OXALIC ACID AND URANIUM SALTS AS A PHOTOMETER. 299 



• . N 



In another experiment 100 cubic centimeters — oxalic acid were taken and 



10 cubic centimeters pipetted out each day and titrated. 



late, 1898. 



Days. 



Titre. 



June 29 







11.00 



July 3 



4 



10.39 



July 9 



10 



9.40 



July 17 



18 



7.42 



July 25 



20 



5.25 



July 31 



32 



3.52 



Enough data have been given to show that the decomposition of oxalic acid 

 proceeds much more rapidly in Manila than in those places in the temperate zone, 

 where it has been measured. 



The effect of various other salts on the decomposition of oxalic acid 

 was also studied, the results follow. January 19, 1910." Bright sun 

 from 9 to 10 a. m. Bather cloudy after 10 a. m. All flasks exposed 

 from 9 a. m. to 1 p. m. 



Number. 



10 per 

 cent 



oxalic 

 acid. 



Cubic centimeters of other salts. 



Decom- 

 position. 



1 _ 



cc. 

 5 

 5 



5 

 5 

 10 

 10 

 10 

 10 

 10 

 10 





Per cent. 1 

 40 

 60 

 66 

 15 







8 



7 



5 



5 

 10 



2 ___ ___ 



5, 1 per cent ferrous sulphate FeS0 4 



5, 1 per cent ferric chloride FeCl 3 



10, 1 per cent sulphuric acid _ _ 



3 __ _ 



4 



5 _ .. 



Trace, copper sulphate - . 



6 _ _ ___ H 



7 _ .'_ 



Trace, manganese sulphate 



Trace, mercuric chloride ._ 



8__ :___ 



9 _ 



10 











It is evident that many other "salts accelerate the decomposition of 

 oxalic acid, just as do those of uranium. 



A statement exists in the photochemical literature 2 " that platinum, 

 gold and iridium salt solutions are reduced more easily hj oxalic acid 

 which has been exposed to the sun, than by solutions which have not 

 been insolated. 



In view of the facts already presented as to the formation of hydrogen 

 peroxide by the insolation of oxalic acid solutions, this is easily under- 

 stood. 



The older literature contains several statements to the effect that Eder's 

 solutions are subject to a marked period of induction, although a careful reading 



29 Ann. d. Chem. (liebig) (1862), 122, 193. Draper, Phil. Mag. (1857), 14, 

 101, used the separated gold as a measure of the sunlight's action. 



