358 Berzeliiis's Experiments to determine the Composition [May, 



explained — it appears clear, I say, that we shall then have a key 

 to explain similar anomalies, exhibited even by the acids of 

 phosphorus and arsenic ; though such an explanation may have 

 little probabihty at present. 



Experiments rendering the Existence of an Oxide of Arsenic 

 probable. — Some authors pretend that metallic arsenic exposed 

 to the influence of the air falls into a black non-metallic powder ; 

 and Bergman advises us to keep arsenic under water. I had an 

 opportunity of verifying <^his property of arsenic in an experiment 

 in which 100 arsenic in a vessel covered with paper, after an 

 interval of some months, had acquired almost eight parts in 

 weight, and afterwards ceased entirely to acquire more. The 

 black powder thus produced was insoluble both in water and in 

 acids ; but when digested in muriatic acid, it assumed the 

 metallic lustre, and the acid was found to contain arsenious acid 

 in solution. When strongly heated, it gave out in the first place 

 arsenious acid, and then left a residue of metaUic arsenic. In 

 short, this powder possesses the characters of the class of oxides, 

 to which 1 have ventured to give the name of suboxides ; and 

 which, without being able to combine with other oxidized 

 bodies, are decomposed by very slight forces, a portion of their 

 radical being reduced, while another is carried to a higher and 

 more stable degree of oxidation. 



As the quantity of oxygen found in this suboxide is a fourth of 

 that of arsenious acid ; without, however, being likewise a 

 simple submultiple of the oxygen in arsenic acid, I wished to 

 examine its composition anew ; but to my great surprise, I was 

 unable to procure arsenic, which falls in powder in the air. I 

 have small quantities of metaUic arsenic exactly weighed, which 

 have remained for three years in glass vessels covered with 

 paper, and which have not acquired any additional weight. I 

 do not know what constitutes the difference between the metallic 

 arsenic, which falls to powder, and that which remains unaltered, 

 nor have I any idea of the different processes to be followed in 

 order to obtani the one or the other. 



I endeavoured then to produce an oxide of arsenic in combi- 

 nation with an acid. I heated arsenic in a phial filled with 

 muriatic acid gas. The arsenic underwent no change ; but a 

 small quantity of puce-brown matter sublimed. The muriatic 

 acid gas was not absorbed, and no smell of arseniuretted hydro- 

 gen gas was perceived when the gas was passed into the air. 

 the brown matter was not altered by water ; but on adding a 

 little caustic potash, it detached itself immediately from the 

 glass, recovered its metalhc lustre, and fell into light scales 

 which swam in the liquid. This experiment seems to indicate 

 an action between muriatic acid gas and arsenic, though too 

 weak to draw any certain conclusions from it. I then mixed 

 three parts of calomel with one part of metallic arsenic, and 

 distilled them together. There were formed in the first place 



