of some Oxides of Mei-cury. 131 



It has been already said that the turf employed in the 

 manufactories of this country has some advantages over the 

 other kinds of fuel; and this remark is true, for an equal 

 heat may be easily and for a long time obtained, because 

 this matter burns slowly and in a very uniform manner. 



As charcoal, or tiie coals found in the bowels of the 

 earth, are the two combustibles employed most commonly 

 in France, none of the circumstances here mentioned must 

 be neglected when thev are used. 



By strictly observing all the precautions here indicated, 

 one will rarely fail to obtain oxide of mercury by nitric acid 

 of a brilliant red colour and well crvstalllzed. 



If the mercurial mass, notwithstanding all the care taken, 

 be not brilliant, or does not exhibit the crystalline aspect 

 required, it must be reduced to coarse powder and again 

 put into a new earthen vessel, at the bottom of which have 

 been placed some cubic centimetres of nitric acid only, in 

 order that the whole of the oxide which is not brilliant may 

 be slightly impregnated by heating it in a sand-bath. One 

 or two hours' exposure to heat under this apparatus will be 

 sufficient to convert the oxide into crystallized precipitate. 



Resuming what has been said on the method of preparing 

 red oxide of mercury by nitric acid, we see that the condi- 

 tions absolutely necessary for obtaining it constantly bril- 

 liant and crystallized are : 



1 st. To make choice of nitric acid without mixture of 

 muriatic acid. 



2d, To employ this acid at the degree of concentration 

 already indicated. 



3d, To evaporate the metallic solution in a moderate 

 heat. 



4th, To employ a vessel, the bottom of which is suf- 

 ficiently broad to make the oxidated mass of mercury pre- 

 sent a great deal of surface, and that it may be equally 

 heated with the greater ease in every point at the same time, 

 that the nitrate may be uniformly decomposed and may 

 pass as speedily as possible to tne state of red oxide. 



5lh, That the heat may be gradually increased, and in 

 proportion as the decomposition of the nitrate advances. 



Cth, That this temperature may be maintained the same 

 during ihe whole time of the operation, that is to say,dLiriug 

 the passage of the yellow to the red oxide required. 



" I am very far," says M. Paysse, " according to my 



experiments and those I have seen performed on a large 



scale, from believing that crystallized red oxide of mercury 



is indebted for this brilliant appearance to a slate of semi- 



I L' vitrification. 



