THE TROPICAL SUNLIGHT. 9 



Comparisons made in August between St. Pierre le Port, on the Channel, and 

 Helsingfors (latitude 60° 10') gave as a maximum 44 per cent of decomposition 

 in France and 77 per cent in Finland, between the hours of 8 and 4, a most 

 remarkable result, tending to show that the chemical effect of the sun's rays, in 

 late summer, is greater at the far northern latitude of Hesingfors than in France. 

 In Algeria, during the same months, the maximum was only 14 per cent. Accord- 

 ing to Duclaux's experiments, therefore, the chemical effects of the sun's light 

 diminishes in the summer months as we proceed from a northern climate toward 

 the equator. 



The above results do not hold good in Manila. Here, following the 



method of Duclaux, Doctor Bacon has found that, using 10 cubic centi- 



N 

 meters of rj. oxalic acid, the decomposition of oxalic acid, between the 



hours of 8 and 4, is almost always practically complete. Thus, the figures 

 for four days are 68, 96, 85, and 10.0 per cent, respectively, and even on 

 a day over one-half of which was cloudy (January 19), complete oxidation 

 had taken place by 5 o'clock in the afternoon. While there is no doubt as 

 to the results obtained by Duclaux in the dry climate of Algeria, near a 

 great desert, it certainly is true that those reached in Manila are contra- 

 dictory to the ones which have been quoted, and that there is here a marked 

 increase in the rate of decomposition. 



However, the oxidation of oxalic acid in the sunlight suffers from a 

 great defect. Duclaux noticed that a solution when first exposed decom- 

 posed very slowly and that the reaction is subsequently rapidly acceler- 

 ated. We have shown here that this phenomenon depends on the forma- 

 tion of hydrogen peroxide, and that the increasing rate is due to 

 autocatalysis. While the method, therefore, gives a certain measure of 

 comjjarison, it is not above criticism. 



The decomposition of oxalic acid in the presence of uranium acetate is 

 not dependent upon oxidation, and is not accelerated by autocatalysis, and 

 is therefore much better adapted to comparative study. 15 Doctor Bacon 

 also had the good fortune, while in America on leave, to compare this 

 reaction in Chicago with that in Manila. The time in Chicago was 

 during the months of May and June ; the total average extending over ten 

 days gave, for Chicago, approximately 100 cubic centimeters of gas in 

 two hundred minutes, and in Manila, with the same solutions, 100 cubic 

 centimeters in forty minutes. It is also at present noticeable, in this 

 climate, that as the altitude of the sun is increasing, the decomposition is 

 accelerated; thus, January, 1910, gave an average decomposition of 0.081 

 gram of oxalic acid per hour as compared with 0.090 in the middle of 

 February. The optimum day in Manila has far exceeded the ratio of 

 5 to 1 observed above, and has more nearly reached 20 to 1. 



ls Raymond F. Bacon. This Journal, Sec. A (1907), 2, 129. 



