220 Downes and Blunt. On Potassium Iodide. [June 19, 



tents of each tube was taken, treated with an excess of sulphuric acid y 

 and a standardised solution of potassium permanganate run in until a 

 faint permanent pink tinge remained in the solution when warmed. A 

 direct measure, inversely as the quantity of permanganate required,, 

 was thus obtained of previous oxidation. 



Experiment started March 28. 



Potassium permanganate solution required for oxidation.* 





April 25th. 



June 9 th. 



Incased. 



Insolated. 



Incased. 



Insolated. 





7-5 c.c. 



2-0 c.c. 



7-25 c.c. 



c.c. 







7-5 „ 



51 „ 



73 „ 



2-2 „ 







7-4 „ 



6 05 „ 



7-2 „ 



5-2 „ 







7-5 „ 



6-1 „ 



71 „ 



5-4 „ 







7'3 „ 



62 „ 



7-25 „ 



6-0 „ 





Freshly prepared decinormal 



| 7-3 



c.c. 



7-2 



c.c. 



Our previous statement as to the total oxidation of oxalic acid in 

 sunlight is thus confirmed, but we learn for the first time that in no 

 case does an oxalate of an alkali entirely escape the oxidising action of 

 sunlight, although whether the various alkali salts always obey the 

 relative proportions of the table above given is a question on which 

 at present we express no opinion whatever. It is, however, an in- 

 teresting question which constituent of their molecules is the subject 

 of oxidation. Hydrogen, except in the case of the ammonium salt,f 

 is out of question. The uniformity of the initial action indicated 

 the possibility of an oxidation of carbon, but a collateral study of the 



* Disregarding the trifling differences in the decimals as due to unavoidable error 

 the incased liquids remain practically unchanged. From other experiments, not 

 here given, however, it would appear that to obtain this stability the solutions must 

 be boiled, probably on account of the tendency to development of low organisms in 

 the dark. 



f Speculation as to the cause of the greater oxidation of this compound, as com- 

 pared with the other alkali-oxalates in the above experiment, would be premature ; 

 and, although the suggestion that a portion of the hydrogen of the JN"H 4 is seized 

 upon, offers itself, it is only right to say that the possibility of other explanation has 

 presented itself to us. This we leave for the present. 



We may remark incidentally, that a mixture of gaseous ammonia (NH 3 ) and 

 oxygen in a glass tube over mercury, underwent no change in volume after months 

 of insolation last year. 



