TOTAL PROTEIDS. 35 



The reaction should be tested on a drop of the clear 

 liquid, withdrawing it by means of a rod, taking care 

 not to include any solid particles. When the operation is 

 correctly performed, the precipitate which includes the 

 fat, settles quickly, and carries down all of the copper. 

 It is washed by decantation with about 100 c. c. of wa- 

 ter, and collected on a filter (previously dried at 265 F 

 and weighed in a weighing bottle). The portions adher- 

 ing to the sides of the beaker are dislodged with the 

 aid of a rubber-tipped rod. The contents of the filter 

 are washed with water until 250 c. c. are collected, 

 which are mixed and reserved for the determination of 

 the sugar as described below. The water in the pre- 

 cipitate is removed by washing once with strong al- 

 cohol, and the fat by six or eight washings with ether. 

 The Soxhlet apparatus may be used for this purpose. 

 The washings being received in a weighed flask, the 

 determination of the fat may be made by evaporating 

 the ether with the usual precautions. 



The residue on the filter, which consists of the pro- 

 teids in association with copper hydroxid.is washed with 

 absolute alcohol which renders it more granular, and 

 then dried at 265 F. in the air bath. It is weighed in 

 a weighing bottle, transferred to a porcelain crucible, 

 incinerated, and the residue again weighed. The 

 weight of the filter and contents, less that of the filter 

 and residue after ignition, gives the weight of the pro- 

 teids. The results by this method are slightly high, 

 owing to the fact that the copper hydroxid does not 

 become completely converted into copper oxid at 265 



