A DAIRY LABORATORY GUIDE 1 9 



acid is next added, and if formaldehyde is present 

 a lavender-colored ring will appear between the 

 layer of acid and the layer of milk. If the contents 

 of the bottle are slowly mixed the dissolving casein 

 will take on a lavender color. The test will not 

 work if the milk is too old or if too much of the 

 formaldehyde has been added to the milk. 



Sometimes sulphuric acid contains ferric salts as 

 an impurity; and when such is the case, the acid 

 will give the test for formaldehyde without the use 

 of ferric chloride. It is best however, to always 

 add the ferric chloride to make sure there is a ferric 

 salt present. 



EXPLANATION. MIXING SAMPLES OF 



BUTTER BEFORE TESTING FOR FAT 



OR MOISTURE 



Before testing a sample of butter for either 

 moisture or fat the sample should be thoroughly 

 mixed. Fat and water do not readily mix, and 

 special precautions must be taken to make the 

 sample uniform throughout. The butter should be 

 heated and stirred until it is about the consistency 

 of thick cream. Do not heat the butter too much, 

 as the water and fat will entirely separate and it is 

 difficult to remix them again. The sample should 

 then be cooled and stirred thoroughly while 

 cooling, else the fat will cool rapidly on the 

 outside and force all of the water towards 

 the middle of the sample. The cooling process 

 should be kept up until the sample is quite firm. 

 The heating and cooling may be accomplished by 

 placing the butter in any convenient vessel, such 

 as a glass-stoppered sample jar. The jar may then 

 be held under a water faucet or set in a dish of 

 water. 



