1820.] Physical Science during the Year 1819. 25 



still sensibly bitter. The acid was purified by repeated solutions 

 in water and alcohol till it had lost its bitter taste. Thus puri- 

 fied, it possessed the fi^Uowing characters : 



(1.) it does not precipitate lime-water. 



(2.) With barytes it forms a somewhat soluble salt. 



(3.) It precipitates nitrate of barytes grey. 



nitrate of silver, deep-yellow. 



muriate of tin, yellow. 



muriate of gold, reddish-brown, 



(4.) It does not act upon the solution of protosulphate of iron, 

 but, when dropped into the persulphate, it occasions a copious 

 green precipitate, of a very dark colour. 



(5.) It forms an abundant precipitate when dropped into the 

 solution of sulphate of magnesia. 



(6.) When treated with nitric acid, it is not converted into 

 oxalic acid. (Jour, de Pharm. v. 6.) 



9. Pi/ro-uric Acid. — This substance in a state of impurity was 

 first noticed by Scheele. It was afterwards more particularly 

 examined by Dr. Henry. MM. Chevallier and Lassaigne have 

 lately procured it in a state of purity, and determined its proper- 

 ties and its composition. 



When uric acid, or calculi, consisting chiefly of that substance 

 are distilled in a retort, a sublimate arises in silvery white plates. 

 This substance has been long known under the nam'e of Scheele's 

 sublimate. Chevallier and Lassaigne have ascertained it to be 

 a pyro-urate of ammonia. They dissolved it in water, and preci- 

 pitated the acid by means of subtritacetate of lead. The white 

 precipitate, after being washed with water, was decomposed by 

 means of sulphuretted hydrogen gas. The hquid being now 

 evaporated yielded pure pyro-uric acid crystallized in small white 

 needles. Its characters are as follows : 



W'hen heated, it melts, and sublimes entirely in white needles. 

 When passed through a red-hot glass tube, it is decomposed into 

 charcoal, oil, carburetted hydrogen, and carbonate of ammonia. 

 Cold water dissolves about'the fourth part of its weight of it. 

 The aqueous solution reddens vegetable blues. It dissolves in 

 boiling alcohol, and as the solution cools, precipitates again in 

 small white grains. It dissolves in concentrated nitric acid. By 

 evaporation to dryness, it is obtained without any alteration. 

 This shows that pyro-uric acid differs from uric acid, which, by 

 that process, is converted into purpurate of ammonia. 



Lime combines with this acid, and forms a salt, which crystal- 

 lizes in stalactites, and which has a bitter and slightly acrid 

 taste. When slightly heated, it melts, and assumes on coohng 

 the consistence of yellow wax. It is composed of 



Acid 91-4 38-526 



Lime 8-6 3-625 



lOO-O 



