DETERMINATION OF SOLIDS 217 



subtracted, one gets the quantity of solids not fat. By 

 incinerating tlie contents of the vessel, in a muffle oven, 

 and again weighing, the amount of salts, or ash, is deter- 

 mined. If it is desired to extract the fat from the other 

 solids, to determine the fat percentage, it is necessary 

 before drying the milk to mix with it a weighed quantity 

 of roasted pumice stone ; then, after evaporation, the fat 

 is removed by means of ether (or benzine) in an ordi- 

 nary fat extraction apparatus, and is determined by 

 weighing, after evaporating the ether. This work is 

 quite particular and requires a well appointed labora- 

 tory. Moreover, in practical milk control, gravimetric 

 analyses are not indispensable, for one can easily cal- 

 culate the quantity of solids from the specific gravity 

 and the fat, according to the formula derived by Fleisch- 

 mann. If total solids are represented by t, the fat per 

 cent, by f and the specific gravity by s, one has : 



= :.2 X f + 2.665 X 



That is, if we say f = 3.55 and s z= 1.0327, we get 



100 X 1.0327 - 100 \ Anan , 2.665 X 3.27 



t - 1.2 X 3.55 + (2.665 X 10 * ^ ~ 10 ) = 4- 



4.260 + 





Another formula proposed by Bertschinger gives quite 

 accurate results : 



Moreover, tables have been worked out from which 

 the total solids can be read off, if both the other factors 

 are known. Ackermann has constructed an ' ' automatic 

 reckoner " from which one can read off one of the fac- 

 tors when both of the others are known, by simply turn- 

 ing circular discs. [Richmond has devised a sliding rule 

 for the same purpose.] 



The computation of the solids not fat is very easy. 



