Chemical Science. 159 



The chloride of silver being separated, I obtained a fine red 

 fluid, in which there was neither silver nor hydro-chloric acid. 

 The following are the properties of this colouring matter ; it is 

 neither acid nor alkaline ; acids destroy its colour, making 

 it yellow, and nothing can restore its first tint. If only a small 

 quantity of acid is added, the colour passes to scarlet before it 

 disappears. The alkalies, and the oxides of lead, silver, and cop- 

 per, convert it to a violet colour, but do not destroy it. Lime 

 does not act strongly on its colour ; its combination with it pre- 

 serves the red tint. It adheres to metallic oxides, neutral salts, 

 and to animal and vegetable substances; but it cannot long 

 resist the action of air and the sun, which change it to 

 yellow. 



It follows from what I have detailed, that by the action of 

 nitric acid, chlorine, and iodine, on uric acid, there is formed 

 a peculiar acid, which is without colour, and an azotatcd co- 

 louring matter, which is not acid, but which has a stronger 

 analogy to the bodies of this class than to the alkalies. It is 

 this colouring matter, which, mixed vrith the peculiar acid of 

 the calculus, has made Messrs. Brugnatelli and Prout believe 

 the acid itself was coloured, and has caused one to give it the 

 nanie of erythric acid, and the other purpuric acid ; names, 

 which we may observe, are not applicable to it. 



I have made a great number of experiments on this acid, 

 and its combinations with different bodies ; I have also sub- 

 mitted the colouring matter to many tests, of which some 

 have given me curious results. I have carefully examined the 

 manner in which nitric acid, chlorine, and iodine, act on uric 

 acid, and the various bodies which, according to circumstances, 

 result. That which required the most time was a search after 

 some simple and exact method of separating the acid and 

 colouring matter from each other. I shall shortly publish these 

 experiments, with the necessary details. 



As names are required for these two substances, I shall pro- 

 pose, for the present, for the acid, the name of peroxygenated 

 uric acid*, and for the colouring matter, that of erythrine. 



* Better oxy-uric acid. 



