616 TESTING FOR BUTTERFAT 



from such a sample. Avoid incorporation of air bubbles while 

 mixing the sample. 



Curdy and churned samples are not dependable. Sour and curdy 

 samples should be treated as follows: add one-half teaspoonful of 

 soda lye or potash lye, shake, and let stand until all lumps of curd 

 have disappeared. The sample is then ready for the test. When 

 testing samples to which soda lye or other alkali has been added, the 

 acid should be added slowly and carefully to avoid accidents and to 

 prevent the loss of a portion of the contents of the bottle by exces- 

 sive effervescence. 



Measuring the Milk Into the Test Bottle. Use standard milk 

 test bottles and a standard 17.6 cubic centimeter pipette. Measure 

 17.6 cubic centimeters (representing 18 grams) of the properly 

 prepared sample into the test bottle. In order to do this rapidly, 

 and without spilling, the delivery tube of the standard pipette 

 has been constructed of such diameter, that this tube readily 

 drops into the neck of the standard "8 per cent milk test 

 bottle. Hence drop the delivery tube of the pipette into the 

 neck of the test bottle until the bulb of the pipette rests on the 

 neck of the bottle, then release the milk. Blow the last drop of 

 milk out of the pipette before removing it from the bottle. Mark 

 each bottle with a number corresponding with the number of the 

 respective patron on the sample bottle. The marking is best done 

 with an ordinary lead pencil on the etched shoulder of the test bot- 

 tle^ Or equip the test bottles with metal tags which bear consecu- 

 tive numbers. Slip one tag over the neck of each test bottle. In 

 this case the test bottle number may and usually does differ from 

 the patron's number shown on the sample bottle. It is necessary 

 therefore, to record the test bottle number on the test report blank 

 opposite the respective patron's name or number at the time of rill- 

 ing each test bottle. 



Adding the Acid. Use commercial sulphuric acid, specific 

 gravity 1.82 to 1.83. The temperature of the acid should be the 

 same as that of the milk, 55 degrees F. to 70 degrees F. In order 

 to insure the proper temperature of the acid it is advisable to set 

 the acid bottle into the tank containing the milk sample bottles. 



Add 17.5 cc. of acid to the milk in the test bottle and mix by 

 giving the bottle a rotary motion until the lumps of curd are com- 

 pletely dissolved and the mixture presents a brown-black color. It 



