10 DEPARTMENT OF AGRICULTURE. 



allow the air to pass out of the bottle. Blow lightly through the pipette to ensure 

 that the last drops of milk run into the bottle. It is very important that no milk 

 is lost during the process by mixing, measuring, and transferring to the test-bottle, 

 as the Babcock test is essentially quantitative and the slightest loss affects its 

 accuracy. 



ADDING THE ACID. 



The next step is adding the acid. For this purpose commercial sulphuric acid 

 is commonly used. This can be purchased from any reliable dairy-supply house. It 

 must be handled very carefully, as it is extremely corrosive. If acid gets on the 

 hands or clothes it should be immediately washed off with cold water. The acid 

 absorbs water very readily, and for this reason should be kept in a tightly stoppered 

 bottle. 



The exact amount of acid to use will depend largely upon the strength of the 

 acid and the temperature of the milk to be tested, but under ordinary conditions 

 17.5 c.c. will be found approximately correct. 



The temperature of both the acid and the milk should be about 60 to 70 Fahr. 

 If too warm, the acid will act too vigorously and some of the milk solids will be 

 charred, causing a black substance to rise with the fat and obscure the test. On 

 the other hand, if too cold, all the solids will not be fully dissolved, and a clouded 

 fat column will result. With a little individual experimenting the operator can 

 soon discover the proper amount to use. 



To prevent the charring or the burning of any part of the milk, the acid should 

 be poured slowly down the side of the bottle until all has been added, slowly revolv- 

 ing the test-bottle during the process in order to wash down the milk which clings 

 to the neck of the bottle. The acid and milk should be mixed by thorough shaking 

 with a gentle rotary motion, so that the acid will act uniformly on all parts of the 

 milk. Mixing should be continued until all the curd is dissolved and the liquid has 

 turned to a dark, coffee-coloured brown, which soon changes to black. At this stage 

 considerable heat has been produced. This high temperature keeps the fat in a 

 finely suspended liquid state, so that it can be readily separated from the remainder 

 of the liquid. 



WHIRLING THE BOTTLES. 



It is important that the bottles be placed in the machine before they become 

 cool, otherwise they should be placed in warm water to maintain an even tempera- 

 ture. The bottles should be placed in the machine opposite each other, so as to 

 evenly balance the machine. The samples should be whirled at full speed, according 

 to the directions on the body or on the crank of the machine, for five minutes. The 

 object of this whirling is to separate the fat from the remainder of the liquid, so 

 that it can be gathered into the neck of the bottle and measured. It is important 

 to keep the bottles hot during the entire process, and for this reason the machine 

 should be operated in a warm place during the colder seasons and with hot water in 

 the machine. 



After the five minutes' whirling the machine is stopped for the purpose of 

 adding hot water to each bottle for the purpose of floating the fat up to the neck 

 of the bottle. Soft water is preferable, and it should have a temperature of not 

 less than 140 Fahr. Enough water is added to bring the fat up to the neck of the 

 bottle. A pipette, or small pitcher, or a cup with a V-shaped spout can be used 

 to add the water. 



Whirl again for two minutes at full speed. Then add sufficient hot water to 

 bring the fat above the zero, but not above the 8- or 10-per-cent. mark. Whirl one 

 minute more to finish the operation. The bottles should now be removed from the 

 tester and placed in a hot-water bath, having a temperature of 130 to 140 Fahr., 

 to avoid too rapid cooling of the fat. This should be done in all but the warmest 

 weather. Butter-fat expands and contracts rapidly with changes of temperature, 



