130 On the rna/ntfacturing, on a large Scale, 



tion, uhat is the quality of the nitric acid employed, and 

 the process to be followed in the application of heat durino; 

 the wliole time of the operation, the author can with cer- 

 tainty indicate a process for obtaining this oxide provided 

 with all the qualities required in it, and which are sought 

 for in manufactories. 



Take mercury, free from every other metallic matter, 50 

 kilogrammes ; nitric acid, deprived as much as possible of 

 muriatic acid*, and of from 34 to 38 degrees, 70 kilo- 

 grammes ; dissolve the metal in the acid, and assist their 

 reciprocal action by a gentle heat in a s-and-bathf ; evaporate 

 by distillation, and take the receiver from the retort when 

 the vapours of the nitrous gas begin to manifest themselves, 

 as they announce the decomposition of the mercurial ni- 

 trate. The point here is to employ a constant and mode- 

 rate temperature, if you wish to ensure success to the ope- 

 ration X- it is raised a little towards the end, that is to say, 

 when the disengagement of the gaseous nitrous acid is no 

 longer manifested, but in a manner not very sensible : the 

 vessel must be exposed to this degree of heat till it is ob- 

 served that the mass of red mercurial oxide is of a bright 

 and brilliant red colour in all its parts. Eight hours of heat 

 are in general sufficient for 200 kilogrammes of this sub- 

 stance. 



* It may be tried by nitrate of silver, and if the quantity of muriatic acid 

 appears weak it is neglected. It sometimes happens, however, and particu- 

 larly when the nitric acid is too weak, or when the quantity is not sufficient, 

 that the mercury is precipitated in a white oxide in proportion as it is formed, 

 because it cannot be held in solution either by the water or by the remaining; 

 acid, and that the unoxidated mercury besides continually exercises a che- 

 inical attraction on one of the principles of the acid, and that the latter tends 

 rather to be decomposed than to dissolve the mercury, already saturated with 

 oxygen to a certain degree ; so that care must be taken not to coi-vfoimd this 

 property with that of the muriatic acid : moreover the precipitate, which is 

 not the effect of the oxidation of the mercury, dissolves entirely in the heated 

 nitric acid, while the other can dissolve only in very small quantity : this 

 property alone would be sufficient to distirjguish it. I might have dispensed 

 with making this observation, since in my process I requii e a very pure and 

 highly concentrated acid •, but as it often happens that acid sufficiently stron"- 

 cannot be procured, this deficiency may be supplied by quantity, and my 

 remark in this case cannot be here misplaced. — kote of M. Pfiyssv. 



f This solution must be made in a glass retort, the bottom of which is 

 broad. This vessel is preferable to the matrasses employed in Holland, be- 

 cause the only question here is to adapt t:i it a receiver, and to distil in order 

 to collect the acid which is not decomposed on the metal. This object is by 

 no means to be neglected in operations on a large scale. — Note ofM. Payssi: 



I The author v, ished to have been able to determine in a precise manner 

 the degree of heat which ought to be applied to the oxide of mercury to give 

 it the red colour as well as brilliancy ; but this was impossible, because ho 

 «vas not provided with a pyrometer. 



It 



