ON PYROXYLIC SPIRIT, &c. 121 



evolved at its proper pole, being employed in there producing secondary effects 

 either on the solvent or the dissolved body. 



When an ordinary oxy-acid salt, of a powerful base, such as nitrate of lime, 

 is dissolved in absolute alcohol, the acid and base go to then- proper poles under 

 voltaic agency, as in a similar aqueous solution, but much more slowly, efferves- 

 cence taking place at the negative pole, and little or none at the positive. Where 

 the base is not of difficult reduction, as in nitrate of zinc, the evolution of gas at 

 the negative pole is diminished, and metal reduced by hydrogen separates at that 

 pole, mixed with oxide. 



When an acid whose elements are strongly united, as boracic acid, or an 

 alcali, as potash, is held in solution, effervescence appears at the negative pole, 

 but none at the positive, unless in the case of a strong solution of a hydrated 

 alcali, when a slight evolution of gas also occurs at the positive pole ; and in these 

 cases, appearances do not indicate any decomposition of the dissolved body. 

 When an alcoholic solution of a haloid salt is acted on, no gas is evolved from the 

 positive pole ; but in the case of an iodide there is immediate separation of iodine 

 at that pole, which is dissolved by the solution, giving it a deep red colour. 

 When the metal of the haloid salt is one of powerful affinities, as potassium, cal- 

 cium, or magnesium, there is brisk evolution of hydrogen, and more or less ap- 

 pearance of the oxide of the metal at the negative pole ; metal appearing in that 

 case to be first reduced by a portion of the nascent hydrogen, which combines 

 with the electro-negative element of the haloid, and then to react on the water 

 of the alcohol ; and a portion of the oxide, when it is soluble in alcohol, being 

 also drawn from, the positive pole, where it has been formed by another secondary 

 action. Where the metal is of more easy reduction, as in the case of zinc, the 

 effervescence at the negative is diminished, although it does not cease, and metal 

 separates there, apparently in consequence of a part of the hydrogen combining 

 with the electro-negative constituent of the haloid salt. 



When absolute alcohol, holding in solution chloride of magnesium, prepared 

 by Liebig's process, is acted on in a close tube, magnesia separates, after a few 

 hours' action, as a transparent and colourless crystalline layer, covering the nega- 

 tive platinum-foil, and much resembling the native hydrate of magnesia.* 



I formerly stated the changes produced by voltaic agency on alcohol, con- 

 taining very small quantities of potash in solution ; I shall now shew the action 

 on a strong solution. 



Rather more than an ounce measure of a saturated solution of hydrate of 

 potash in alcohol was submitted to the action of thirty-six pairs of 4-inch plates, 

 by parallel platinum-foil poles, placed at the distance of one-sixth or one-seventh 



* When this transparent substance was heated, it gave off moisture, so that it appeared either to be 

 a hydrate or an alcoate of magnesia, but the experiment had afforded too little to determine this point. 

 VOL. XIV. PART I. Q 



