Reply to a Review in Brande's Joimml of Science. 125 



paved is of a turbid yellowish colour, instead of being colourless 

 and transparent, and that it deposits a considerabie sediment ; 

 both which circumstances seern greatly to militate against its 

 purity." 



The second charge against the reviewer, or that of ignorance 

 of the subject on which he has undertaken to pronounce, is thus 

 substantiated, 1. The reviewer states at page 400, that he is 

 " not quite clear" whether Gay Lussac gave the name of cyano- 

 gene to the base of hydrocyanic acid " because it burns with a 

 hlueish purple flame, or because it is essential to the production 

 of Prussian blue ;" whereas, Gay Lussac is positive as to the 

 latter reason ; and every chemist aco^uainted with the subject 

 knows it to be so. — 2. The reviewer asserts, that the acid ob- 

 tained by Scheele's method, " is of variable composition, be- 

 cause Prussian blue is not always of equable purity:" but this is 

 not true in practice. Mr. Garden has prepared prussic acid ac- 

 cording to this method for the last three years and a half, with 

 an invariable precision of result and equality of strength, which, 

 to judge of its constant specific gravity, is stronger than that pre- 

 pared at Apothecaries' Hall. — 3. The reviewer has acknowledged 

 his inability of obtaining pare prussic acid by Vauquelin's method, 

 which, he asserts to have tx\e^ frequently. But the want of suc- 

 cess in his case must be ascribed to his ignorance in chemical 

 manipulations, as you well know ; for you have seen pure prus- 

 sic acid prepared according to that method. — 4. The reviewer 

 says he camiot understand the following passage of my work, 

 containing the well known hydrodynamic axiom, that " the 

 weight of fluids is equal to their volumes multiplied by their den- 

 sities." I can only observe, in reply, that if he is a stranger to 

 mathematical language, he has only to refer to Dr. Young's lec- 

 tures on Natinal Philosophy, or Biot's, or Brisson's^ or any other 

 author's work on the same subject, in all of which that very aNioni 

 is mentioned and explained. In the instance above alluded to, 

 tlie passage was translated verbatim from a note in Dr. Magen- 

 die's pamphlet on the sul)ject of which I was commenting. — .'). 

 The reviewer, making himself quite merry, and rioting in the 

 pleasures of the discovery of the " Doctor's .sad error.?," asserts 

 that the specific gravity of a mixture of six volumes of water at I, 

 and one volume of acid at 0.705 S.'i, such as Magcndic cujploys, 

 must be 0.9900 : whereas, any person acquainted with tiic com- 



mon rules of alligation, would know that-^-^^ — i- — = 0.9579. 



To wliich I add that such is nearly the actual .specific gravity of 

 the mixture in question, ascertained l)y repeated experiments — 

 tiic " increase of density resulting from tiie mixture of liie j)uie 



acid 



