242 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



formula gives the most accurate results when compared 

 with gravimetric determinations. This formula is as 

 follows : 



Per cent, solids not ^=-1 X (100 -f) 2.5 

 S = specific gravity; f =per cent, of fat. 



The results obtained with this formula will not differ 

 more than 0.25 to 0.5 per cent, from those obtained by 

 the gravimetric method. A table prepared by Shaw and 

 Eckles, which renders it unnecessary to make the cal- 

 culation for each sample, will be found on pages 243 to 

 245. The Babcock formula determines the per cent, of 

 solids not fat, but this table gives the per cent, of total 

 solids ; it is a modification of one prepared by Dr. Bab- 

 cock. In the table the per cent, of total solids in any 

 given sample will be found at the intersection of the 

 column headed by the number representing the lactom- 

 eter reading (Quevenne degrees) and the line corre- 

 sponding to the fat per cent., provided the lactometer 

 reading is a whole number. If the lactometer reading is 

 not a whole number then the per cent, of total solids is 

 found for the whole number and to this is added the 

 fraction found opposite the decimal in the table for 

 " proportional parts." Take, for example, a sample of 

 milk with a lactometer reading of 33.5 and a fat per 

 cent, of 3.5. At the point where the column headed 33 

 and the line marked 3.5 per cent, fat intersect are the 

 figures 12.46. In the table for " proportional parts," 

 opposite the decimal .5 is the fraction .13. This added 

 to 12.46 equals 12.59, which represents the per cent, of 

 total solids. 



