PER CENT OF FAT IN BUTTER 113 



" III. Centrifuging. Insert the separatory funnel in the 

 special socket, allowing the stem to project through the hole in 

 the bottom and the handle of the stopcock through the open side. 

 CAUTION. The socket must always be placed in the centrifuge, 

 with the open side facing the direction in which the wheel revolves. 

 This is very important, if the opening faces the reverse direction 

 the stopcock will be thrown out and broken. Whirl one minute 

 at the same speed used in testing milk with the Babcock test. 

 The centrifuge must be kept warm. 



* IV. Removing the Water. Remove the separatory funnel 

 from the socket and allow the water to flow through the stopcock 

 until the fat (or curd) is within one-eighth of an inch of the stop- 

 cock. In this and later operations involving the stopcock one 

 must be sure it does not stick. It must always be under control, 

 and it is best to give it frequent slight movements when the water 

 or acid is running through it to be sure that this control is main- 

 tained; otherwise it might stick at a critical moment and the 

 determination be lost. The most of the salt and part of the curd 

 are taken out by the water. The remainder of the curd and all 

 of the fat stays in the funnel. If it is desired to determine the 

 salt, this wash water is allowed to run into a 250 c.c. flask and the 

 operation described in this paragraph conducted three times 

 instead of but once, the wash water being added each time to 

 the flask. 



" It sometimes happens that the water will not start flowing 

 when the stopcock is opened, in which case it can be started by 

 blowing into the mouth of the separatory funnel. 



4 V. Dissolving the Curd. Measure out 9 c.c. of cold water, 

 preferably condensed steam, with the glass graduate and pour 

 into the beaker. Add to this 1 1 c.c. of sulphuric acid of the same 

 strength used in testing milk and cream (specific gravity, 1.82- 

 1.83) and mix by gently shaking. (CAUTION. Always add acid 

 to water and not water to acid, or a serious accident may result.) 

 While still very hot add the mixture to the contents of the separa- 

 tory funnel. Now dissolve the curd by giving the funnel a 

 circular motion with the hand grasping the neck. Centrifuge 

 one minute, as before. Draw off the acid solution till the fat 



