NftW MINERAL. 137 



As it was evident that the mineral under examination con- Useful applioa- 



1 /- 1 • 1 • ''°'* '^^ galvan- 

 tained oxide of zmc, and as the Usual mode of reducmg this ism in analysis, 



(particularly in minute quantities) is extremely difficult, the 

 process of reduction was varied in the following manner. It is 

 generally known, I believe, that by means of the galvanic appa- 

 ratus, the metals may be precipitated on each other from their 

 acid solutions without regard to the usual order of chemical 

 affinity : the objection to the application of this process, as a 

 means of analysis^ arises from the quick re-absorption of the 

 precipitated metal by the disengaged acid from which it had 

 just been separated : but, as Mr. Klaproth has lately observf 

 ed that the metals may be precipitated by each other from the 

 alkaline solutions of their oxides in the order of their chemical 

 affinity, a portion of oxide of zinc was dissolved in aqua kali, 

 and by means of the galvanic apparatus a precipitation of me- 

 tallic zinc was very readily obtained on plates of iron, copper, 

 and platina ; in this experiment it was accidentally observed, 

 that upon withdrawing the communication with the galvanic 

 apparatus, the recently precipitated zinc was soon re-dissolved 

 by the aqua kali , and not only by the portion of aqua kali, 

 employed in that experiment, but by any other portion also, 

 or even by a solution of sub-carbonate of ammonia ; however, 

 by not interrupting the communication, the precipitate remain- 

 ed ; and in this way, four parts out of five of metallic zinc were 

 recovered from a solution ©f its oxide in aqua kali. The re- 

 absorption of the zinc by the aqua kali at first appeared to take 

 ])lace without any effervescence ; but upon a closer examina- 

 tion, jninute air-bubbles were seen detaching themselves from 

 the surface of the zinc ; if these were bubbles of hydrogen gas, 

 as probably they were, originating from the decomposition of 

 the water, an easy explanation is afforded of the solution of the 

 zinc. 



By the foregoing experiments were obtained the means of 

 ascertaining, both by calculation and actual reduction, the pro- 

 portion of zinc in a given weight of its oxide. In order to 

 ascertain the quantity of sulphur acidified during solution in 

 nitric acid, the following experiment was made : 



Sulphur, grs. 7-f"o , were boiled in nitric acid till the whole To ascertain 

 of the sulphur had disappeared : a solution of nitrate of baryt J^f h«r"a'cidifi» 

 v/as then added till there was no longer any precipitation ; the ed by solution 



VeL. XIV,— June, 1S06, T precipi- ^"^'^"' ^"'*' 



