96 MODERN METHODS OF TESTING MILK 



samples, several plugs being drawn and placed in the 

 sample jar. The jar containing the material is then 

 placed in water heated to 80 F. and agitated with a 

 rotary motion until the ice-cream is melted. The mel- 

 ted cream is then poured through a cream-sampling 

 sieve (Fig. 33, p. 86) into a cup or beaker, any 

 lumps being rubbed through with the fingers. The 

 sample is then thoroughly mixed by pouring several 

 times from one beaker to another and the weighing is 

 made at once as in the case of cream (p. 87). 



The method of testing described by White is essen- 

 tially as follows : A 6-gram sample is weighed into an 

 ordinary milk-testing bottle. With a 6-gram sample, 

 one adds 4 cc. of sulphuric acid (sp. gr. 1.83) and 

 carefully mixes the cream and acid; after about two 

 minutes, one adds 4 cc. more of acid and again care- 

 fully mixes. The mixture should be of a light-brown 

 color; if it should be black, the test should be begun 

 again, another sample being weighed and less acid 

 used. The bottle is at once placed in the steam cen- 

 trifuge and whirled as rapidly as possible for three 

 minutes. The test is then completed by addition of hot 

 water and repeated whirling. It is best to add the hot 

 water in two portions, whirling three minutes after 

 the first .addition of water and two minutes after the 

 second addition. The percentage of fat shown is mul- 

 tiplied by three. 



In Holm's method, a mixture of equal parts of hy- 

 drochloric and 80 per cent, acetic acid is substituted for 

 sulphuric acid. A sample of 9 grams is weighed into a 

 milk-testing bottle, and 30 cc. of the acid mixture 

 added. The bottle is then placed in hot water and 



