the Decomposition of the Earths, &c. 205 



cone was strongly alkaline ; the two fluids were passed 

 through bibulous paper, and mixed together, when a pre- 

 cipitate fell down, which proved to be silex. 



On the first view of the subject, it appeared probable that 

 this silex had been formed by the union of the acid and the 

 alkaline matter in the two cones, and that the experiment 

 demonstrated a decomposition and recomposition of silex; 

 but before such a conclusion could be made, many points 

 were to be determined. 



It was possible that the acid might be nitric acid, pro- 

 duced as in other electrical experiments of a similar nature, 

 and that this acid might have dissolved silex, which was 

 precipitated by the alkaline matter at the other pole, which 

 might be either potash used for dissolving the silex, which 

 had adhered to it, notwithstanding the processes of lixivia- 

 tion in acids, or ammonia produced in consequence of the 

 presence of the atmosphere ; or if potash was present, it was 

 likewise possible that the silex might have been carried over 

 in solution, with this alkali, from the positive to the nega- 

 tive surface. 



Minute experiments were instituted and completed in the 

 same manner as those detailed in the Philosophical Trans- 

 actions for 1807j p. 7*, which soon proved that there was 

 no reason to suppose that the silex had been changed in 

 these experiments. 



The acid proved to be nitric acid, which under the elec- 

 trical action seemed to have dissolved the silex; the alkali 

 turned out to be principally fixed alkali ; and that it was 

 merely an accidental ingredient, and not a constituent of 

 the silex, appeared from this circumstance, that when the 

 same portion of silex was long electrified, by degrees it losi 

 its power of affording the substance in question f. 



This 



* Phil. Mag. vol. xxviii. p. 6. 



■J- If silex that has been carefully washed, after precipitation by muriatic 

 acid from liquor silicum, be moistened, and acted on by mercury negatively 

 electrified, the mercury soon contains a notable quantity of potassium. Well 

 washed alumine that has been precipitated from alum by carbonate of soda, 

 affords by the same treatment sodium and potassium, so that the powers of 

 electrochemical analysis are continually demonstrating the imperfection of 

 the common chemical methods of separating bodies from each other. The 



purest 



