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Messrs. F. L. Usher and J. H. Priestley. [Apr. 30, 



bonate. In this case the whole of the bicarbonate was converted into 

 formate. When neutral or slightly acid gelatine was used, no formic acid 

 could be detected. With very large concentrations of carbon dioxide, formic 

 acid appears to be the sole product, since when sealed tubes containing 

 chlorophyll, water, and liquid carbon dioxide were exposed to light, no 

 formaldehyde was found, though a considerable quantity of formic acid was 

 produced. 



If, however, formic acid is an intermediate product in the photolysis of 

 carbon dioxide in the plant, the latter should be able to build up carbohydrates 

 from this substance. This was found to be the case with Modea, which, when 

 exposed to light in a 0'02-per-cent. solution of formic acid, gave off oxygen 

 and formed starch ; no starch was formed, or oxygen evolved, from Modea 

 kept in the dark, carbon dioxide being carefully excluded in each case. When 

 the plant was previously killed, the same changes took place as when carbon 

 dioxide was used, that is to say, the chlorophyll became bleached, and the 

 plant was subsequently found to contain formaldehyde. 



II. The Photolytic Decomposition of Carbon Dioxide in the Presence of 

 Uranium Compounds. 



In a previous paper, to which reference has been made above, it was stated 

 that Bach's observations had been repeated and confirmed in the case of 

 uranium acetate, minute quantities of formaldehyde being found in the 

 distillate. Since then our attention has been called to a recent paper by 

 Euler,* who was unable to confirm Bach's observations. A more detailed 

 investigation has therefore been made, and, since it cannot be proved that 

 any particular organic substance which may be produced is formed from the 

 carbon dioxide, and not from the electro-negative portion of the organic salt 

 when the latter is employed, a purely inorganic sensitiser has been used in 

 the present series of experiments. 



In the first of these, which was a repetition on a larger scale of one which 

 has already been described, a large Pettenkofer tube was filled with a litre of 

 2-per-cent. uranium sulphate solution, and a slow current of carbon dioxide 

 was passed through it, the whole apparatus being placed on the roof in order 

 to utilise all the available sunlight. Within an hour of passing the carbon 

 dioxide the contents of the tube were considerably turbid, and at the end of 

 the exposure, which lasted from January 27 till February 9, the precipitate 

 amounted to several grammes, and was of a pale violet colour. The greater 

 part was soluble in acetic acid, and was found to be a mixture of uranous 



* ' Ber. deut. chem. Ges.,' 1904, vol. 37, p. 3415. 



