364 Dr. P rout's Reply to M. Vauquelin, on [Nov. 



erroneous impression. I did not repeat M. Brugnatelli's experi- 

 ments. My experiments were made, and my paper on the 

 subject read at the Royal Society, before I had seen or even 

 heard of M. Brugnatelli's Essay.* Secondly, the erythric acid of 

 M. Brugnatelli differs altogether in its properties from the pur- 

 puric acid — a substance which M. Brugnatelli had ire ver supposed 

 to exist, as any one may convince himself who chooses to consult 

 his observations. What I consider as the erythric acid of 

 M. Brugnatelli may be thus formed : 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. Brugnatelli. These crystals are also 

 formed when purpuric acid or purpurate of ammonia is dissolved 

 in nitric acid, and treated in a similar manner. I am not quite 

 satisfied with respect to their composition, but at present I con- 

 sider them to be a quadruple salt, formed by the union of super- 

 nitrate and superpurpurate of ammonia ; or they may be a simple 

 compound of nitric and purpuric acid. This salt I had very 

 frequently formed, but had not attended much to its properties. 

 I had also recognized the formation of another principle which 

 was probably the same as that described by M. Vauquelin. 

 This latter, however, I had not examined at all. I allow, there- 

 fore, to M. Brugnatelli, and especially to M. Vauquelin, the merit 

 of having discovered and described the principles respectively 

 claimed by them ; reserving only to myself the discovery of 

 purpuric acid— a principle differing distinctly from both the others, 

 the curious and interesting properties of which absorbed my whole 

 attention, and prevented me from extending my researches 

 further at that time. I intended indeed to extend the inves- 

 tigation further at some future time, and have in fact done so ; 

 but not being quite satisfied on some points, I shall not enter 

 upon the subject at present. 



I am sorry M. Vauquelin ha* gone so far as to deny the 

 existence of purpuric acid. To convince him of his error, I 

 thought the shortest way would be to give him an opportunity of 

 seeing the substance and of examining its properties. Accord- 

 ingly I availed myself a few days ago of an opportunity of trans- 

 mitting to him a small quantity of purpuric acid, purpurate of 

 ammonia, and pure lithic acid. 



In conclusion I may remark that I attribute M. Vauquelin's 

 want of success to his operating upon an impure lithic acid. It 

 is difficult to obtain purpuric acid from the lithic acid constitute 



* My paper on purpuric ncid wai rend at the Royal Society, June 11, ISIS. 

 The translation of AI. Hrugnatelli'x paper did not appear in the Phil. Mag. (s*e 

 the number for July, 1818, vol. 52) till the following month, which waj the m<wt>nm, 

 through which 1 became acquainted with M. Brugnalclli'ii observation*. Theoriginal 

 paper, which I have not yet seen, appeared, 1 hrlieve, in the Giornalo d't Fisica. 

 for the months of Jan. Feb. March, and April, preceding. 



