MILK TESTS 449 



skimmed milk. In connection with the Babcock test, the lactometer 

 is most valuable, and several formulae are in use by which the solids 

 not fat or the total solids of milk may be closely computed from the 

 specific gravity and the fat test. 



The lactometer is a form of hydrometer adapted especially for use 

 in milk. Several styles are in use, the Quevenne being the most con- 

 venient because its readings indicate the specific gravity without the 

 necessity of more than a simple mental calculation. The readings 

 on the stem of the Quevenne lactometer are from 15 to 40, and they 

 represent the second and third decimal figures of the specific gravity, 

 the preceding figures always being 1.0 ; thus, a reading of 29 represents 

 a specific gravity of 1.029. This instrument should be used in milk 

 at a temperature of 60° F. If the temperature varies therefrom, a cor- 

 rection of the reading must be made, .1 of a lactometer degree being 

 added to the reading for each degree of temperature of the milk above 

 60° F. or if the temperature is below 60° F, .1 of a lactometer degree 

 is subtracted from the reading for each degree of temperature of 

 the milk below 60° F. Thus, if the lactometer reads 31 at a tem- 

 perature of 65° F., the corrected reading for 60° F. would be 31.5, and 

 the specific gravity of this milk at 60° F. would be 1.0315. Special 

 tables for making corrections for different temperatures are published 

 in books treating on the subject. Bj^ the rule given, it is not advis- 

 able to attempt to correct for a variation of more than 10° from 60° F. 



Another style of lactometer in common use is know^n as the New 

 York Board of Health lactometer. Its graduations are from 10 to 120. 

 The instrument stands at 100 in milk having a specific gravity of 1.029, 

 and it would stand at 0, if graduated to that point, in a fluid having a 

 specific gravity of 1. Thus, 100° in the B of H lactometer equals 29° 

 on the Quevenne lactometer, and it is a simple matter to compute the 

 equivalent reading of one lactometer for any given reading on the other 

 by the formula : — 



Q = .29BofH, orBof H = -^. 



.29 



Test for boric acid or borax used as preservatives (Van Slyke). 



Add lime-water to 25 cc. of milk until the mixture is alkaline to phe- 

 nalphthalein ; evaporate to drj'ness and burn to an ash in a small por- 

 celain or platinum dish. Add a few drops of dilute hydrochloric acid 

 2a 



