Chemical Science. 373 



refuses to crystallize. An effect which may be ascribed to the 

 flocculent matter remaining dissolved with it. 



They account for the blue tint produced by ferro-prussiate 

 of potash in muriatic acid that has been boiled on uric acid, 

 which colouring has been ascribed to many other causes than 

 the true one. 



Finally, admitting, with M. Vogel, that the rosacic acid is 

 converted into uric acid by the solvent powers of various acids, 

 we shall perceive in this an effect similar to the preceding ; and, 

 if we suppose the coloured and flocculent substances to vary in 

 quantity, as in the intermitting and inflammatory fevers which 

 produce rosacic acid, the colour and the constitution of the 

 urine will, of course, vary also. In the same way, therefore, 

 as variations in the proportions and qualities of extraneous 

 substances render uric acid calculi of a yellow colour more or 

 less deep, or sometimes even red, it will be fair to suppose 

 that the rosacic acid is a combination of animal substances, of 

 which uric acid is the base. — Giornale di Fisica, 1. p. 132. 



6. Purpuric Acid. — Dr. Prout, in answer to what has been 

 said by M. Vauquelin, denying the existence of purpuric acid, 

 has published a brief reply, which carries with it the tone of 

 perfect security ; and there is not, perhaps, much doubt that M. 

 Vauquelin will ultimately prove to be wrong. Dr. Prout denies 

 being a repeater of M. Brugnatelli's experiments, and avows his 

 opinion that the erithric acid of M. Brugnatelli is very different 

 to purpuric acid. Dr. Prout directs the formation of erithric 

 acid thus: dissolve pure lithic acid in a slight excess of nitric 

 acid, evaporate the solution slowly, and put it by to crystallize 

 in a warm place: transparent colourless crystals will be speedily 

 formed, having all the properties ascribed to them by M. Brug- 

 natelli. These crystals are also formed when purpuric acid, or 

 purpurate of ammonia, is dissolved in nitric acid, and treated 

 similarly. Dr. Prout is not decided with respect to their com- 

 position, but thinks they are either a compound of super-nitrate 

 and stiper-purpurate of ammonia, or a simple compound of nitric 

 and purpuric acid. 



