ESTIMATION OF FAT — MACERATION METHOD. 113 



the stirrer and basin are now scraped witt a knife or spatula to 



bring any small portions of solids adhering to the sides under the 



ether, and the solids are gently rubbed to a powder. The ether 



is decanted through a weighed filter 9 cm. in diameter, and the 



solids again treated with ether. The solids at this stage are in 



a condition in which they can be ground up to a fine powder ; 



the ethereal solution is allowed to settle, and the ether decanted 



through the filter ; without any further addition of ether the 



solids are now ground to a very fine powder. It is advisable to 



do this with only a very little ether in the basin, as it is then 



easy to see the larger portions which can be ground up one by 



one. A further addition of ether is made, and the solids further 



t;iouiid ; the ether at this stage looks like whitewash, and the 



solids take some minutes to subside sufficiently to allow of de- 



cantation. After about six or eight treatments in this manner 



the solids are allowfd to air-dry, the portions clin^'iiig bi the 



stirrer and sides of the basin scraped down, ami 5 c.c. of alcohol 



and a few drops of water are added ; the solids aic well mixeil 



with the alcohol, and the basin is placed on the hot plate and 



e\'aporate(l till the paste bei^ins to t^o to pieces, when the solids 



arc a^ain treatecl as liefore. A second treatment with alcohol 



and a further six to eight extractions with ether are f,fiven ; 



the filter gradually becomes partially blocked with the linelv- 



divided solids, but never to such an extent tliat filtration stops. 



The solids are air-diied, and then dried in tlie water-oven to 



constant weij^ht (()()()i28 graninie is subtractetl for each c.c. of 



N 

 - stiiiutia used). At the Govenunent Laboratorv the solids 



not fat are transferred to a weighing bottle, but the author and 

 ;\liller omit this; although the solids not fat are hydroscopic, 

 no appreciable error is due to this omission. The final weiiiht is 

 known from previous weighings to within a very small amount, 

 ami consequently the time of weighing is very short, and not 

 niiu'e than a few tenths of a inilligraninie of hyi;roseopic moisture 

 are taken up during the weii^hing. The top of the filter where 

 fat collects is cut off and cut into pieces and thoroughly washed 

 with ether ; the knife or spatula is wiped on some of the pieces 

 cut off to remove any particles of solids, and the filter containing 

 the pieces cut oft" is placed in a weighing bottle and dried in the 

 water-oven to constant weight. The ether is distilled, and the 

 residue of fat weii^hed ; the fat is extracted mth petroleum 

 ether, and the small residue insoluble in this solvent subtracted 

 from the weight ; this usually consists of phenolphthalein, and 

 its weight inav be iieulected without appreciable error. 



/■Estimation of Fiit in Firt:h Milk. — It has been shown by Thorpe, 

 and by the author, in conjunction with Hehner and Bevan, and 



