90 



FORMULAE FOR CALCULATIONS. 



Fig. 9. 

 Milk Scale. 



end of the specific gravity scale then gives the 

 fat as calculated by the formula 



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



To facilitate reading, Cassal and Gerrans 

 propose adding 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 necessary, the error due to 

 unavoidable circumstances being greater than 

 the error of computation of the hundredths. 



Tables for Calculation. Table XVIII. is 

 for the calculation of solids not fat to 2 places 

 of decimals by the author's formula. The 



c* 

 values of 0-2625 = can be found by means of 



the first part of the table, including the difference 

 table, for each 0-1 from 22-0 to 37-5, and 

 in the second part of the table the values of 

 0-2 F. are given. The two values are added 

 together to give the solids not fat. In the 

 difference table, if the fat is up to 0-02 above 



