25 



TESTING BUTTERMILK AND WHEY FOR FAT. 



Buttermilk and whey are tested in exactly the same 

 manner as skim milk, except that whey, having less solids 

 not fat, requires but about half the quantity of acid. 



PRESERVING SAMPLES. 



If for any reason it is desired to keep a sample of milk 

 or cream for a few days before testing it, a preservative 

 should be added to prevent decomposition. Formalin 

 (which is a 40 per cent solution of formaldehyde) , corrosive 

 sublimate (mercuric chlorid), or potassium bichromate 

 are used for this purpose. Formalin has the advantage of 

 being a liquid and easily handled; on the other hand, it 

 has the property of toughening the casein and rendering it 

 more difficult to dissolve later in the sulphuric acid. One 

 cubic centimeter should keep a pint or quart of milk or 

 cream for two weeks or more. Corrosive sublimate, while 

 the most powerful of the three, is a deadly poison. Sam- 

 ples preserved with it should be colored in some way to 

 indicate the presence of the poison. Tablets of corrosive 

 sublimate containing coloring matter are on the market. 

 If potassium bichromate is used, the samples should be 

 kept in a dark place; 15 to 20 grains is sufficient to pre- 

 serve a pint for a reasonable length of time. 



CLEANING THE TEST BOTTLES. 



After the test, and before the test bottles have become 

 cold, they should be emptied with a shake or two to loosen 

 the grayish-white deposit of calcium sulphate which accu- 

 mulates on the bottom. A convenient device is shown 

 in figure 22. This consists of a 5-gallon stone jar with a 

 wooden cover in which one-half-inch holes have been 

 bored . After the test the necks of the bottles are placed in 

 the holes and the contents allowed to run out, giving each 

 bottle an occasional shake. The bottles, after their con- 

 tents have escaped, should be rinsed twice with very hot 

 water and then in a warm dilute solution of lye, soap 



