ESTIMATION OF FAT — STORCH METHOD. 115 



between the maceration and Society of Public Analysts' methods, 

 and the marked browning of the residue in the latter method 

 suggests that the remainder of the difEerence is due to the results 

 obtained by it being too low ; this conclusion is strengthened 

 by the fact that evaporation over a large surface, whereby brown- 

 ing of the residue is avoided, gives slightly higher results. 



The Storoh Method. — The essential point of this method 

 consists in drying the milk on pumice (or other medium) and 

 extracting with ether after finely grinding in a mortar. 



As originally designed by Storch, 10 grammes of milk were 

 dried at 100° C. on about an equal weight of pumice in pieces 

 about the size of a small pea ; the pumice was ground in a mortar 

 to a very fine powder, which was then transferred to a conical 

 tube, and ether allowed to percolate through it till no more fat 

 was extracted, the ether being received in a tared flask. The 

 pumice was removed and reground, and percolation again con- 

 tinued ; and this treatment was repeated till no more fat \\'as 

 extracted. The method was somewhat tedious, though very 

 exact. 



Kieselguhr Method. — In order to avoid the troublesome 

 grinding of a hard substance like pumice and to economise time, 

 the author prefers to use kieselguhr in place of pumice ; the 

 method is performed as follows : — 



About 3 or 4 grammes of ignited kieselguhr or fossil meal are 

 placed in a porcelain basin, a cavity being made in the centre, 

 and 10 grammes of milk allowed to flow in, care being taken 

 that none is permitted to fall on the sides of the basin. The 

 kieselguhr is dried on a gently-boiling water-bath, being stirred 

 at frequent intervals as drying proceeds ; after about an hour's 

 ■drying the kieselguhr can be powdered in the basin with a small 

 pestle. The powder is transferred to a wide test tube, with a hole 

 at the bottom, containing a half-inch plug of cotton wool, which 

 has previously been well extracted with ether, or to a Schleicher 

 and Scliull's thimble ; both basin and pestle should be scraped, 

 and the basin should be rinsed two or three times with kiesel- 

 guhr, the pestle being used to grind up the rinsings with any 

 portions adhering to the sides. The rinsings are added to the 

 tube, and a circular piece of filter paper, of such size as to fit 

 the tube, placed over the kieselguhr. The tube is placed in a 

 Soxhlet extractor and extracted with ether for three hours ; 

 •care must be taken that the top of the tube is well above the 

 top of the siphon and that the ether is not distilled at such a 

 rate that it fills and overflows the upper portion of the tube. 

 After three hours' extraction the tube is removed from the 

 ■extractor, the kieselguhr emptied out into the basin, and, after 

 allowing the ether to evaporate, again powdered, and re-extracted 



