TESTING MILK AND CREAM. 25 



After adding- the aeid to the milk in the test bot- 

 tle and mixing the two thoroughly, the test bottles 

 should be placed in the tester and whirled for five 

 minutes at whatever speed is indicated in the di- 

 rections given for the use of the machine. If 

 through any unavoidable delay, the test bottles get 

 too cool before the testing can be done, the bottles 

 should be heated to about 140° P. before placing 

 them in the tester. If the samples are tested when 

 too cold, the extraction of fat is not perfect, and the 

 fat column is neither so clear nor so well defined 

 as when the bottles have the proper temperature. 

 This heating can be done, either by placing the bot- 

 tles in hot water or in the tester, with the steam 

 turned on until they are sufficiently heated. Then 

 they may be whirled. The first five minutes whirling 

 can be done at a high temperature — as high as 200° 

 F. without interfering with the accuracy of the test ; 

 but the last three or four minutes whirling should 

 not be done at a high temperature — preferably 130° 

 F. When the testing is finished at too high a tem- 

 perature, the fat column contracts and sags a little 

 when the bottles are taken from the machine, and 

 this settling of the fat may cause a smeary and ill 

 defined meniscus, which interferes Avith the proper 

 reading of the fat column. If the reading is done 

 when the sample is too hot, the test will be too high. 

 At the end of the first five minutes whirling, add 

 hot soft water to fill the bottles up to the neck, and 

 whirl again for two minutes. After the second 

 whirling, add sufficient hot water to fill the bottle 

 to about the 8th per cent mark. Soft water should 



