LACTOMETER AND ITS USE 79 
cent milk, but the specific gravity of a four per cent milk 
is practically the same as that of a four and one-half per 
cent milk. From what has been said about the relation- 
ship of the fat and solids not fat in milks of different 
richness, it is quite natural that the specific gravity of 
such milks should vary but little. If the fat alone were 
increased, the lactometer reading would naturally be de- 
pressed. But since the solids not fat increase in nearly 
the same proportion as the fat, the depression caused by 
the latter is compensated for by the former. 
Calculation of Milk Solids. The milk solids are cal- 
culated from the fat and the lactometer reading of milk. 
This is done by means of the following formula worked 
out at the Wisconsin Agricultural Experiment Station: 
Formula for solids not fat equals one-fourth L, R plus 
one-fifth F, in which L stands for lactometer, R for 
reading, and F for fat. Expressed in another way, the 
solids not fat are obtained by adding one-fifth of the fat 
to one-fourth of the lactometer reading. ‘The total solids 
are obtained by adding the fat to the solids not fat. 
Examples: 
1. To calculate solids not fat when the milk shows a 
lactometer reading of 31.6 and fat reading of 3.5. Sub- 
stituting these figures for the letters in the formula, one- 
fourth L, R plus one-fifth F, we get: 
31, 3.5 
3 plus =) equals (7.9 plus .7) equals 8.6 equa!s 
solids not fat. 
2. The total solids in the above sample are obtained 
by adding the fat and solids not fat. Thus: 8.6 plus 3.5 
equals 12,1 equals total solids, 
