30 Klaproth on the Chemical Analysis 



nation of this ore, and being unable to obtain satisfactory 

 results by any humid process, I proceeded as follows : — 



a. 200 grains of finely pulverized fahlerz were heated to 

 redness in a small glass retort ; the neck of the retort contained 

 after this operation 17 grains of red sulphurct of arsenic. 



b. The residuary ore had fused into a lead-gray mass ; it was 

 pulverized, mixed with half its weight of charcoal powder and 

 submitted to a second sublimation, the retort being kept at a 

 bright red heat for one hour ; it thus afforded a crystallized 

 sublimate of pure arsenic, weighing 22.5 grains. 



c. The residue was now taken out of the retort and exposed 

 upon a red-hot plate so as to burn away the charcoal, during 

 which the fumes of arsenic were also perceived to escape. After 

 this operation the residuary ore weighed 146 grains, so that it 

 had sustained a loss of 54 grains, which, however, cannot be 

 regarded as correctly indicating the loss of arsenic and sulphur, 

 since it is probable that during the combustion of the charcoal 

 a portion of oxygen was absorbed so as to increase the weight 

 of the residue. 



d. The roasted ore was now digested in nitric acid diluted 

 with its weight of water, and the blue solution passed through 

 a filter, upon which there remained 7 grains of a mixture of 

 charcoal and red oxide of iron, which being separated by muri- 

 atic acid, 3 grains of charcoal remained. 



e. On adding the muriatic solution of iron to the preceding 

 nitric solution, a portion of muriate of silver was thrown down, 

 which being carefully collected and reduced, afforded 0.80 

 grains oi silver. 



f. The solution was now mixed with sulphuric acid and 

 evaporated to dryness ; the residue was perfectly soluble in 

 water, so that it contained no lead. Excess of ammonia was 

 therefore added, which separated oxide of iron, weighing after 

 having been dried, mixed with oil and ignited, 45 grains ; and 

 being perfectly attractable by the magnet. 



g. The dark-blue ammoniacal solution, supersaturated 



