Analysis of Scientific Books. 401 



acid i8, it has found its way into the apothecaries* shop, and 

 has long been used in one form or other ; but the merit (whateve? 

 it may be) of using the pure acid, duly diluted, as a substitute 

 for the less definite and certain combinations of it, belongs 

 chiefly to Mr. Magendie, to whose essay formerly published in 

 this Journal we have already adverted ; and to the author now 

 before us. 



Dr. Granville proceeds in the first and second sections of his 

 book, to treat of the chemical history of the prussic acid ; and, 

 after adverting superficially to the discovery of Prussian blue, 

 and to the researches of Gay-Lussac, Scheele, and others, 

 points out the methods usually employed for preparing this 

 substance for pharmaceutical use. He gives us the pro- 

 cesses of Scheele, Vauquelin, and Magendie, and, lastly, that 

 of the Apothecaries' Company ; and without any sufficient re- 

 marks upon the principles of these processes, passes judgment 

 (not always tempered with mercy) upon their respective merits. 



Scheele*s process consists in boiling Prussian blue with red 

 oxide of mercury and decomposing the solution of cyanuret of 

 mercury thus obtained by nascent hydrogen gas ; that is, by 

 mixing its solution with iron filings and sulphuric acid, and 

 proceeding to distillation; the prussic acid passes over in 

 aqueous solution, and may be rendered more pure by re-distil- 

 lation with a little chalk. 



This is not a bad process, provided Prussian blue were al- 

 ways of equable purity, but as it is a very heterogeneous com- 

 pound as usually found in the shops, the liquid obtained by 

 boiling it with oxide of mercury, is of variable composition ; 

 those processes, therefore, are preferable, in which the pure 

 cyanuret is used. 



Vauquelin's process is directed in the Paris Phai-macopoeia, 

 and is, in our opinion, extremely objectionable. It consists, in 

 decomposing solution of cyanuret of mercury by sulphuretted 

 hydrogen gas, filtering to separate the sulphuret of mercury 

 thus produced, and adding carbonate of lead to remove the re- 

 maining sulphuretted hydrogen. The prussic acid remains dis- 

 solved in tlie filtered liquor. 



