76 



Mr. E. Scliimck on the Colouring and 



[Reeess_, 



ever, no one has obtained any substance from urine having exactly the 

 same properties. The urines which deposit the blue colouring-matter are 

 not found to exhibit any peculiarities in other respects, nor does the deposit 

 appear to be characteristic of any peculiar class of diseases. It seems 

 occasionally even to make its appearance during a state of perfect health. 

 Sometimes the deposit seems to contain also another colouring-matter, 

 more easily soluble in alcohol and ether, to which it communicates a fine 

 purple colour. 



The deposits of urate of ammonia and urate of soda, which are formed 

 in urine during fever and other diseases, are always found to exhibit 

 different shades of red, varying from pink to carmine. To what this 

 colour is to be attributed has not yet been satisfactorily ascertained. 

 Proust*, who was the first chemist to examine these deposits, thought 

 that he had discovered in them a peculiar coloured acid, which he called 

 7'osacic acid. It is almost certain, however, that the acid properties of 

 this body were due to an admixture of uric acid. Indeed, Vauqueiin, after 

 an examination of this so-called acid, arrived at the conclusion that it was 

 a compound of ordinary uric acid with an intensely red colouring-matter. 

 Vogel f , it is true, professed to have obtained pure rosacic acid by treating 

 the crude deposits with boiling alcohol, but as, according to him, it is con- 

 verted with great facility into uric acid by the action of sulphuric and 

 nitric acid, it is very probable that his substance still contained some of 

 the latter acid, and that the supposed conversion consisted merely in a 

 destruction of the organic colouring- matter. Fromherz and GugertJ also 

 made some experiments with these red deposits, from which they infer 

 that rosacic acid consists of a neutral, red extractive colouring-m.atter, 

 mixed with uric acid and urate of soda, which may be separated by treat- 

 ing the mixture first with water and then with warm alcohol, which dis- 

 solves the colouring-matter. The latter, after being thus separated from 

 the other constituents, no longer yields uric acid. Prout § suggested that 

 the colour of the red deposits might be due to purpurate of ammonia, the 

 purpuric acid being formed in some unexplained manner by the action of 

 nitric acid on a portion of the uric acid contained in them. To this it 

 was objected by Berzelius H that purpurate of ammonia is insoluble in 

 alcohol. He mixed urate of ammonia with a solution of a purpurate in 

 acetic acid, which does not destroy the colour, and he observed that the 

 precipitated uric acid acquired a pale pink colour closely resembling that 

 of the urinary deposits ; but this colour was not removed by boiling alcohol, 

 in which, on the contrar}^, the colouring-matter of the red deposits is easily 

 soluble. Buvernoy % asserts that he succeeded in preparing a colouring- 

 matter identical with that of the red deposits by evaporating ordinary 



* Annales ds Chimie, t. xxxvi, p. 265. t Ibid. t. xovi. p. 306. 



\ Schweigger's Journal, B. I, S. 199. § Annals of Philosophy, vol. xv, p. 155. 



II Lelirbuch der Chcmie, B. ix. S. 421. 



5i Untersuchungen iiber den menschlichen Uriu. Stuttgart, 1835. 



