HISTORY OF PRUSSIATES. %$ \ 



Prussiate of mercury is obtained, as is well known, by Prussiate of 

 treating red oxide of mercury with prussian blue. This salt mer 

 easily crystallizes in tetraedral prisms. It is always opake. 

 It may retain potash, as will be seen presently, if there were 

 any in the prussian blue. It equally retains oxide of iron, as 

 may be seen by the following experiment. Heat a few grains 

 with muriatic acid in a little matrass, and white prussiate 

 will be precipitated. 



To free it from iron, its solution must be boiled with red Freed from 

 oxide of mercury repeatedly : each time it deposits oxide of ir * 

 iron, but this depuration is tedious. The prussiate of mer- 

 cury changes its state by being boiled with red oxide, and 

 appears to take up a surcharge ; for it no longer crystallizes 

 in prisms, but in small groupes of very fine needles. Then 4 

 solutions too require to be farther concentrated; and dis- 

 solving the crystals afresh does not bring them back to their 

 original figure. 



This salt heated in a retort is easily and wholly decom- Decomposed 

 posed, if the fire be not urged too strongly. It is sufficient by heat# 

 to heat a few grains in a tube of three or four lines diameter, 

 closed at one end. If, while thus heated, the open end be 

 exposed to flame, the prussic gas mingled with gaseous 

 Oxide of carbon takes fire. The flame is red and blue, ter- 

 minated by a yellowish aureola. One hundred grains of 

 prismatic prussiate gave one time seventy-two grains of mer- 

 cury, at another seventy-two and half. The residuum of 

 eight or nine grains was a mixture of charcoal and carbo- 

 nate of potash. This is nothing extraordinary, for the alkali 

 cannot decompose prussiate of mercury, and no doubt it 

 was contained in the prussian blue, which was that of the 

 shops. 



The products that arose in this distillation were ammonia; Product?. 

 oil, and this even in tolerable abundance \ and a mixture of 

 Carbonic acid gas, and carbonic oxide. 



There does not appear to be any prussiate of mercury The oxide of 



with oxide at a minimum for its base ; for the prussic acid inercur y al * 



i ... wavs at a wax- 



applied to mild muriate of mercury, or to the nitrate with base imum. 



at a minimum, eliminates a portion of the mercury, and pro- 

 duces a prussiate with base of red oxide, like that obtained 

 directly by treating red oxide with the acid, 



S 2 The 



