Arsenic Acid. 



153 



the following table. The solution of potassium iodide was 

 diluted as indicated before the addition of the acid and the 

 iodine set free was titrated by thiosulphate. 









Na 2 S 2 3 

 added at 



Na 2 S 2 3 

 added after 



Na 2 S 2 3 



added after 



stirring 5 



HCl 

 Sp. gr. 1-16 

 taken. 



KI 

 taken. 



Total 

 volume. 



once. In 



terms of 



H 3 3 AsO. 



5 minutes. 



In terms of 



H 3 3 AsO. 



minutes. 

 In terms of 

 H 3 3 AsO. 



cm 3 . 



gm. 



cm 3 . 



gm. 



gm. 



gm. 



25 



2 



50 



0-0013 







25 



2 



75 



0-0004 







25 



2 



50 





0-0035 





25 



2 



75 





0-0019 





25 



2 



50 







0-0042 



25 



2 



75 







0-0021 



50 



2 



100 



0-0017 







50 



2 



150 



0-0004 







50 



2 



100 





0-0035 





50 



2 



150 





0-0019 





50 



2 



100 







0-0035 



50 



2 



150 







0-0014 



The proportionate strength of acid and the time before titra- 

 tion are, obviously, the essential factors. The absolute amount 

 of acid present and the stirring seem to make little difference. 

 As to the action of the hydrochloric acid on small amounts 

 of the thiosulphate, we have the evidence of the experiments 

 detailed in the following statements, in which 1, 2, and 5 cm3 of 



nearly — thiosulphate are exposed to the action of 25 cm3 



hydrochloric acid, sp. gr. 1\L6, without dilution or diluted with 















Iodine 













Iodine to 



Error of 



to color 



Error of 









Na 2 S 2 3 



color 



titration 



after 



titration 









i n 



without 



without 



diluting 



after 









nearly — 



dilution 



dilution 



to 15™ S 



dilution 



HCl 



Volume 





in terms 



in terms 



in terms 



in terms 



in terms 



Sp. gr. 



before 





of 



of 



of 



of 



of 



1-16. 



titration. 





H 3 3 AsO. 



H 3 3 AsO. 



H 3 O 3 As0. 



H 3 3 AsD. 



H 3 3 AsO. 



cm 3 . 



cm 3 . 



cm 3 . gram. 



gram. 



gram. 



gram. 



gram. 



25 



26 



1 



0-0071 



0-0062 



—0-0009 



0-0071 



o-oooo 



25 



50 



1 



0-0071 



0-0071 



o-oooo 



0-0071 



00000 



25* 



50 



1 



0-0071 



0-0079 



+ 0-0008 



0-0079 



+ 0-0008 



25 



50 



2 



0-0141 



0-0146 



+ 0-0005 



0-0146 



+ 0-0005 



25* 



50 



2 



0-0141 



0-0157 



+ 0-0016 



0-0157 



+ 0-0016 



25 



30 



5 



0-0353 



0-0336 



— 0-0017 



00374 



+ 0-0024 



25 



50 



5 



0-0353 



0-0359 



+ 0-0006 



0-0359 



+ 0-0006 



25* 



50 



5 



0-0353 



0-0411 



+ 0-0058 



0-0411 



+ 00058 



*In 



these exper 



imei 



its the acid 



stood in contact with the 



thiosulphati 



3 5 minutes 



before titration. 



