112 



ANALYSIS OF MILK. 



with water, shaking the washed ether with calcium chloride, 

 and, after allowing it to stand over calcium chloride for a day or 

 two, distilling. 



Ether sufficiently pure for most purposes may be obtained by 

 distilling (from a water-bath not exceeding 40° C. in tempera- 

 ture) the commercial product from a flask to which a fractionating 

 column is fitted. The first fractions boiling below 34:-3° C. and 

 the last boiling above 34 '8° C. should be rejected. 



The following figures show the amount of difference that may 

 be expected between the two modes of procedure : — 



Percentage of Pat. 



The average difference is found to be 0-06. 



The Maceration Method (often called the Somerset 

 House Method). — Dr. James Bell, when Principal of the Inland 

 Revenue Laboratory at Somerset House, on being appointed 

 referee under the " Sale of Food and Drugs Act," devised this 

 method for the estimation of fat and solids not fat in mUk, and 

 it has since been perfected at the Government Laboratory. 



The following details of procedure are those employed by the 



author and Miller, and are essentially those of the Government 



Ijaboratory : — About 10 grammes of milk are weighed into a 



basin of platinum or aluminium about 3 inches in diameter and 



a little over 1 inch high, with a flat bottom, provided with a 



(lat-ended glass stirrer. Two drops of a 0'5 per cent, solution 



N 

 of phenolphthalein are added, and approximately :pj- strontia 



solution run in till a faint pink colour appears. The contents 

 are evaporated to a damp paste on the water-bath, when the basin 

 is transferred to a hot plate, and the paste mixed with the stirrer ; 

 at a certain point in the evaporation the paste comes away from 

 the basin, and by careful manipulation both basin and stirrer 

 can be obtained practically clean. On further evaporation and 

 stirring, the paste begins to get into a condition in which it can 

 be broken up and rubbed into pieces, and at this stage it is 

 removed from the hot plate and about 20 c.c. of methylated 

 ether (specific gravity 0'720) dried with calcium chloride are added. 

 On gentle rubbing with the stirrer the solids begin to go to pieces ; 



