292 BACON. 



attempt to confirm these results under the influence of the tropical sunlight. The 

 experiment was performed under varying conditions, in open flasks and in sealed 

 tubes, and with the acetate, sulphate and nitrate of uranium, but the results in 

 every case were negative. No formaldehyde and no hydrogen peroxide could be 

 detected. In the course of this work it was found that glyoxalic acid (phenyl 

 hydrazone melting at 121°) is one of the products formed in the decomposition of 

 acetic acid and uranyl salts in the sunlight. * 



I was not able to substantiate the fact stated in the older literature 10 

 that large amounts of formic acid are formed in the reaction of uranyl 

 salts on oxalic acid solutions, as is shown by the following typical 

 experiment: 



Twenty-five cubic centimeters of 10 per cent oxalic acid to which 25 cubic 

 centimeters of 5 per cent uranyl sulphate solution had been added, were exposed 

 to the sunlight for several days until the reaction was apparently complete. 

 The solution was diluted to a volume of 100 cubic centimeters and 75 cubic centi- 



N 

 meters distilled. This distillate was titrated with — sodium hydroxide, using 



nhenolphthalein as an indicator, and gave less than 0.002 gram of acid, calculated 

 as formic. Titration of the distillation residue proved that oxalic acid had in 

 all instances been completely decomposed. Therefore, it is evident that when the 

 reaction of uranyl salts and oxalic acid goes to completion, there is practically 

 no formic acid left in the solution. In my former paper 20 I found that formic 

 acid was not readily decomposed by uranium salts, hence it appears probable that 

 very little was formed during the reaction. However, I will take up this phase 

 of the question at a later date. 



Duclaux 21 made very extensive studies on the actinic power of the 



N 

 sun, using a - solution of oxalic acid exposed in flat, shallow vessels. 



I shall discuss his results at some length, because, while I do not con- 

 sider his solution of great value as a chemical photometer, still his work 

 is given in such form that comparative measurements under the same 

 conditions could be carried on in Manila. This author states : 



"The chemical radiations of the sun reaching the limits of our atmosphere 

 become modified while passing through it, according to a law which is peculiar 

 to them, and, so far as can be seen in so new a subject, their absorption is not 

 the same as that of the calorific or luminous parts of the spectrum." After 

 speaking of the fact that landscape photographers often encounter days, on which, 

 while the sun is apparently as bright as usual, it is difficult to obtain pictures 

 with normal exposures, he continues, "There are daj's on which for some unknown 

 reason, the chemical impression is much slower than on others" and "The very 

 fine day of September 15, 1888, gave a combustion of only 9 per cent when the 

 slightly veiled day of September 28th gave a combustion of 49 per cent." Thus 



10 hoc. cit. 

 -" Lac. cit. 

 21 hoc. cit. 



