36 W. H. ELLIS ON 



He gives the following formula for calculating the percentage of genuine milk in any- 

 given sample : — 



™, i r • -1. solids not fat + 100 

 The percentage of genuine milk = x-^ 



This process came into very general use among the Enalish public analysts, and 

 was commonly employed by most of them in 1874 when they fixed their limits. These 

 limits were as follows : " Milk shall contain not less than 9 per cent., by weight, of milk 

 solids not fat, and not less than 2'5 per cent, of butter fat." 



"Wanklyn's assertion that the percentage of solids not fat, in the unadulterated milk 

 of healthy cows, varies only within narrow limits, has been abundantly corroborated by 

 the thousands of analyses made since his work was published, and constitutes, as he 

 says, the fundamental fact of milk analysis. 



"Wanklyn and those who have followed him, are agreed that a milk analysis for the 

 purpose of detecting adulteration, essentially consists in the determination of the fat and 

 of the solids not fat. The second detects watering ; the first and second taken together 

 detects skimming. 



The solids not fat may be determined directly by weighing the dry residue after 

 exhausting the fat, or indirectly, by subtracting the weight of the fat from the weight of 

 the total solids. 



Wanklyn's method for the determination of the total solids leaves nothing to be 

 desired, except in the matter of the duration of the drying. In three hours, a milk residue 

 is not dry. The solids should be dried to constant weight. His method for fat extraction, 

 however, was defective. It is impossible, working according to his directions, to extract 

 all the fat. When 5 or 10 cc. of milk are dried on the water bath, the solids form a 

 horny mass, which is attacked by solvents only with great difficulty. On both these 

 points, namely, that milk is not dry in three hours at 100° C, and that the fat cannot all 

 be removed from a milk residue by boiling with ether, Mr. Hehner has given satisfactory 

 evidence {Analyst, 1873, VII. 160). 



Various methods and modifications have been introduced, by different analysts, to 

 meet these difficulties. With regard to the first, some chemists have dried at a higher 

 temperature than 100" C, and others have dried on the water bath to constant weight. The 

 latter of these methods gives trustworthy results, the former gives rise to partial decom- 

 position of milk solids. (Hehner, loc cit.) 



As to the fat extraction, one of the earliest really good methods is that of Baumhauer, 

 who ran from a pipette 10 cc. of milk into about 50 grams of quartz sand, contained in 

 a filter, dried, weighed, extracted with ether, and after driving off the ether, weighed 

 again. 



In the table, that comes at the head of page 37, the total solids and fat obtained by 

 myself from genuine milk, by Wanklyn's and Baumhauer's processes respectively, are 

 compared. 



The introduction of Soxhlet's apparatus for the extraction of fat had a marked 

 influence on milk analysis, and it has been largely adopted. By the use of this apparatus, 

 the quantity of fat that can be extracted from a milk residue is increased. 



I have been in the habit of using the following method : — Ten cc. of milk are run 



