MILK SUGAR 71 



use is T. S. = 1.2F+Q.25G. This is, with very slight modifi- 

 cations, the basis of Babcock's tables which are official in Amer- 

 ica. Richmond now prefers the formula T. S. = 1.2F+0.25(r 

 +0.14 and this was used in the preparation of the slide rule 

 which so greatly facilitates the calculation of the total solids 

 from the fat and specific gravity determinations. It is ad- 

 visable to remember that the differences between the results 

 obtained by use of the various formulae are within the limits of 

 experimental error and that a direct determination should be 

 made when great accuracy is required. 



Richmond's and Babcock's tables are given in the appendix 

 on pages 210-213. 



Solids Not-fat. These are estimated by deducting the per- 

 centage of fat from that of the total solids or they may be cal- 

 culated directly from the gravity and the percentage of fat. 



Milk Sugar. Milk Sugar, or Lactose, may be estimated by 

 either the polarimetric, volumetric, or gravimetric methods. 

 When a polarimeter is available, this method is almost invari- 

 ably employed as but little time is required for the examination 

 of several samples. In the absence of this instrument, and 

 when only occasional determinations are required, the gravi- 

 metric method should be used. 



Polarimetric Methods. These are based upon the exam- 

 ination of the milk serum in a polariscope after the separation 

 of the fat and proteids. A solution of mercuric nitrate, pre- 

 pared by dissolving mercury in twice its weight of nitric acid 

 (1.42) and diluting with an equal volume of water, is the most 

 suitable reagent for this purpose. As the removal of proteids 

 and fat reduce the volume of the lactose containing solution, it is 

 necessary to correct the readings for the percentages of these 

 constituents, but Richmond and Boseley (Dairy Chemistry) 

 point out that these calculations can be simplified by the use 

 of the following method. 



To 100 c.cms. of milk add 



(a) A quantity of water in c.cms. equal to ^ the lactometer 

 reading or excess gravity over 1000. 



