246 Dr Turner on the Cyanuret of' Mercury, 



powder, and one of the peroxide of mercury, should be boiled 

 in eight parts of water until the colour of the mixture, from 

 being blue, becomes yellow. The solution, after being filtered, 

 is evaporated by heat and cooled alternately, in order to obtain 

 the cyanuret of mercury in the form of crystals. As the com- 

 pound, thus procured, always contains oxide of iron, Proust 

 recommends, with the view of freeing it from the iron, that the 

 crystals should be redissolved in water, and boiled with an ex- 

 cess of the peroxide of mercury. Hydrocyanic or muriatic 

 acid is then added to neutralize the solution, and the purified 

 cyanuret of mercury is separated as before by crystallization. 



In making the cyanuret of mercury by this process, I always 

 find considerable difficulty in procuring it free from iron. The 

 solution, from the commencement, though the best Prussian blue 

 which I could purchase in Edinburgh is employed, has uniform- 

 ly a deeper colour than can be well produced by a small quan- 

 tity of iron rendered soluble by the cyanuret of mercury ; and 

 on separating the cyanuret as much as possible by crystalliza- 

 tion, a yellow solution remains, which has no disposition to crys- 

 tallize. Suspecting, from these circumstances, that the incon- 

 venience of the process is owing to impurities contained in 

 the Prussian blue, I boiled some of that substance in muriatic 

 acid diluted with nine or ten times its weight of water, collect- 

 ed the insoluble matter on a filter, and edulcorated. From the 

 colour of the acid solution, it was obvious that it contained 

 iron ; and, accordingly, on adding an excess of pure potash, 

 the hydrous peroxide of iron was thrown down in large quan- 

 tity. On filtering the alkaline solution, and boiling it with 

 muriate of ammonia to neutralize the potash, a copious preci- 

 pitate of alumina took place. These substances appear to ex- 

 ist in the Prussian blue, as subsalts of sulphuric acid ; at least 

 pure water did not take up a trace of iron, whereas the solu- 

 tion made by dilute muriatic acid was precipitated copiously 

 by muriate of baryta. 



"When the purified Prussian blue and the red oxide of 

 mercury, in due proportion and in fine powder, are boiled 

 together with water, the former is entirely decomposed, and a 

 perfectly colourless solution is obtained, which yields, by eva- 

 poration, pure crystals of the cyanuret of mercury, even to 



