TESTING DAIRY PRODUCTS BY THE BABCOCK TEST. 73 



The bottles must be whirled and heat applied as directed, or 

 the separation is liable to be incomplete. Sometimes a cloudy- 

 fat can be cleared by heat and longer whirling. 



Nearly all of the above precautions must be observed to obtain 

 correct results by the method as originally proposed. 



TESTING SKIMMED MILK, BUTTER MILK AND WHEY. 



Skimmed milk, butter milk and all similar products usually 

 contain small amounts of fat, much less than one per cent. They 

 can be tested with the ordinary milk bottle in precisely the same 

 manner as whole milk, with sufficient accuracy for all practical 

 purposes. If greater accuracy is desired, however, a special 

 test bottle which holds twice as much as the ordinary bottle can 

 be used. In such a bottle twice the usual amount of milk and 

 acid are taken and the column of fat, being double in length, 

 can be read with greater accuracy. Each division on the scale 

 of this bottle corresponds to o.i per cent. Another bottle 

 known as the Ohlsson or "B & W" test bottle has recently been 

 devised for testing very small percentages of fat. This bottle 

 has two necks, the larger of which is to admit the milk to the 

 bottle, and the smaller is a very fine tube in which the fat is 

 measured. As claimed by the inventor, one can easily read o.oi 

 per cent on the tube, if it were desirable to do so. Inasmuch, 

 however, as it is impossible to estimate to much less than o.i 

 per cent by the Babcock test it is hardly worth while to read so 

 fine as .01 per cent. 



By exercising very great care the writer has been able to 

 obtain results with this bottle that compare very well with the 

 gravimetric method down to .05 per cent. In order to do this 

 the following precautions must be observed: The bottle must 

 be perfectly clean, otherwise small particles of fat will adhere to 

 the walls and not be removed by the centrifugal force. Twenty 

 cubic centimeters of sulfuric acid, specific gravity 1.82, must be 

 used, and the milk warmed to about 70 F. before the acid is 

 added. The machine must run 5 minutes at about 1,000 revolu- 

 tions per minute, and the bottles be kept at a uniform tempera- 

 ture, either by steam or hot water, during the time. The read- 

 ing of the scale should be taken immediately after the whirling 



