294 Reply to Mr. Hume's Answer [April, 



tallization ;" if this is the case, the acids he employed were con- 

 centrated acids. With this view of the subject, let us turn to Mr. 

 Hume's paper in the Phil. Mag. for 1802, in which his fourth and 

 sixth discoveries are thus described : " carbonate of barytes may 

 be entirely changed into nitrate by nitrous acid in its con- 

 centrated stste." — " Carbonates of barytes may be rendered 

 int.; muriate bv concentrated muriatic acid." Mr. Hume fur- 

 ther contends, that there is no ground for asserting, that suf- 

 fering the muriatic and nitric acids to form their respective salts 

 from the decomposition of the carbonate " is precisely the same as 

 adding their salts, or more particularly their solutions, to the re- 

 spective acids ;" he does not, however, attempt to show the differ- 

 ence ; the facts of the case are, I assert, simply these : when 

 crystals are added to the acid they remain undissolved; when a 

 solution is substituted for tiiem, it is decomposed, and crystals are 

 deposited on account of their insolubility; and when water has been 

 put to a strong acid, carbonate of barytes is decomposed, an aqueous 

 solution is first formed in, and then decomposed by, the acid; 

 crystals are formed, and remain undissolved ; the manipulation in 

 these cases differs, but the same substances are employed, and the 

 same results produced ; and these in eveiy case (again to copy Mr. 

 H.'s words) may be correctly described by stating " that such is the 

 avidity of nitrous and muriatic acids for water, that they will attract 

 even the whole of the water of solution from their respective salts." 



Mr. Hume now says that when he published his paper on barytes 

 in 1802, " it had been a common practice to ascertain the purity 

 of nitrous acid, and even to purify it, by dropping into it a solution 

 of nhrate of barytes." This statement, as well as some other parts 

 of Mr. Hume's letter to you, Sir, would induce any one, unac- 

 quainted with his controversial style, to suppose that his alleged 

 discoveries were attended with directions for avoiding so erroneous 

 a practice. This, however, is entirely an after-thought ; for the 

 fact is, that Mr. Hume's paper on barytes does not contain any 

 notice of the errors which the facts he mentions are likely to occa- 

 sion ; and consequently no "instructions" whatever are offered on 

 the subject of purifying nitric acid. The experiments are related 

 both by Mr. Hume, and by Sage who preceded him, without any 

 reference to this subject ; and nothing can be learned from the 

 former which the latter does not supply. 



According to the purpose to be answered Mr. Hume puts differ- 

 ent constructions upon similar phrases. Thus, in the paper on 

 barytes, the quotation " Tous les acides niineraux decomposent ce 

 sel," meaning " carbonate de baryte," must be translated diluted 

 amh; otherwise he must abandon a claim already quoted, but not 

 very clearly made out, to the discovery that carbonate of barytes is 

 decomposable by concentrated nitric and muriatic acids : whereas, 

 in his letter, he attempts to show that Lagrange was ignorant that 

 strong nitric acid decomposes solution of nitrate of barytes ; and to 

 prove this case, the words " acide nitrique," vviiich he quotes from 

 this author, must be rendered concentrated nitric acid. Thus Mr. 



