STORCH METHOD. 123 



of the protein. The solids not fat obtained by the maceration 

 method are always more acid than the milk, and the aldehyde 

 figure is less, the increase of acid and the decrease in the aldehyde 

 figure being identical within the limits of experimental error. 

 These figures afford data for the estimation of the increase of 

 weight due to the condensation of the aldehyde, and assuming 

 that it is acetaldehyde, the error is almost constantly 0-03 per 

 cent, unless freshly-distilled aldehyde-free ether be used. 



Even this addition does not explain the whole of the difference 

 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 difference 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 

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



The Storch 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 percolated through it till no more fat was 

 extracted, the efher 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 was 

 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 using 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 been well extracted with ether previously, 

 or to a 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 



