128 On the mamifacturlng, on a large Scale^ 



the shops, presents a powerful obstacle when in too strong 

 proportions. 



Bv dissolving mercurv in nitric acid mixed with muriatic 

 acid there is almost always Formed a white precipitate, which 

 is the more abundant as the quantity of that acid is greater. 

 Without attemptintr at present to determine the real nature 

 of this precipitate. M. Paysse considers onlv the part which 

 this combined substance performs in the oxidation proposed 

 to be given to the mercury by decomposing the nitrate of 

 that basis by the action of heat. 



If crystallized nitrate of mercury, arising from a solution 

 of that metal in nitric acid n)ixcd \\ ith muriatic acid, be 

 exposed to heat, this salt first begins to lose its water of 

 crystallization; it is then decomposed, suffering to escape 

 a portion of acid which it contained in excess, and which 

 may be collected bv means of a proper apparatus, because 

 it has experienced no alteration. This disengagement is 

 succeeded by that of gaseous nitrous acid, wdiich is mani- 

 fested by very elastic red vapours. I'his acid gas is almost 

 always mixed with oxide of azote, or the l;>cter follows the 

 disengagement of the former. These two gases indicate 

 the decomposition of the nitric acid, which gives a portion 

 of its oxygen to the mercury, and is thereby brought to the 

 nitrous state, or to that of oxide of azote. By continuing 

 the heat, the last [lonions of the nitric acid abandon the 

 mercury, and the latter is converted into an oxide more or 

 less saturated with oxvgen ; indeed, its production seems to 

 depend on the quantity of caloric which is accumulated 

 on that substance during its passage to the state of red 

 oxide. % 



When the vapours of the nitrous gas cease, the oxide 

 changes its colour, passing successively from white to yel- 

 low, from yellow to orange, and from orange to red, more 

 or less intense. It is generally when the red is very bright 

 and beautiful that the vessel is ijiken from the fire, and the 

 mass is then preserved as it is, or reduced to powder. 



It would seem, on the first view, that an operation con- 

 ducted as above ought to give, for constant product, an 

 oxide well crystallized. This, indeed, is the ease, 1st, When 

 the nitric acid is free from muriatic acid, or when the latter 

 is in very small quantity : cd, When its density is equal to 

 34 or 38 degrees; 3d, When the desiccation and decompo- 

 sition of the metallic nitrate have l^een efiectcd slowly and 

 i)i an uniform manner ; tth, And when the heat employed 

 towards the end of the operation, and while the last por- 

 tions of the acid disunite, has been graduated and main- 

 2 taine-d 



4 



