370 



Messrs. F. L. Usher and J. H. Priestley. [Dec. 16, 



solution of uranium acetate exposed to sunlight in a glass apparatus, a pre- 

 cipitate consisting of a mixture of uranium peroxide with lower oxides was 

 formed, and that the solution contained formaldehyde. Bach regarded the 

 uranium acetate solution as playing the part of a chemical and an optical 

 sensitiser, and considered the decomposition of the carbon dioxide to result 

 primarily in the production of hydrogen peroxide and formaldehyde. 



Decomposition of Carbon Dioxide Outside the Plant. — The experiments of 

 Bach have been repeated and confirmed, both as to the production of peroxide 

 and formaldehyde. 



The amount of decomposition obtained in three weeks in bright weather 

 was extremely small, and this appears to us to be explained by the fact that 

 (1) as a chemical sensitiser uranium acetate is far inferior to that which exists 

 in a green plant, inasmuch as the separated oxygen (in whatever form it may 

 exist) is not entirely removed from the sphere of action, as in the case of 

 the plant, but remains as a fairly insoluble peroxide which undergoes a rever- 

 sible change with the other product, namely, formaldehyde ; (2) as an optical 

 sensitiser uranium acetate is inferior to chlorophyll to the extent that it 

 possesses no absorption at all in the red, and only two faint bands between 

 F and G. 



In view of the extreme slowness of the reaction under these conditions, 

 experiments were made with very large concentrations of carbon dioxide- 

 Tubes of Jena glass, 40 cm. long and 8 to 10 mm. bore, were about three- 

 quarters filled with 1"5 per cent, uranium acetate solution, and cooled in liquid 

 air while some carbon dioxide was passed in. They were then sealed, and 

 suspended outside a south window in bright sunshine. "Within 15 minutes of 

 warming up to the air temperature, a precipitate began to form, and in 

 24 hours the reaction was complete. The tubes when opened were found to 

 contain uranium peroxide and formic acid, but no formaldehyde. The formic 

 acid was obtained by distillation of the filtrate from the peroxide, and was 

 characterised by (1) reduction of silver nitrate, (2) reduction of Fehling's 

 solution, and (3) properties of lead salt. 



Thus with very large concentrations of carbon dioxide, formic acid, and not- 

 formaldehyde, results. 



These experiments are open to the objection that since uranium acetate is 

 to a considerable extent hydrolysed in solution, the formaldehyde in one case 

 and the formic acid in the other may possibly have been derived from the 

 acetic acid present. 



It has been found that uranium sulphate in a 2-per-cent. solution functions 

 in the same way as the acetate. An experiment with the sulphate, conducted 

 in the usual way, i.e., bubbling carbon dioxide through the solution, which 



