1825.] On the Formation of Ammonia, c. 149 



upon the same mixture ignited a second time, the proportion 

 diminished ; in a third operation it was sensible ; in a fourth 

 barely perceptible. The same mixture, however, by the ad- 

 dition of a new quantity of potash, again gained the power of 

 producing ammonia in two or three successive operations ; and 

 when any mixture had ceased to give ammonia, the power was 

 not restored by cooling it in contact with air. 



Sir Humphry Davy refrains from drawing conclusions from 

 these processes, observing with regard to the composition of 

 nitrogen in these experiments, that till the weight of the sub- 

 stances concerned and produced in these operations are com- 

 pared, no correct decision on the question can be made : I am 

 anxious to be understood as imitating the caution of one whose 

 judgment stands so high in chemical science ; and therefore 

 draw no positive conclusion from the experiment I have de- 

 scribed, or from the results I have yet to mention. As, how- 

 ever, I think they may lead to elucidations of the question, I 

 shall venture to give them, not with the minute detail of the 

 preceding experiment, but in a more general manner. 



Potash is not the only substance which produces this effect 

 with the metals and vegetable substances. Soda produces it ; 

 so also does lime and baryta, the latter not being so effective 

 as the former, or producing the phenomena so generally. The 

 common metallic oxides, as those of manganese, copper, tin, 

 lead, &c., do not act in this manner. 



Water or its elements appear to be necessary to the experi- 

 ment. Potash or soda in the state of hydrates generally con- 

 tain the water necessary. Potash, dried as much as could be 

 by heat, produced little or no ammonia with zinc ; but re-dis- 

 solved in pure water and evaporated, more water being left in 

 it than before, it was found to produce it as usual. Pure 

 caustic lime, with very dry linen, produced scarcely a trace of 

 ammonia, whilst the same portion of linen with hydrate of lime 

 yielded it readily. 



The metals when mixed with the potash appear to act by, or 

 according to their power of absorbing oxygen. Potassium, 

 iron, zinc, tin, lead, and arsenic evolve much ammonia, whilst 

 spongy platina, silver, gold, &c., produce no effect of the kind. 

 A small portion of fine clean iron wire dropped into potash 

 melted at the bottom of a tube, caused the evolution of some 



