MILK TESTS 447 



In detail the test is made as follows : The milk to be sampled is 

 thoroughly mixed by pouring it several times from one vessel to another. 

 By means of a milk pipette, or measure, graduated to hold 17.6 cc, 

 this quantity of milk is transferred to a special form of bottle, which 

 has a capacity of a little more than one ounce and a long neck with 

 graduations or per cent marks from to 10. The cubic capacity of 

 the neck, from to 10, is exactly 2 cc. This is the volume of 1.8 grams 

 of melted fat, which is the substance to be measured on the scale. As 

 the bottle is so graduated that 1.8 grams represents 10 per cent, it 

 is necessary to use a sample weighing ten times as much, or 18 grams, 

 and it is found that the 17.6 cc. pipette will deliver approximately 

 this weight of milk. There is then added 17.5 cc. of concentrated 

 commercial sulfuric acid, having a specific gravity of 1.82 to 1.83. 

 The acid and milk are mixed by a rotary motion. The action of 

 the acid on the water and solids of the milk generates considerable 

 heat. The sample is promptly placed in a centrifugal machine and 

 whirled for five minutes. Hot water is then added to bring the fat 

 to the base of the neck. It is then whirled two minutes, and more 

 hot water is carefully added until the fat rises in the neck so that it is 

 opposite the graduations. The sample is then whirled one minute, 

 to insure collecting as much fat as possible in the neck. While the fat 

 is still warm, its percentage is ascertained by reading the marks at its 

 upper and lower levels and taking the difference between them. 



The cost of a small complete outfit for testing milk is $6 to SIO. 



Computing total sol'ds of milk. 



Babcock and Richmond have proposed formulae for computing the 

 total solids of milk. One of the best is : — 



- + 1.2 F + .14 = total solids. 

 4 



L represents the second and third decimal figures of the specific gravity, 

 or the Quevenne reading, and F represents the percentage of fat. This 

 formula is used largely, and for practical purposes agrees closely enough 

 with results of gravimetric analysis. 



Test for acid in milk (Pearson). 



It is not practicable to isolate lactic acid from milk and measure it as 

 milk-fat is measured. But its quantity can be easily determined by 



