70 ANALYSIS OF MILK. 



gravity found is placed against the total solids estimated ; an 

 arrow placed 0-14 (|) inck from the end of the specific gravity 

 scale then gives the fat as calculated by the formula. 

 T = 0-25 Q + 1-2 F + 0-14. 



To facilitate reading, Cassal and Gerrans propose to add two 

 sliding pointers, one on the total solids scale, and one on the 

 specific gravity slide, which are first placed against the part of 

 the scales corresponding to total solids and specific gravity found 

 respectively, and the two pointers are then adjusted. This 

 arrangement prevents the possibility of error in adjusting the 

 slide. 



The author has also employed a runner made out of a piece of 

 brass bent round the milk scale, in which two holes are cut, 

 leaving a narrow bar between them ; this bar partially covers 

 both the total solid and specific gravity scales, and has a fine 

 line drawn upon it at right angles to the scales. By adjusting 

 this line to the total solids, and the specific gravity to the line, 

 the object sought by Cassal and Gerrans is attained. Stokes uses 

 a strip of transparent celluloid on which a fine line is drawn. The 

 idea of the runner is due to Lieutenant Mannheim of the French 

 Artillery, who, in 1851, devised it for a logarithmic slide rule. 



The scales are divided into tenths, hundredths being estimated 

 by the eye ; a decimal scale, or, better, a vernier, as suggested 

 by Sykes, can be applied to the runner, rendering it easier to 

 read the second place of decimals. This, however, is not neces- 

 sary, the error due to unavoidable circumstances being greater 

 than the error of computation of the hundredths. 



Tables are given from which the fat calculated from different 

 percentages of total solids and specific gravities can be read off. 



By our definitions (p. 58) 



»- 1 , , /-I 

 " and h — - 



n / ' 



and from the values given above in the formula mentioned, 

 a and h can be calculated. 



Thus, taking the formula T = 0-2625 ^ + 1-2 F, 



ar-'d y=0-9.;o ,, „ fat. 



