'J'2 ON GALVAKISM. 



Nor the decom- When pure ammonia is expofed to the galvanic a6tion, we 

 poiUion of am- \^^yQ ^s before, hydrogen from one wire, and nitrogen from 

 monid explained. ' tt i /• i r^- i i • j ^u 



the other. How can thefe productions be explamed upon the 



principle of Dr. Gibbes ? 



This theory fup- This able phyfician further obferves that oxydation is a com- 

 pofes oxidation bination of water with the metallic body, confonant to the 



to be the addi- . r-n-r^^ -.tt . . 



tion of water opmions ot Prieuley, Watt, and others. 



and fubtraftion When a galvanic pile is placed under a receiver fituated 



of eledlncity. , •, . i • r l u • 



But the pile re- Over water, while the galvanic procels goes on, by having a 

 quires oxigen metallic circuit from the top to the bottom plate, a lofs of air 

 ph^el ^^'""■^' enfues, and which is found to be the pure part of atmofpherie 

 air: if the pile be placed in an exhaufted receiver, the galva- 

 nic procefs is very trivial, and the plates very flightly oxydated. 

 How upon the principles of Dr. Gibbes can we explain thefe 

 phenomena? If oxydation be merely the combination of water 

 with the metal, why (hould the pure part of atmofpherie air 

 be thus feparated while the metals are in immediate contadl 

 * with fo much water? 



Oxidation ap- Whether galvanifm be the caufe or the efFe6l of the chemical 

 pears to require change induced in the metallic fubftance, they appear tome to 



thedifeni:age- » r , /- -, i • i • 



ment of ekftri- be contemporaneous relults, fimiiarto what appears in theim- 

 *="^y* merfion of iron in a folution of the fulphate of copper, and 



whether the iron be ditTolved prior to the copious precipitation, 

 no experiments I am aware of can decide. From various 

 circumftances it appears that oxydation cannot take place un- 

 lefs the combined eledtricity of the metal be capable of being 

 Dr. Afh*sex« difengaged. This is rendered evident in a very happy experi- 

 perimcnt. ment of Dr. Afli, who having been the alTociate of the much- 



lamented Humboldt* in his fcieniific purfuits, may now be 

 deemed more acquainted with the minutiae of galvanifm than 

 any other perfon. This gentleman has remarked that when a 

 plate of zinc is immerfed in a weak folution of fulphuric acid 

 and water, a decompofition takes place, the oxygen bafe com- 

 bines with the metal, while tlie hydrogen is difengaged in a 

 gafeous ftate. When a plate of filver is immerfed, no decom- 

 pofition lakes place ; the very inftant a conta6l is eiFedted be- 

 tween the two metals, whether by portions out of the fluid or 

 in the fluid, then the filver is immediately a6ted on and dif- 

 engages hydrogen alfo, and itfelf becomes oxydated. 



* Humboldt died lately at Acapulco, of the yellow fever, while 

 attempting to perfetil his geological obfcrvationSt 



In 



