204 CHEMISTRY OF FARM PRACTICE 



solution to 50 cubic centimeters of the concentrated acid 

 (sp. gr. 1.20). Place 10 cubic centimeters of the milk in 

 a casserole or a porcelain evaporating dish, add an equal 

 volume of the prepared acid and heat the mixture nearly 

 to boiling. While heating, swirl the contents of the dish 

 gently so as to break up the curd. 



The presence of formaldehyde is indicated by a violet 

 color varying in intensity with the amount of formaldehyde 

 present. If no formaldehyde is present, the mixture turns 

 brown. 



151. Detection of Boracic Acid. To 10 cubic centimeters 

 of the milk add 6 drops of concentrated hydrochloric acid 

 and mix thoroughly. Dip a strip of turmeric paper in the 

 mixture and dry the paper by wrapping it about a test-tube 

 which contains boiling water. In the presence of boracic 

 acid or a borate the turmeric paper, which is a reddish-brown 

 color, will turn to a greenish-black color upon treatment 

 with a drop of sodium hydroxide. 



152. Testing Milk for Per Cent of Fat. The Babcock 

 test is a rapid, accurate, and inexpensive method for deter- 

 mining the amount of fat in milk and other dairy products. 



For making the test, a centrifuge, two forms of which are 

 shown in Fig. 67 and the test bottles, pipette for measuring 

 the milk, acid measure, brush for cleaning the bottles, and 

 sulphuric acid, shown in Fig. 68, are required. 



The neck of the test bottles are marked with a graduated 

 scale, each small division representing two-tenths of 1 

 per cent of fat. Every fifth division is a long one and repre- 

 sents 1 per cent. In making the test 17.5 cubic centimeters 

 of milk, which weigh 18 grams, are first slowly run into the 

 bottle by means of the pipette, holding the pipette at an 

 angle as is shown in Fig. 69. This method of running in the 

 milk prevents overflowing due to the stopping of the outlet 

 for air. 



The reason for the use of 18 grams of milk is that the neck 

 of the test bottle is graduated to hold just 2 cubic centi- 



