1896.] 



Hypochlorites to Chlorates. 



67 



gained in this direction by the researches of Lunge and Landolfc (Society 

 of Chemical Industrial, Journal 1885, 722) on the transformation of 

 bleach-liquor into calcium chlorate — a subject vitally connected with 

 the manufacture of potassium chlorate — yet the circumstances under 

 which the change takes place have not been satisfactorily explained. 

 To throw light on them the following investigation has been undertaken. 



The instability of the hypochlorites, &c., and the absence of charac- 

 terestic tests for their presence, render their detection, separation and 

 direct estimation extremely difficult. Hypochlorites and chlorates when 

 present in a mixture had always been indirectly estimated. 



Before the present investigation was undertaken the methods that 

 have been employed were tested as to their correctness. As measurino- 

 of liquids by means of pipettes, even when very carefully graduated 

 is attended with several sources of error, all the test solutions were 

 made by weight. 



Estimation of chlorates. ^ 



Three distinct methods were employed : — 



(i). Reduction of chlorates by zinc copper couple. The solution 

 was filtered, and as the residue invariably contained traces of chloride 

 in the form of insoluble zinc oxychloride, it was acidified with pure 

 dilute nitric acid and thoroughly washed. The precipitated zinc hydrate 

 (there being always free alkali present) was dissolved by the addition 

 of more acid, and then the solution was digested with precipitated 

 calcium carbonate and estimated gravimetrically as silver chloride or 

 volume trically by standard silver nitrate solution. 



(ii). (a) Digestion with stannous chloride in hydrochloric acid 

 solution, and titration of the excess by permanganate. 



(6) Digestion with ferrous sulphate precipitated by alcohol, 

 and titration of the residual iron by bichromate or permanganate. The 

 purity of the ferrous sulphate was tested by igniting the salt in a 

 platinum crucible and weighing as oxide. The results were highly 

 satisfactory. Thus: — 



Weight of Salt. 



Wt. 



of Fcg O3. 



Percentage of Fe 

 as determined. 



Calculated per- 

 centage of Fe. 



1-8710 grams 

 1-7914 „ 

 1-5129 „ 



0-5400 gm. 

 0-5167 „ 

 0-4367 „ 



20-20 

 20-19 

 20-20 



20-15 



The slightly higher result was due to slight efflorescence of the salt. 

 In actual analysis the salt was dissolved in dilute sulphuric acid, the 



