METHODS OF EXAMINING MILK 235 



obtain accurate results, every particle of milk must be 



delivered into the bottle. The measuring cylinder is 



filled to the 17.5 c.c. mark with sulphuric acid; then, 



with the bottle held by the neck in an oblique position, 



the acid is poured slowly down the side, the bottle being 



rotated slowly so that any milk in the neck will be washed 



down. The acid and milk are then mixed by grasping 



the bottle by the neck and gently whirling it, first to the 



right and then to the left, or by holding the bottle by 



the neck in an inclined position with the edge of the bot- 



tom resting on a table and rotating it, 



first in one direction and then in the 



other. When mixing is once com- 



menced it must be continued until 



solution is complete. The solution 



should finally be of a dark brown color, 



The bottle is placed in a centrifuge 



and whirled for five minutes at a speed 



of 800 to 1200 revolutions per minute. ^ ^ 



Fio. 35. Cylinder used 



Hot water at a temperature above 



175 



CO 



120 R (49 C.) is then added until 

 the bottle is filled to the bottom of the u - s ' Dept ' f AgricuUure0 

 neck and the bottle is replaced in the centrifuge and 

 whirled for two minutes. Hot water is again added until 

 the fluid in the bottle is raised to a point near the top 

 of the graduated scale, the water being dropped directly 

 into the fluid, not run down the side, in order to remove 

 any flocculent material which may be entangled in the 

 fat at the top. The bottle is then whirled another min- 

 ute. After the whirling is completed, the fat should be 

 collected at the top of the fluid in the bottle in a column 

 of clear, yellowish liquid, with a nearly colorless fluid 

 below it. The fat column should have a well-defined 



