270 Chemical Tests and Analyses 



bottles containing the mixture of milk and acid are then whirled in 

 the Babcock tester for five minutes at about one thousand revolu- 

 tions per minute, in the case of a tester with a twelve-inch diameter 

 wheel. Fill the test bottles to the bottom of the neck with hot 

 water. The water should be soft, preferably rain water or distilled 

 water. If hard tap water is used it should be boiled to precipitate 

 the carbonates, otherwise the test may be difficult to read, owing to 

 the presence of bubbles of gas on top of the fat column. Revolve 

 again at full speed for two minutes, fill the test bottles to near the 

 top of the graduation with hot water. Whirl in the centrifuge for 

 one minute. Now set the test bottles in the wlater bath at 135 

 degrees F. for five minutes. - The test is now ready to be read. 

 The figures on the test bottles represent per cent. In the case of 

 the 8 per cent standard milk test bottle the sub-divisions represent 

 tenths per cent. Read from the bottom of the lower curve to the 

 top of upper curve of the fat column, including the meniscus in the 

 reading. 



GRAVIMETRIC METHOD— PAPER COIL 



"Make coils of thick filter paper, cut into strips 6.25 by 62.5 

 cm., and thoroughly extract with ether and alcohol, or correct the 

 weight of the extract by a constant obtained for the paper. From 

 a weighing bottle or weighing pipette, transfer about 5 grams of 

 milk to the coil, care being taken to keep the end of. the coil held 

 in the fingers, dry. Dry the coil, dry end down, on a piece of glass 

 at the temperature of boiling water; transfer to an extraction ap- 

 paratus and extract with absolute ether or petroleum ether boiling 

 at about 45 degrees C. ; dry the extracted fat and weigh." 



ROESE-GOTTLIEB METHOD 



"Weigh 10-11 grams of the milk into a Rohrig tube or some sim- 

 ilar apparatus, add 1.25 c.c. of concentrated ammonium hydroxid 

 (2 c.c. if the sample is sour) and mix thoroughly. Add 10 c.c. of 

 95 per cent alcohol by volume and mix well. Then add 25 c.c. of 

 washed ether and shake vigorously for thirty seconds, then 25 c.c. 

 of petroleum ether (redistilled slow^ly at a temperature below 60 de- 

 grees C.) and shake again for thirty seconds. Let stand twenty 

 minutes, or until the upper liquid is practically clear. Draw off as 

 much as possible of the ether-fat solution (usually 0.5-0.8 c.c. will 



