., Madison, Wis. 



