220

QUANTITATIVE AGRICULTURAL ANALYSIS

skim milk, the latter obtained by separating the cream with a
centrifugal separator.
table XVII.—comparative compositions of milk,   cream and skim
milk

	Fat 	Ash 	Casein 	Lactose 	Total
solids 	Specific
gravity 	
Milk              	 	5.0 	0.79 	3.50 	4.70 	14.0 	1.032 	
Cream           	 	21.9 	0.58 	2.02 	3.32 	27.0 	1,015 	
Skim milk 	0 2 	0 78 	3.62 	5.05 	9 6 	1 034 	
							
Fat.—The Babcock bottle used for testing milk is not suitable
for cream on account of the higher proportion of fat. If the
cream were 25 per cent fat, 18 gm would contain 4.5 gm of pure
fat. Assuming 0.9 as the average specific gravity of butter fat,
it will be seen that 5 cc of space would be required for the fat.
Various forms of bottles are used for this purpose, one of which is
shown in Fig. 48.
Either 9 or 18 gm of cream is weighed into the counterpoised
test bottles. Fat is determined by the Babeock" method as used
for rnilk, described on page 208; with the exception of the method
for reading the position of the upper end of the fat column. First
determine the value of the upper meniscus (in per cent) between
the extreme upper and lower points of the curve. Add one-third
of this value to the reading of the lowest part of the curve and
consider this the final reading.1
The fat column may be read more easily by adding a light
mineral oil which has been colored red with a vegetable pigment.
There are several such preparations on the market under trade
names such as "glymol," "alboline77 and "red top/7 The use
of a colored mineral oil was suggested after extensive investigation
of various compounds.2 If such an oil has practically the same
surface tension as that of melted butterfat the surface divid-
ing the two liquids is approximately plane. While the use of
such a device for making easier readings has become quite
1 hunziker, Ind. Exp. Sta. Bull, 146 (1910).
.   *Ibid.