1879.] Downes and Blunt. Oxalates of the Alkalies. 219 



XX. " Note upon the Behaviour of Oxalic Acid and the Oxa- 

 lates of the Alkalies, and of Potassium Iodide, in Sunlight." 

 By Arthur Downes, M.D., and Thomas P. Blunt, M.A. 

 Oxon. Communicated by Professor Huxley, Sec. R.S. 

 Received June 16, 1879. 



In a previous communication* we stated that a decinormal solution 

 of oxalic acid may be entirely destroyed by sunlight, the decompo- 

 sition being due to oxidation. By a comparison, under like conditions, 

 of oxalic acid and neutral potassium oxalate respectively we further 

 concluded, since the last-named salt appeared to remain unchanged 

 while the former was wholly decomposed, that this destruction of 

 oxalic acid by light was due to the oxidation of its hydrogen. 



During the present year, however, we have made a closer and fuller 

 investigation, which shows that the immunity of neutral potassium 

 oxalate is not absolute, and that we must further extend our views as 

 regards the power of light to promote the oxidation of certain of the 

 elements. 



A measured quantity of normal solution of oxalic acid was carefully 

 neutralised with — 



1. Potassium hydrate. 



2. Sodium „ 



3. Ammonium „ 



4. Lithium carbonate. 



The solution was then diluted up to ten times the volume of the 

 normal oxalic acid originally taken, so that in each case the resultant 

 neutral solutions contained the same weight of the oxalic radical, that, 

 namely, which would be found in an equal bulk of decinormal oxalic 

 acid. Selecting sixteen test-tubes of similar size and bore, we divided 

 them into four sets of two pairs each. In each set respectively we 

 placed one of the above-named solutions (each tube receiving 50 grain 

 measures carefully measured by means of a pipette), a corresponding 

 batch being charged in precisely the same way with a freshly prepared 

 decinormal solution of oxalic acid. All were next raised to boiling 

 point, to prevent development of organisms, and plugged with cotton 

 wool. They were then placed on an outside window-sill, one pair of 

 each batch being incased in laminated lead, the other left freely ex- 

 posed to the sun's rays. This was on March 28. On each of the 

 dates given in the subjoined table an insolated and an incased tube of 

 each set were compared by titration in the following manner. By 

 appropriate dilution and measurement exactly a fifth part of the con- 



* " Proc. Roy. Soc," vol. xxviii, p. 204. 



