164 MILK 



If the temperature is too low the bottles should be placed 'in a 

 water-bath of 140 F. for some minutes before reading is taken. 

 Sammis states that reading between 110 and 150 F. gives prac- 

 tically the same results, the difference owing to expansion with 

 increasing temperature being negligable. In cream testing the 

 temperature must be controlled more accurately. 



The mixture of milk and acid need not be centrifuged immedi- 

 ately after mixing, but will give accurate results if kept for some 

 time. However, when not centrifuged immediately after mixing 

 the fluid must be warmed in a water-bath at 71 C. (160 F.). 



The test bottles must be washed after each test is finished 

 before the fat solidifies. The contents, while still warm, may be 

 emptied into a waste jar (Fig. 57). A solution 

 of potassium bichromate 60 parts, in water 

 300 parts and concentrated sulphuric acid 460 

 parts or a strong alkali or soda solution can be 

 used after the bottles have been rinsed in hot 

 water. A little ether will facilitate the solu- 

 tion of lumps of fat adhering to the glass. 

 A tube brush is often necessary to clean out 

 the neck. Special bottle holders have been de- 

 Fig. 57. Waste vised by means of which a number of bottles 

 jar for Babcock test can b e washed at the same time, and by in- 

 202 U Agri. ( E^ Sto! verting the holder the water can be drained out 

 of Colo. Agri. Coll.) of the bottles. A bottle holder suitable for 



this work is illustrated in Fig. 58. 



There are some devices which facilitate the work when a large 

 number of tests are made. The acid can be run into the test bottles 

 from a large container which has a buret attached (Fig. 59). An- 

 other style has a side tube attached which is just large enough to 

 hold the requisite amount of acid when filled (Fig. 60), Finally, 

 a dipper has been constructed which holds 17.5 c.c. of sulphuric 

 acid (Fig. 61). Other devices aim to facilitate the adding of hot 

 water. One style of centrifuge has a water container attached, 

 from which hot water can be distributed to the bottles by means 

 of a rubber hose. Or a special vessel containing hot water is kept 

 near the centrifuge and the water distributed by means of a rubber 

 hose. Automatic pipets have also been devised. 



When a large number of samples are tested at the same time 

 it is well to first place the milk in the bottles, arranged in a suit- 

 able rack (Fig. 62), then proceed to add the acid. Otherwise 

 the first bottles will cool before centrifugation is possible. To avoid 

 this it is advisable to place the bottles in a water-bath at 160 F. 

 and keep them there until all bottles are ready for the centrifuge. 

 Modifications of the Babcock Test. The Russian Test. 



