342 I Remarks on Arsenic. 



No. 6. Metallic zinc, brought into contact with a solution of arsenic 

 acid, precipitates the metallic arsenic at the negative pole. 



Arsenic acid, added to a solution of corrosive sublimate, and then 

 brought into contact with lime water, has not the least effect. 



Muriate of nickel and cobalt are equally indifferent to arsenic acid. 



After having now, with the prescribed hydrochemical tests, ana- 

 lyzed the fluid which we presume to contain arsenious or arsenic acid, 

 we are not yet able to decide, with certainty, as to the presence of 

 arsenic until we have pursued the analysis by the pyrochemical pro- 

 cess, or have effected the reduction by heat, in the following manner. 

 Both the precipitates obtained by lime water and sulphuretted hydro- 

 gen, and which have been laid aside in the former experiments, furnish 

 materials, by the aid of which we may draw a correct conclusion as 

 to the whole analysis. 



The arsenide of lime is to be dried, mixed with boracic acid and 

 charcoal, placed in a glass tube, and heated over a strong flame of 

 a lamp or a small charcoal fire. In this process, the boracic acid 

 forms borate of lime with the lime of the arsenide of lime, the oxy- 

 gen of the arsenious or arsenic acid combines with the charcoal to 

 form carbonic oxide and carbonic acid, and the arsenic sublimes in a 

 metallic state and lines the walls of the tube. 



The arsenide or arseniate of lime is also, according to Dr. Hare, 

 treated with prussiate of Mercury (the cyanuret of mercury) in which 

 case cyanogen, mercury, and arsenic are sublimed in gas and vapor, 

 the first goes off in the form of gas, the second is condensed in bril- 

 liant globular forms on the walls of the tube, and the third is per- 

 ceived by its peculiar smell and its appropriate metallic lustre, and 

 the arsenic is therefore, characteristically enough, distinguished from 

 the metallic mercury. 



The sulphuret of arsenic, obtained by sulphuretted hydrogen, with 

 arsenious or arsenic acid, is likewise to be dried and mixed with 

 equal parts of carbonate of potassa, or caustic potassa and charcoal, 

 and heated over the flame of a spirit lamp, where the sulphuret of ar- 

 senic is decomposed, and sulphuret of potassium is formed ; the oxy- 

 gen of the potassa combines with the carbon to form carbonic oxide 

 and carbonic acid, and the arsenic, in the metallic state, is sublimed 

 in the tube. 



Dr. Hare, in his experiments, used lampblack moistened with a 

 solution of caustic potassa. If now we have obtained from the re- 

 duction of the arsenide of lime and sulphuret of arsenic, the bril- 



