1896.] 



Hypochlorites to Chlorates. 



73 



It is evident from the above table that results from operations 

 (a) and (6) differ to a small extent, about 1 to i"5 °/ Q . The cause of this 

 disagreement has not been investigated. 



Most of the methods described above give the available chlorine 

 in a mixture of chlorate and hypochlorite. Direct titration by potas- 

 sium iodide and dilute acid originally introduced by Bunsen, but modi- 

 fied by Wagner, is said to give chlorine of the hypochlorite even in 

 presence of chlorates. Experiments prove the contrary. In fact, tacit 

 assumption of the accuracy of the method gave me the greatest trouble. 

 Higher results were always obtained with thiosulphate than with arsenite 

 or distillation (with H 3 P0 4 ) method. The following table gives the 

 results of some of the analyses : — 





Vol. 



or weight of 



solution. 



Vol. of thio- 

 sulphate with 

 a mixture of 



KI 

 and H3PO4. 



Vol. of thio- 

 sulphate 

 by Penot's 

 method.* 



Remarks. 



I ... 



5 c.c. 



17-66 c.c... 



17-28 c c. ... 



The solution was kept for a few 

 days in diffused light. 



II ... 



10 c.c. 



21-8 c.c. ... 



21-7 c.c. ... 





Ill ... 



10 c.c. 



20 7 c.c. ... 



20-4 c.c. ... 





IV ... 



10 gms. ... 



26-6 c.c. ... 



26-45 c.c. ... 





V ... 



10 c.c. 



19 8 c.c. ... 



19-4 c.c. ... 



The solution was kept for a month 

 in the dark. 



VI ... 



10 c.c. 



109 c.c. ... 



108-4 c.c. ... 



A strong solution kept for five 

 days in the dark. 



VII ... 



10 c.c. ... 



17-1 c.c. ... 



17-1 c.c. ... 



Freshly prepared solution of hy- 

 pochlorite which contained only 

 a trace of chlorate. 



Hypochlorites in presence of chlorates, best estimated by Penot's method. 

 The method then can give approximate but not accurate results. 

 Iodine separates out from an acid solution of potassium iodide in pre- 

 sence of a chlorate, the quantity increasing with duration of contact, 

 temperature, amount of free acid and of chlorate, and other circum- 

 stances. The conditions are rather too numerous to be maintained 

 unchanged during the course of several analyses. In fact, at the boiling 

 temperature in a sealed tube, the decomposition is complete, and chlo- 

 rates may be estimated from the free iodine, a blank experiment being 

 made for the iodine separated owing to the action of the acid on potas- 



* The volume of thiosulphate is calculated from its determined relation with 

 arsenite. 



J. 11. 10 



