Gooch and Heath — lodometric Determination of Copper. 73 



Table V (continued). 



KI Volume 



Copper Approx- at begin- at end 



taken as Pres- imate ning of of titra- Copper 



Cu(N0 3 ) 2 ent excess Acid titration tion found Error 



grni. grm. grm. cm 3 . cm 3 . cm 3 . grm. grm. 



B 

 Final volume between 140 cm3 and 155 cm3 without increase of KI. 



0-3336 5-0 3-5 H 2 S0 4 100 153 0-3315 —0-0021 



o 



0-2818 5-0 4-0 H^ 1 100 144 0-2797 — 0'0021 

 0-3320 5-0 3-5 HN0 3 100 152 0-3290 — 0'0030 



0-2541 



5-0 



3-5 HC 2 H 3 2 100 140 0-2523 —0-0018 





Final 



volume increased to 132 cm3 and 150 cm3 , 

 with corresponding increase of KI. 





0-2218 

 0-3231 



7-0 

 8-0 



6-0 

 6-4 



H 2 S0 4 

 cone. 



2 

 3 



100 

 100 



135 

 150 



0-2214 

 0-3226 



— 0-0004 



— 0-0005 



0-2023 

 0-2581 



7-0 



7-8 



6-0 

 6-7 



HC1 



cone. 



2 

 3 



100 

 100 



132 

 141 



0-2016 

 0-2574 



— 0-0007 



— 0-0007 



0-2023 

 0-2520 



8-0 

 10-0 



7-0 



8-5 



EN0 3 cone, 

 purified 



1 

 3 



100 

 100 



132 

 148 



0-2017 

 0-2512 



— 0-0006 



— 0-0008 



\ 



0-2125 

 0-2064 



7-5 

 8-0 



-- 



HC2H3O2 

 50 per cent 



5 



8 



100 

 100 



133 

 132 



0-2119 

 0-2058 



— 0-0006 



— 0-0009 



The N/10 sodium thiosulphate used in estimating the iodine 

 liberated added appreciably to the initial volume, 100 em3 , of 

 the solution. In series A the increase of volume, less than 

 20 cm3 , did not affect appreciably the accuracy of the determi- 

 nations. In series B the increase of volume to 140 cm3 , without 

 corresponding increase in the amonnt of potassium iodide 

 present, did affect the indications unfavorably. 



In series C, however, the unfavorable effect of similar dilution 

 was overcome by the addition of more potassium iodide. 



It is apparent that at any volume a very considerable excess 

 of potassium iodide above the theoretical equivalent involved 

 in the reaction is necessary, and that the necessary excess 



