PRIMARY AND SECONDARY RESULTS OP ELECTROLYTIC ACTION. 95 



747. But when we take to our assistance the law of constant electro-chemical action 

 ah'eady proved with regard to water (732.), and which I hope to extend satisfactorily 

 to all bodies (821.), and consider the quantities as well as the nature of the substances 

 set free, a generally accurate judgement of the primary or secondary character of the 

 results may be formed : and this important point, so essential to the theory of electro- 

 decomposition, since it decides what are the particles directly under the influence of the 

 current, (distinguishing them from such as are not affected,) and what are the results 

 to be expected, may be established with such degree of certainty as to remove innu- 

 merable ambiguities and doubtful considerations from this branch of the science. 



748. Let us apply these principles to the case of ammonia, and the supposed deter- 

 mination of nitrogen to one or the other electrode (554. 555.). A pure strong solution 

 of ammonia is as bad a conductor, and therefore as little liable to electro-decompo- 

 sition, as pure water ; but when sulphate of ammonia is dissolved in it, the whole be- 

 comes a conductor ; nitrogen almost and occasionally quite pure is evolved at the 

 anode, and hydrogen at the cathode ; the ratio of the volume of the former to that of 

 the latter varying, but being as 1 to about 3 or 4. This result would seem at first to 

 imply that the electric current had decomposed ammonia, and that the nitrogen had 

 been determined towards the positive electrode. But when the electricity used was 

 measured out by the volta-electrometer (707- 736.), it was found that the hydrogen 

 obtained was exactly in the proportion which would have been supplied by decomposed 

 water, whilst the nitrogen had no certain or constant relation whatever. When, upon 

 multiplying experiments, it was found that, by using a stronger or weaker solution, 

 or a more or less powerful battery, the gas evolved at the anode was a mixture of 

 oxygen and nitrogen, varying both in proportion and absolute quantity, whilst the 

 hydrogen at the cathode remained constant, no doubt could be entertained that the 

 nitrogen at the anode was a secondary result, depending upon the chemical action of 

 the nascent oxygen, determined to that surface by the electric current, upon the am- 

 monia in solution. It was the water, therefore, which was electrolyzed, not the am- 

 monia. Further, the experiment gives no real indication of the tendency of the ele- 

 ment nitrogen to either one electrode or the other ; nor do I know of any experiment 

 with nitric acid, or other compounds of nitrogen, which shows the tendency of this 

 element, under the influence of the electric current, to pass in either direction 

 along its course. 



749. As another illustration of secondary results, the effects on a solution of acetate 

 of potassa may be quoted. When a very strong solution was used, more gas was evolved 

 at the anode than at the cathode, in the proportion of 4 to 3 nearly : that from the anode 

 was a mixture of carbonic oxide and carbonic acid ; that from the cathode pure hydrogen. 

 When a much weaker solution was used, less gas was evolved at the anode than at the 

 cathode ; and it now contained carburetted hydrogen, as well as carbonic oxide and car- 



1804, torn. li. p. 174.), who stated that the metals were evolved directly by the electricity : in which opinion it 

 appears, from that time, Davy coincided (Philosophical Transactions, 1826, p. 388.)- 



