of Copper and of Iron. 219 



than three, yet three are much kfs than one. This ophiion, 

 that hydrogen is really the reduftive, is the more extraordi- 

 nary, as it" is not founded on the iingle experiment above 

 mentioned. 



If a bit of zinc (or tin, or iron,) is thrown into a folution 

 of oxide of arfcnic in water, no change of any kind will be 

 etfeeled, even after a confiderable time : but the inltant that 

 muriatic acid is added, effervefcence and precipitation com- 

 mence; a few minutes futfice to obtain all the arfenic in its 

 metallic ftate. It may be objecled here, that muriatic acid 

 (as muriatic acid) produces fome hitherto unknown modi- 

 fication in the order of cftabliftied affinities. This obje6lion 

 is not plaufible ; and I can adduce fo clear an anfvver to it, 

 as to Ihow that it is of very little moment. If aqueous arfenic 

 acid is uft d inftead of the above folution, the fame pheno- 

 mena of effervefcence and precipitation enfue as when mu- 

 riatic acid had been ufed in the former cafe ; and that precife 

 quantity of metallic arfenic is thrown down, which can yield 

 fufficient oxygen to the zinc to combine with the remaining 

 acid undecompofed. The precipitate which is formed, is a 

 mixture of metallic arfenic with arfeniate of zinc; and thefe 

 may be feparated by muriatic acid, which will dilTolve the 

 metallic fait, without acting upon the arienic. 



If, inftead of muriatic acid, fulphuric acid is ufed, the 

 fame phaenomena take place, in a lei's degree. But, it the 

 experiment is tried with nitric acid, there is no difengage- 

 ment of hydrogen gas; and the metals eflcC;!: a precipitation 

 with much lefs rapidity and certainty than in the fornier cafe. 



It is very true, that hydrogen, in its nafcent ftate, m.ty 

 have properties with which we arc yet unacquainted ; and 

 mav determine combinations, which it can in no other ftate 

 produce. Jiut the decompolition of water, in the firft in- 

 ftance, in order that a new recomi)ofuion niay, at that mo- 

 ment, be cff(2£lcd by the fame agents, is in itlclf lufticiently 

 paradoxical. 



The facts laft mentioned are foinewhat analogous to, and 

 feem even confirmative of, a theory propofed fouie time paft 

 by Mrs. Fulhaine; but 1 fliall withliold my full all'ent, both 

 to her explanation and to any I could give, until ihcfe cvir 

 dent contradictions can in fome way be further elucidated. 



In the analvfis of every ore in which tlic metal is com- 

 bined with fulphur, I have found much variation in the 

 quantity of the Liltrr which mav be obtained, even in cx|-ve- 

 riu.ents upon the fame fpecimen. If nitric acid is ulcd not 

 fii(Ticiently Hmng, part of the ore remains untouched, and 

 will rt^uire fnblequcnt treatment, always dlfadvanta^' fous in 



delicate 



