130 CONSTRUCTION OF GAtV.ANIC BATTERIES. 



is certain, that it may be rolled much thiner than is requir- 

 ed for this purpose, in its pure state*. 



I am, Sir, 



Your obedient servant, 

 Jan. 2<*, I809. G. K. M. 



REPLY. 

 Having taken the liberty of troubling Mr. Davy with a 

 line on the subject here stated, I was favoured with his an- 

 swer, from which I extract the following. 

 Battery capa* M In my early experiments upon potassium, I often pro- 



bleof decom- Cure( j ft by means of a battery of one thousand pairs of 

 posing potash. . *■ 



plates of copper and zinc of six inches square, charged with 



a solution of concentrated nitrous acid in about forty parts 

 of water. This is the lowest power that I employed : but 

 as some of the plates had been much corroded by former 

 processes, I should conceive, that a combination of eighty 

 would be sufficient, provided the whole arrangement was 

 perfect. 

 Less power " The decomposition of the alkaline earths and ammonia 



sufficient for by amalgamation or combination of their bases may be ac- 

 ammonia! complished by a much weaker combination, fifty plates of 

 six or four inches square being adequate to produce sensi- 

 ble results. 

 Potassium may " The potassium, which I have used in various analytical 



be procured enquiries lately carried on, has been ail procured by chemi- 

 withoutelec- * .. ,',..«,■•,,■ 



tricity. cal means, without the application or electricity. 



" Potash may be decomposed by different processes, some 

 of which are described in a paper, which I am now reading 

 before the Royal Society; but the best method is that, 

 which we owe to the ingenious researches of Messrs. Gay 

 Lussac and Thenard, and which is the first of this kind, by 

 mere chemical attraction, made known. 

 Chemical de- « When melted potash is slowly brought into contact with 

 of 3ush° n * ron tunun g s > or filings heated to whiteness, hidrogen gas is 

 evolved, holding potassium in solution • and if one part of 

 the iron tube, or gun barrel, in which the experiment is 

 made, be preserved cool, the metal is deposited in this part, 

 being precipitated from the hidrogen gas by cooling. 

 • And at the common temperature. 1$. 



« The 

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