RITTHAUSEX METHOD. 129 



sugar, etc., and drying, the fat may be extracted with ether ; or a 

 little strong alcohol may be poured on the precipitate to remove 

 water, after which ether will extract the fat ; the ethereal and 

 alcoholic solutions are evaporated together and the fat weighed. 



The fat may be extracted similarly from the casein precipitated 

 by the addition of acetic acid to the diluted milk. 



The results agree well with the Adams method, except in the 

 case of very highly skimmed milks, when there is a tendency to 

 be low. 



This method has the advantage that the fat can be determined 

 on the same portion of milk used for the estimation of proteins 

 and milk-sugar. 



The following comparative figures will show the results which 

 may be expected : 



Fat by Ritthausen, . 4-93 2-87 1-38 4-00 0-04 

 Fat by Adams, . . 4-97 2-89 1-43 3-99 0-17 



Harrison and Goodson, working in the author's laboratory, 

 have shown that this method cannot be used for the estimation 

 of fat in sterilised or condensed milks, nor is it available for 

 homogenised milk. 



Other Methods of Gravimetric Pat Determination. The 

 other methods for the estimation of fat in milk are very numerous ; 

 a few of those which have been proposed may be noticed briefly. 



Wanklyn's method consists in extracting the fat from the 

 solids of milk dried per se. The totality of the fat is never 

 obtained, as, owing to the hard, horny character of the residue, 

 a considerable proportion of the fat is protected from the ether. 

 This method attained considerable notoriety, owing to its semi- 

 official adoption by the Society of Public Analysts more than 

 forty years ago, but has now fallen into almost complete dis- 

 use. It has been modified by stirring the residue during evapo- 

 ration to obtain a more granular residue, and by evaporating 

 in a conical flask to expose a large surface to the ether, but the 

 results, even with these modifications, have been unsatisfactory. 



Hoppe-Seyler and, later, Liebermann have proposed shaking 

 the milk with potash (to. dissolve the casein), and then extracting 

 with ether, but the separation of the ether is so slow as to render 

 this method impracticable. 



Morse, Piggott, and Burton add the milk to anhydrous copper 

 sulphate, which combines with the water, giving a dry residue 

 at once ; they then extract with petroleum ether. 



Baynes proposes drying the milk on powdered glass, a method 

 essentially the same as that of Storch. Sand has also been 

 used in Germany ; but as it is very difficult to grind this up, its 

 use is not to be recommended. 



9 ' 



