(rooeh and Beyer — Use of the Filtering Crucible. 251 



filtration. The liquid is drawn through the felt to the flask, 

 the chamber washed down, and removed from the crucible, 

 and the deposit is well washed. The crucible and contents 

 are dried and weighed, the increase over the original weight 

 being, of course, the weight of the deposit. 



In Table I are given the details of experiments made to 

 test this form and use of the apparatus. Copper sulphate 

 strongly acidulated with sulphuric acid was the electrolyte. 

 Deposition was completed in the times given and the ferrocyan- 

 ide test applied to the whole filtrate showed the absence of 

 copper in every case. The apparatus and deposit were washed 

 first with water and finally with alcohol. It was noticed that 

 though the filtrate contained no copper, the washings did 

 sometimes contain a bare trace. When the filtrate was allowed 

 to stand after treatment with potassium ferrocyanide it turned 

 blue rapidly, and this action, which indicated probably the 

 presence of hydrogen dioxide or of persulphuric acid produced 

 in the electrolysis of the sulphuric acid, is suggestive that the 

 liquid should be drawn from the deposit as quickly as may be 

 after the current is cut off. In experiments (1) and (2) no 

 special care was taken in this respect, and in these experiments 

 the results are a trifle higher than those of experiments (3) to 

 (7), in which the manipulation was quickly made. 



Table I. 



First Process : Electrolysis with filtration after interruption of the current. 

 Vol. Theory 



CuS0 4 .5H 2 of H 2 SO. ( for Copper 



taken liquid (1:1) Current Time copper found Error 



grm. cm 3 . cm 3 , amp. volt. min. grm. grm. grm. 



(1) 00538 50 5 | 4 ] V ] 40 °' 1283 0-1290* +0-0007 



(2) 0-0510 50 5 {4 | 7 j J) 0-1276 0-1282* +0-0006 



(3) 0-5009 50 5 " 4 j 7 j 40 O* 12 * 76 0*1279* +0-0003 



(4) 0-5005 50 5 \ 2 . i 5 H \ ,J 0*1275 0-1277* -J-0'0002 

 v ' { 4 ( 7 ( 40 



(5) 0-5047 50 5 \ 2 . \ I \ .J 0-1285 0-1286* +0-0001 



v ' I 4 ( 7 ( 40 



(6) 0-5039 50 5 j 4 j 7 ' j 40 ' 1283 0'1285* +0-0002 



(7)0-5030 50 5 "S4 )7 ] 40 °* 1281 0'1282f +0-0001 



* No copper in filtrate or in washings, 

 f Trace of copper in washings. 



