12 



DEPARTMENT OF AGRICULTURE. 



sulphuric acid, break down, liberating carbon-dioxide gas, which, rising through the 

 fat column, gathers on its surface in the form of air-bubbles. If a few drops of 

 sulphuric acid are added to every half-pint of water that is to be added to the 

 bottles, this trouble may be avoided, or at least largely overcome. 



TESTING CREAM. 



In testing cream the principle is the same as in testing milk. Cream-test 

 bottles, with specially graduated necks to contain 30, 40, or 50 per cent, of the 

 quantity taken, are used. 



The varying thickness of cream, viscosity, specific gravity, and amount of air- 

 bubbles which it contains makes it almost impossible to obtain accurate or reliable 

 results in testing if the sample is measured with a pipette. The same weight of 

 cream as milk is necessary namely, 18 grams; but since cream has a less specific 

 gravity, or is lighter than milk, due to the larger proportion of butter-fat, it is neces- 

 sary to use more than 17.6 c.c. A pipette graduated to 18 c.c. 

 would be more nearly correct, and fairly accurate results can 

 be obtained by its use in testing cream which contains up to 

 about 25 per cent, of fat. Very rich, overripe, or gassy cream, 

 or cream fresh from the cream-separator, cannot be accurately 

 measured. Where strict accuracy is essential, as in the case of 

 creameries or dairies buying cream on a butter-fat basis, it is 

 necessary to weigh such cream on a very finely balanced scale. 

 For the purpose of testing cream on the farm, where sensi- 

 tive cream-scales are lacking, and where there is no particular 

 need of maximum accuracy, the cream may be measured into the 

 test-bottle by means of an 18-c.c. pipette instead of being 

 weighed. In this case, however, the pipette should be rinsed 

 with warm water and this also added to the test-bottle. If care 

 is used in making the test, the pipette method gives fully accu- 

 rate results. It should be understood, however, that the results 

 are only approximate, and are not entirely comparable with the 

 more accurate way of weighing the cream which is practised in 

 the creamery or city milk plant. 



"The other operations of the test are carried out the same as 

 in testing milk. The reading of the cream test should be from 

 to the bottom of the upper curve (meniscus) of the fat 



-A 



3 



Fig. 7. In reading 

 cream tests the fat 

 column should be 

 read from A to B. 



the extreme bottom 

 column. (Fig. 7.) 



TESTING SKIM-MILK AND BUTTERMILK. 



"/ 



Skim-milk and buttermilk are tested the same as whole milk, excepting that 

 a double-necked special test-bottle is used. As the amount of butter-fat in skim- 

 milk and buttermilk is small, it is necessary that the test-bottle have a neck in 

 which a very small amount of fat may be read in terms of per cent. The total 

 graduation of these bottles is usually 0.5 per cent., and the subdivisions represent 

 0.01 per cent. each. 



NOTE. In testing skim-milk or buttermilk, it is very necessary to have all the 

 glassware perfectly clean, as a slight amount of fat in the pipette or bottle would 

 seriously affect the results. 



WASHING THE TEST-BOTTLES. 



This is a very important consideration, as the slightest amount of fat left in 

 unclean bottles will affect subsequent tests, and may cause variations of 0.1 to 0.2 

 per cent, in the reading of the fat column. As soon as the tests have been recorded 

 the bottles should be emptied while still hot and before the fat has solidified in the 

 necks. Slinking the bottles while emptying them will aid in removing the scdinu-nl 



