i8o The Analysis of Dairy Produce [303 



solution, so that its specific gravity is lower at the instant of 

 drawing than four or five hours later. 



Allowing for this source of error, there is a very definite 

 relationship between the specific gravity ar$ the chemical 

 contents of the milk. Qualitatively, an increase in the fat or 

 cream lessens the specific gravity, whilst an increase in the 

 solids not fat renders the specific gravity higher. 



Quantitatively this variation of the specific gravity has 

 been used to check the accuracy ot analysis, and also to 

 give a rapid and fairly accurate estimate of the percentage 

 of fat. 



It will be seen from the later paragraphs in this chapter 

 that the estimation of fat is the most difficult operation in the 

 commercial analysis of milk; if, therefore, the exceedingly simple 

 operations of estimating the total solids (paragraph 303) and 

 the specific gravity will give a correct idea of the percentage of 

 fat, much work may be saved. 



Richmond's formula is as follows : 



F=o*859T-o-2i86G, 



where F represents the percentage of fat, T the percent- 

 age of total solids, and G is the lactometer degree (i.e., the 

 number by which the specific gravity of the milk exceeds that 

 of water (water = I'ooo). 



This formula is based on the fact, first worked out by 

 Clausnizer and Mayer, that every addition of 1 per cent, of fat 

 decreases the specific gravity of milk by *ooi, whilst every 

 addition of 1 per cent, of solids not fat increases the specific 

 gravity by -00375. 



303. Total Solids. — Measure out accurately into a 

 weighed platinum dish 25 c.c. of milk which has been well 

 shaken up ; add two drops of strong acetic acid, and evaporate 

 to dryness on the water bath. Transfer to the steam oven, and 



