1814.] On the Cause of Chemcal Proportions. 99 



course tlu's sulpburet is proportional to an oxide of arsenic still 

 unknown. 



In my former experiments I had alreadj' suspected the existence 

 of such an oxide, and 1 erideavoured to obt:iin it combined with 

 muriatic acid by distilling together muriate of lead and metallic 

 arsenic; but as the muri:\te of lead rci'iained undecomposed, the 

 oxide in question remained undiscovered. Having now such good 

 reasons for believing in the existence of this oxide, I made new 

 attempts to ohtaiu it. 1 put meiailic aise:;ic into a glnsi retort, 

 whicii I exhausted of air, ana then filled it with muriatic acid gas 

 previously dried over nKicury by means of num'ate of lime. I tlsen 

 heated the arsenic by means of a spirit of wine lamp. The arsenic 

 did not lose its metallic lustre; br,t the upp'T part of the retort 

 became coated with a flea-coloured crust, not metallic in its appear- 

 ance, and at first to a certain degree peUucid. The heat having 

 been continued for some minutes, the inside of tliis coating v;os all 

 covered with metallic, arsenic. When the retort was coded, I 

 expelled the muriatic acid gas, and filled the retort witii common 

 air. I cotdd not discover by the s-niell that the muriatic acid gas 

 was mixed with arsenical hydrogen gas. I poured water into the 

 crucible, but th.e brown coating was not altered. On adding a 

 little caustic potash ley, the crust detached Itself from the retort, 

 and was immediately converted into brilliant iiocks of metallic 

 arsenic. 



As this experiment was not conclusive, probably because the 

 water of muriatic acid dues not readily allow itself to be decomposed 

 by the metal, I substituted calomel in place of the muriatic acid 

 gas. With this 1 mixed pounded arsenic, and distilled the mixture 

 in a glasi retort furnished with ia receiver, 1 obtained some drops 

 of a white and smoking liquid, which, when mi\ed with a little 

 alkali, deposited arsenious acid : it was, therefore, acidi/m mi/riaticu'- 

 arsenicosina. In the neck of the retort there v/as deposited a red or 

 brownish red sublimate, which formed a tube, the inside of which 

 was coated with an amalgam of arsenic in a hplf jitjiiid state. The 

 red sublimate gave a yellow powder: it was entirely insoluble in 

 water. Mixed witli muriatic acid, and placed upon polislied copper, 

 it gave no mercurial stuin, as common muriate of nercury does. 



As tiiis sublimate contained evidently jwrtions of calomel upon 

 which the arsenic had not acted, 1 mlx«d it carefully with a new 

 portion of metallic arsenic, and sublimed it a second time. What 

 sublimed v/as at first of a fine red colour, and perfectly transparent, 

 Aftci wards it became deeper coloured and opaque. It was tiicn 

 easily detarbed from the retort, and lonstituted a brown mass 

 l)ordering upon yellow, without a crystalline fracture, and insoluble 

 in water, as before. Mixed with iron, and heatcfi, it gave out a 

 strong smell of arscuie, luul was converted into nuiriate of iron. 

 Hence it obviously contained muriate of arsenic. To obtain the 

 oxide of arsenic, 1 mixed the muriate with caustic potash. It 

 assumed a grey colour, and a metallic brilliancy; and after some 



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