AQUEOUS AND ALCOHOLIC SOLUTIONS. 159 



so far as observed, might not arise from an oxyacid formed by secondary action at 

 the positive. All such objections are, however, obviated, by placing the poles be- 

 yond the solution, so as to get quit of secondary actions ; and we thus readily ob- 

 serve the transference of acid in all cases in which it takes place, by saving it from 

 secondary decomposition. In this way I shewed, in numerous instances, that acid 

 and alkali went to their respective poles, and that the acid, passing, was the 

 hydracid. These facts, wherever they are observed, are, I apprehend, quite suffi- 

 cient to prove the haloid to be dissolved as a hydracid salt ; for, even laying aside 

 for a moment the experiments by which I have endeavoured to shew that the ha- 

 loids, if existing as such in water, are not directly decomposed, let us take the 

 different views of the nature of the galvanic action which suggest themselves when 

 both poles are plunged into the solution in the ordinary manner, and consider them 

 on the supposition that haloids are dissolved as such. 



First, let us suppose that only one of the two substances water or haloid, 

 it matters not which is decomposed, it is evident that we cannot account for 

 the production of acid, where secondary action is excluded. Next, let us suppose 

 that both substances are decomposed, and that either the elements, going to the 

 same pole, unite on their journey, or, by an interchange of elements, the oxygen 

 of water unites with the metal of the haloid, and the hydrogen of the water with 

 the electro-negative constituent of the haloid. The former of these alternatives is 

 contradicted by the fact that the acid formed is a hydracid ; and the latter, although 

 it might account for the formation of acid and alkali, would not account for the 

 liberation of the electro-negative constituent of the haloid at the positive pole, and 

 of hydrogen in fixed and definite proportion at the negative, whatever be the 

 strength of the solution. It appears to me, then, to be sufficient, in order to prove 

 the aqueous solution of a haloid as a hydracid salt, to shew the separation of the 

 hydracid by voltaic action, under circumstances which exclude secondary action. 



It must, however, always be remembered, that although such production can 

 be readily shewn in many cases of haloids, it does not necessarily follow that this 

 should hold in all cases. We are, of course, best prepared to expect it in the case 

 of haloids, of which the constituents have the strongest affinities for oxygen and 

 hydrogen, such as the ordinary haloids of the bases of the alkalies and alkaline 

 earths. And, accordingly, I shewed that it applied to chlorides and iodides of 

 potassium and calcium. But farther, it was found to hold good in regard to the 

 ordinary haloids of the common metals of strong affinities, such as zinc. I was 

 prepared, however, to consider it as doubtful what might be the result in regard 

 to those of the noble metals. Accordingly, when a moderately strong solution of 

 chloride of gold was placed in the tube B*, and connected by asbestos with the 



* Fig. 3, PI. II. Edin. Trans, xiv. 

 VOL. XV. PART I. U U 



