MACERATION METHOD. 121 



is transferred to a hot plate, and the paste mixed with the stirrer ; 

 at a certain point in the evaporation the paste comes away from 

 the basin, and by careful manipulation both basin and stirrer 

 can be obtained practically clean. On further evaporation and 

 stirring, the paste begins to get into a condition in which it can 

 be broken up and rubbed into pieces, and at this stage it is 

 removed from the hot plate and about 20 c.c. of methylated 

 ether (specific gravity 0-720) dried with calcium chloride are 

 added. On gentle rubbing with the stirrer the solids begin to go 

 to pieces ; the stirrer and basin are now scraped with 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 treated again 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 

 ground further ; the ether at this stage looks like whitewash, 

 and the solids take some minutes to subside sufficiently to allow 

 of decantation. After about six or eight treatments in this 

 manner the solids are allowed to air-dry, the portions clinging 

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

 alcohol and a few drops of water are added ; the solids are 

 well mixed with the alcohol, and the basin is placed on the 

 hot plate and evaporated till the paste begins to go to pieces, 

 when the solids are treated as before. A second treatment with 

 alcohol and a further six to eight extractions with ether are 

 given ; the filter gradually becomes partially blocked with the 

 finely-divided solids, but never to such an extent that filtration 

 stops. The solids are air-dried, and then dried in the water-oven 

 to constant weight (0-00428 gramme is subtracted for each c.c. 



N 

 of -^- strontia used). At the Government Laboratory the solids 



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

 Miller omit this ; although the solids not fat are hygroscopic, 

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

 known from previous weighings to within a very small amount, 

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

 more than a few tenths of a milligramme of hygroscopic moisture 

 are taken up during the weighing. The top of the filter where 

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

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



