COMPOSITION AND PROPERTIES OF MILK 297 



for all values ; and if any two are known, the third can be 

 found. 



The specific gravities (lactometer degrees) are plotted on 

 the axis x'x, the figures to the right of the point of origin being 

 -h, and those to the left . The percentages of solids are 

 plotted on the axis_/j, the non-fatty solids on the +, or upper, 

 side of the specific gravity line, and the fat on the , or lower 

 side. The two graphs OA and OB represent the relation 

 between the specific gravities and the percentages of fat and 

 of non-fatty solids respectively. 



If there were no fat in the milk, + 36 of the lactometer 

 would correspond to 9 per cent, of non-fatty solids. Similarly, 

 if there were no non-fatty solids, 4 would correspond to 

 5 per cent, of fat. Therefore the specific gravity of a sample 

 of milk which contains 9 per cent, of non-fatty solids and 

 5 per cent, of fat would be [36 4 =] 32. Or, if the milk 

 contains 9 per cent, of non-fatty solids, and has a specific 

 gravity of 32, the difference between this number and 36 

 which corresponds to 9 per cent, of non-fatty solids is 

 [3 2 36 =] 4, which corresponds to 5 per cent, of fat. 

 Again, if the milk contains 5 per cent, of fat, and has a 

 specific gravity of 32, the sum of this number and 4 which 

 corresponds to 5 per cent, of fat is [32 + 4 =] 36, which 

 corresponds to 9 per cent, of non-fatty solids. 



The next diagram (Fig. 24) is similar to the preceding 

 one, but the axis y'y is not shown. The percentages of fat 

 and non-fatty solids are marked on the graphs OA and OB, 

 respectively, instead. The former, OA, is inclined to the right 

 instead of to the left, and in order to enlarge the scale, all 

 below 5 per cent, of non-fatty solids is omitted. A pointer F 

 is affixed to the line x'x at the point of origin (o per cent, of 

 fat), and there is another, N, which can also be affixed to x'x 

 at any given specific gravity. This arrangement enables the 

 calculation to be made in a purely mechanical manner, as 

 follows : 



Suppose a sample of milk to contain 3 per cent, of fat, and 

 that it has a specific gravity of 31 '6. To find the percentage 

 of non-fatty solids, let the pointer N be affixed to x'x at the 



