282 On a new Mode of preparing arsenicnted Hydrogen Gas. 



The arseniuret, which seems to me quite analogous to the alka- 

 line phosphuret, decomposes waiter as soon as it conies in con- 

 tact with it, and from this decomposition results avsenicated 

 hydrogen gas, which disengages itself, because, similar to phos- 

 phuretted hydrogen ga*;, it docs not possess any acid properties. 

 1 believe it, too, to be identically the sanie with the giis which is 

 obtained by heatinsr the arseniuret of tin with hydrochloric 

 acid. One portion of liquid which was very alkaline, being fil- 

 tered and supersaturated with liydrochloric acid, yielded but a very 

 slight yellow precipitate with hydrosulphate of potash, and only 

 discoloured a very small quantity of the red sulphate of man- 

 ganese. Another portion of liquid was saturated with acetic 

 acid, then evaporated to dryness, and treated with very concen- 

 trated alcohol. The acetate of potash was found to predominate 

 in the base, although the two salts were originally neutral, and 

 the residue consisted of arseniate acid of potash. A similar di- 

 vision was obtained by evaporating neutral arseniat of potash, 

 which never crystallizes so well as when combined with an ex- 

 cess of acid, and then it is analogous to tartrate of potadi. 



It is remarkable enough that hydrogen gas does not combine 

 with arsenic when potash is made to act on that metal, while it 

 combines verv well with it when the arseniuret of tin is decom- 

 posed by hydrochloric acid. I apprehend that this difference is 

 owing solely to the temperature, Avhich is much greater in the 

 first case than in the second ; for I am certain that by a spirit 

 of wine heat arsenicated hydrogen gas may be decomposed. It 

 }s nearly the same u-ith caibonetted hygrogeu gas ; — if it is pre- 

 pared at an ordinary temperature it contains a considerable 

 quantity of carbon, and very little or none at all when obtained 

 .at an elevated temperature. 



In the preparation of phosphuretted hydrogen gas by potash, 

 a gas is often obtained which has not the property of inflamma- 

 bility when in contact with the air, and v.hich j:)robably is some- 

 times pure hydrogen. Is it not probable that this may also pro- 

 ceed from too high an elevation of temperature ? For phosphu- 

 retted hydrogen gas is easily decomposed by heat, and that wliich 

 is obtained by the dissolution of phosphurets in water is always 

 ituj)re charged with phosphorus than that which is produced by 

 heat. I may remark, that although arsenicated, phosphuretted, 

 or carburetted hydrogen gas is decomposed at a temperature 

 which may be supposed little difierent from red heat, it does not 

 follow that hydrogen gas ought necessarily to combine with ar- 

 senic, phosphorus and carbon, at a temperature a little inferior; 

 for there is always a distance more or less great between the 

 temperature necessary to effect a combination, and that which 

 IS sufficient for a decomposition. 



Arsenic 



