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



carbon dioxide are formed as the result of the interaction of hydrogen peroxide 

 and formaldehyde is a piece of evidence which strongly supports the view- 

 that the latter substance is formed in the experiments we are considering, 

 provided that formic acid does not give rise to these gases under similar 

 conditions. As no record of experiments on these Hues could be found 

 the point was investigated. The mixture of formic acid and hydrogen or 

 uranium peroxide was placed in a Zeisel flask with a condenser attached. 

 This was first connected with some bulbs containing lime-water, and a 

 current of C0 2 -free air was passed through the apparatus while the mixture 

 was heated on a water-bath. Considerable quantities of carbon dioxide were 

 evolved, as shown by the precipitation of calcium carbonate. A fresh 

 quantity of the reaction-mixture was then taken, and the apparatus con- 

 nected with a Schiff's nitrometer while a current of carbon dioxide was 

 passed. Not a trace of hydrogen was evolved, although the mixture was 

 boiled for three hours. There is apparently no difference between the 

 reactions in the case of hydrogen peroxide and uranium peroxide, except 

 that the latter proceeds more slowly. These experiments were carried out 

 in the dark. 



Experiments with ordinary uranic oxide showed that formaldehyde reduced 

 it both in the dark and in the light, uranous oxide and a formate being- 

 produced, but only in the light was the violet colour observed. It appears 

 that this coloration is merely a surface effect, since the precipitate, when 

 dissolved in acid and reprecipitated, has the ordinary black colour of uranous 

 oxide. 



The following experiments bring out rather more clearly the distinction 

 between formic acid and aldehyde mentioned above : — 



To one of two tubes containing pure uranium peroxide, a dilute solution 

 of formaldehyde was added ; to the other, some dilute formic acid. After 

 exposure to light from February 16 to February 19, no effect was visible in 

 the tube which contained formic acid, whereas the other contained uranous 

 formate and a violet-coloured precipitate. In order to examine the gases 

 produced in the two cases, two more tubes were prepared, one of which 

 (a) contained uranium peroxide, formic acid, and formaldehyde, while the 

 other (b) contained uranium peroxide and formic acid only. Both were 

 drawn out to a capillary, exhausted, and sealed. They were exposed to light 

 from February 27 till March 6, when the gases were pumped out and 

 examined : (a) contained 4'8 c.c. of carbon dioxide and 4*8 c.c. of hydrogen, 

 while (6) contained 9 - 8 c.c. of carbon dioxide and no hydrogen. 



There is thus no direct experimental evidence that formaldehyde is 

 produced under these conditions, that is to say, it has not been isolated and 



