1820.] Physical Science during the Year 1819. 23 



When pure uric acid is treated with nitric acid till the pink 

 colour appears, Dr. Prout showed that a peculiar acid is formed, 

 to which he gave the name of purpuric acid, and the peculiar 



Jjroperties of which were described in the historical sketch of 

 ast year. 



It would appear from some notices published in the periodical 

 publications, that Vauquelin has attempted without success to 

 prepare purpuric acid. It is difficult to say to what cause the 

 want of success of this very laborious and dexterous chemist is 

 to be ascribed ; but as I have myself had an opportunity of 

 seeing purpuric acid, and even of examining its properties, it is 

 not possible for me to entertain the least doubts about the reality 

 of its existence. 



5. Ferrochi/azic Acid. — I have satisfied myself by the experi- 

 ments to be stated in a future number of the Amuih of Philo- 

 sophi/, that the constituents of ferrochyazic acid are the fol- 

 lowing : 



2 atoms carbon = 1-500 



1 atom hydrogen = 0'125 



1 atom azote = 1-750 



i atom iron = 1*750 



5-125 



so that it is a compound of five atoms (supposing the iron to be 

 in reality one atom), and the equivalent number for it is 5-125. 

 I have had the curiosity to analyze several of the ferrochyazates, 

 and have had the satisfaction to find that the composition of all 

 of them agrees very well with this equivalent number for the 

 acid. 



6. Succinic Acid. — A singular process of Dr. John by which 

 he obtained succinic acid, is given in the Annah of Philosophj/, 

 XV. 388. I have not tried the experiment, and cannot pretend 

 to form any opinion respecting it. 



7. Pyronialic Acid. — It was observed by Vauquelin and by 

 Braconnot, that when sorbic acid is distilled in a retort, it sub- 

 limes in part in white needles, and partly passes over into the 

 receiver in the state of a liquid. When this liquid is evaporated, 

 it yields acid crystals, differing in their properties from the acid 

 from which they were produced. M. Lassaigne has examined 

 the properties of this new acid, and has given it the name of 

 pijromatic acid, in consequence of Braconnot's discovery of the 

 identity oi sorhic and /««//c acids. 



These crystals are not altered by exposure to the air. They 

 melt, when heated to the temperature of 117-5°, and, on cooling, 

 assume the appearance of a pearl-coloured mass crystallized in 

 diverging needles. When thrown upon red-hot coals, they fly 

 off in an acid smoke, which excites cou<>hin<i\ without leaving 



•111 ~0' c? 



any residue behnid. When distilled in close vessels, the great- 



