148 EXPERIMENT STATION. [Jan. 



THE USE OF THE ZEISS IMMERSION KE- 

 FRACTOMETER IN THE DETECTION OF 

 WATERED MILK. 



BY P. H. SMITH AND J, 0. EEED. 



The campaign before the 1910 session of the Massachusetts 

 Legislature, for a change in the milk standard, brought promi- 

 nently to the public mind the question as to Avhether slightly 

 watered milk mi<>ht be detected and differentiated from normal 

 low-grade milk by methods available to the analytical chemist. 

 Li addition to the relative proportion of solids and fat, the index 

 of refraction of the milk serum, as determined by the Zeiss im- 

 mersion refractometer, has been advocated as a valuable aid in 

 the detection of added water. The details of this method were 

 perfected by Leach and Lythgoe -^ who claim, after careful inves- 

 tigation, that " if a milk serum is found with a refraction lower 

 than 39, it is safe to allege that the sample was fraudulently 

 watered, especially if, in addition to this, the solids not fat stand 

 below 7.3 per cent." 



In order to obtain further light on the subject we have made 

 a complete analysis of the milk from three herds, together with 

 the analysis of several samples systematically skimmed and. 

 watered. The analytical methods used were those advocated by 

 the Association of Official Agricultural Chemists, while for deter- 

 mining the refractive index the procedure given by Leach - was 

 adopted. The results follow in tabular form : — 



' Thirty-fifth annual report, Massachusetts State Board of Health , 1 903 , p . 483 ; Journal Amer- 

 ican Chemical Society, 1904, 26: 1195. 

 * Food Inspection and Analysis, Leach, p. 765, published by John Wiley & Sons, New York. 



