MILK FORMULAE. 89 



gravity from 1-0320 did not give results which agreed well with* 

 the formula, various approximations have been made to this. 



The author has calculated a formula which gives practically 

 the same results, but is more scientifically correct, and which 

 does not require the application of approximations. This is 



T = 0-262^ + M7F. 



As the previous formulae were deduced from analyses to which 

 objection could be taken, the author has deduced a new formula 

 from the results of analyses made as exactly as possible. 



T = 0-2625^ + 1-2F. 



This has been found to be expressed by the simpler formula 



c* t\ 



T== + -F + 0-14 within very small limits if the specific 

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gravity lies between 1 -020 and 1 -036. 



Fleischmann has recently given the approximation formula 



T = j + 1-2 F + 0-25 ; the formula S.n.R = --^ gives a 



fair approximation with average milks. 



p* fi 



The formula T = - + - F also approximates closely to that 

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of Hehner and the author. 



Other formulae have been devised by J. C. Brown, Babcock, 

 Leonard, and others. 



Of the above formulae, that of Fleischmann agrees best with 

 the results when Soxhlet's method of fat estimation is used ; 

 that of Hehner and the author when the Society of Public 

 Analysts' methods are employed ; while if the methods mentioned 

 later as most exact in the author's opinion be employed, the 

 author's formula gives the most satisfactory results. 



The fat calculated from the specific gravity and total solids 

 almost invariably agrees within 0'2 per cent, with the determina- 

 tion made by the appropriate method. 



Milk Scale. In order to save calculation the author has 

 devised a slide rule, known as the " milk scale " (Fig. 9), from 

 which the percentage of fat can be read off directly from the 

 specific gravity and percentage of total solids. On one side a 

 scale is placed indicating total solids, 1 per cent, of total solids 

 being represented by 1 inch ; on the other side the fat is shown 

 by a scale of 1-2 (14 inches) to 1 per cent. ; the slide carries 

 the specific gravity scale, 1 being equal to 0-25 (J) inch. The 

 line indicating the specific gravity found is placed against the 

 total solids estimated ; an arrow placed 0-14 (I) inch from the 



