284 BACON. 



for believing the tropical sunlight to contain a large proportion of 

 such rays, therefore it was considered desirable to use a solution sensitive 

 to such short wave lengths in the first series of measurements of the 

 chemical effects of tropical sunlight. I do not consider that there is 

 any good reason for classifying the sun's rays into infra-red or heat 

 rays, visible rays, and ultra-violet or chemical rays, as there are just as 

 many chemical reactions affected by light corresponding to the visible 

 and even infra-red parts of the spectrum as there are by the ultra-violet 

 portion. 



Since the time of Seekamp 14 many papers have been published on * 

 the subject of the decomposition of oxalic acid, but it is rather remark- 

 able that none of the investigators have followed the reaction quanti- 

 tatively, in order to study the effects of concentration,, various catalyzers, 

 etc., upon its rate. For practical purposes, the decomposition of oxalic 

 acid under the influence of uranyl salts may be assumed to take place, 

 as follows; H 2 C 2 4 -^C0 2 +C0+H,0. The amount of formic, acid pro- 

 duced is small, and the quantity of uranyl salt reduced during the 

 •initial stages of the reaction is also negligible, so that for comparative 

 measurements these factors may be disregarded. 



In my earlier work on this subject I used the gas given off as a 

 measure of the amount of decomposition of the oxalic acid. However, 

 it is well known that reactions measured by gas evolution are subject 

 to errors, due to the size, shape, and material of the vessel, and the 

 possibility of supersaturation of carbon dioxide solutions. Hence, in 

 my later work, I always determined the undecomposed oxalic acid, 

 acidified Math sulphuric acid, by direct titration with potassium per- 

 manganate, after removal of the uranium salts with a- slight excess of 

 ammonium hydroxide. The uranyl salt-oxalic acid solutions were ex- 

 posed to sunlight in 100 cubic centimeter Erlenmeyer flasks and the 

 rate of decomposition determined by direct titration. 



In the first series of measurements the quantities of oxalic acid and 

 uranyl salt were varied within rather wide limits to discover the effect 



"Arm. Chem. (Liebig) (1862), 122, 113; Ibid. (1865), 133, 253. Fay, 

 Amer. Chem. Journ. (1896), 18, 269, gives a good summary of the older work on 

 this subject. See also Baur, Ztschr. f. phys. Chem. (1908), 13, 305; Luther, 

 Ztschr. f. anorg. Chem. (1907), 54, 1. 



