452 Van Name — Sidphoeyaiiides of Copper and Silver 



In the experiments to be described this difficulty was avoided 

 by performing the filtering and weighing upon asbestos in a 

 perforated platinum crucible. The method of conducting a 

 determination was as follows : A suitable quantity of a 

 standard copper sulphate solution was run from a burette, 

 diluted to a convenient volume, a few cubic centimeters of a 

 saturated solution of ammonium bisulphite added, and the 

 copper precipitated by an excess of ammonium sulpliocyanide. 

 The precipitate was allowed to settle, collected upon asbestos 

 in a weighed crucible, washed with cold water and dried at 

 110° until no further loss of weight took place. 



In Table I are given the results of a number of determina- 

 tions made in this way. The copper sulphate solution was 

 made up exactly decinormal and the standard confirmed elec- 

 trolytically. As the ammonium sulpliocyanide solution was 

 slightly above decinormal, 13 om3 represent a small excess (about 

 one cubic centimeter) above the amount theoretically required 

 to precipitate 25 om3 of the copper sulphate solution. The ammo- 

 nium bisulphite, which had been recently prepared by satu- 

 rating aqueous ammonia with sulphur dioxide, was always used 

 in sufficient quantity to give the liquid a strong and permanent 

 odor of the latter. 









Table I. 









2 5cm3 f ]S3"/10 C 



uSO.i solution, equivalent to 0-0795 grm, 



Cu, taken for each 









experiment. 















NH 4 SCN 













H 2 S0 4 



HNH4SO3 



approx. 



Final 



Time of 



Cu 







concentrated. 



sat. sol. 



N/10. 



volume. 



standing. 



found. 



Error 





cm 3 . 



cm 3 . 



cm 3 . 



cm 8 . 



hours. 



grm. 



grm. 



1. 



none 



5 



13 



68 



JL 

 4 



0-0795 



o-oooo 



2. 



a 



3 



13 



66 



48 



0-0793 



— 0-0002 



3. 



u 



3 



25 



78 



1 



2 



•0-0796 



+ 0-0001 



4. 



a 



3 



25 



78 



12 



0-0796 



+ 0-0001 



5. 



15 



10 



13 



85 



12 



0-0792 



— 0-0003 



G. 



1-5 



8 



13 



105 



48 



0-0785 



— o-ooio 



7. 



1-5 



3 



25 



85 



4 



00783 



— 0-0012 



8. 



1-5 



5 



25 



85 



21 



0-0795 



o-oooo 



9. 



5 



5 



25 



85 



3 



0-0797 



+ 0-0002 



10. 



15 



HC1 



concentrated 

 cm 3 . 



10 



25 



115 



21 



0-0793 



— 0-0002 



11. 



10 



5 



25 



100 



20 



0-0795 



o-oooo 



12. 



25 



10 



25 



100 



28 



0-0784 



—o-ooii 



When there is no free acid present the time of standing 

 before filtration and the amount of the excess of ammonium 

 sulphocyanide are practically without effect, as experiments 1 

 to 4 of the table show. 



