Gooch and Heath — Iodometric Determination of Copper. 71 



So it appears that a trifling amount of iodine is in every case 

 set free, due no doubt to presence of traces of iodate. It 

 appears also that no more than 2 cm3 of concentrated sulphuric 

 acid or hydrochloric acid may safely be present with 2 grms. 

 of potassium iodide in 50 cmS of solution, and the presence of 

 l cma of pure nitric acid makes error. The tendency to liberate 

 iodine is manifestly less at the higher dilution, and it appears 

 that in a volume of 100 cn ' 3 of solution containing 5 grms. of 

 potassium iodide 3 om3 of concentrated sulphuric acid, hydro- 

 chloric acid or nitric acid free from nitrogen oxides may safely 

 be present. Acetic acid of 50 per cent strength may apparently 

 make up half the solution at either dilution. When either 

 sulphuric acid, hydrochloric acid or nitric acid is present, 

 obviously the higher dilution is preferable. 



Following are the results of experiments in which various 

 amounts of copper were determined by titration of the iodine 

 set free in a volume of 100 cm3 in presence of 5 grms. of potas- 

 sium iodide and free acid. 



Table IV. 



Effects of 



Acids 



upon the Determination of Sin 



all Amounts 







of Copper. 







Copper 











\ 



taken 







Total 



Copper 





as Cu(N0 3 ) 2 



KI 



Acid 



volume 



found 



Error 



grm. 



grm. 



cm 3 . 

 H 3 S0 4 cone. 



cm 3 . 



grm. 



grm. 



o-ooio 



5 



1 



100 



0-0016 



+ 0-0006 



o-ooio 



5 



2 



100 



0-0014 



+ 0-0004 



o-ooio 



5 



3 

 HC1 cone. 



100 



0-0019 



+ 0-0009 



o-ooio 



5 



1 



100 



0.0014 



+ 0-0004 



o-ooio 



5 



2 



100 



0-0014 



+ 0-0004 



o-ooio 



5 



3 



HN0 3 cone, 

 purified 



100 



0-0015 



+ 0-0005 



o-ooio 



5 



1 



100 



0-0014 



+ 0-0004 



o-ooio 



5 



2 



100 



0-0015 



+ 0-0005 



o-ooio 



5 



3 



HC 2 H 3 2 . 

 50 per cent 



100 



0-0015 



+ 0-0005 



o-ooio 



5 



10 



100 



0.0012 



+ 0-0002 



o-ooio 



5 



20 



100 



0-0012 



+ 0-0002 



60010 



5 



30 



100 



00010 



±0-0000 



o-ooio 



5 



40 



100 



0.0010 



±0-0000 



o-ooio 



5 



50 



100 



o-ooio 



±0-0000 



It appears that so much as 50 om3 of 50 per cent acetic acid may 

 be present with 5 grms. of potassium iodide in 100 cm3 of solution 



