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IV. On certain Phenomena of Voltaic Ignition and the De- 

 composition of Water into its constituent Gases by Heat. 

 % W. R. Grove, Esq., M.A., F.R.S.'^ 



IN the Philosophical Magazine for August 1841, I recom- 

 mended for eudiometrical purposes, the use of a platinum 

 wire ignited by a voltaic battery. In fig. 1 is re- Fig. 1. 

 presented a form of apparatus for this purpose ; it . 

 consists of a tube of Bohemian glass, vi'ith a loop of ^ 

 platinum wire |j\jth of an inch diameter sealed into 

 its upper end ; the size of the glass tube may be 

 adapted to the quantity of gas sought to be analysed, 

 and may when necessary be reduced to extremely 

 small dimensions, one-eighth of an inch being ample: 

 into this the gas may readily be made to ascend, by 

 the insertion of a wire of copper, platinum, or glass, 

 as may be suitable to the gas : two cells of the nitric- 

 acid battery are sufficient fully to ignite the wire, 

 and the same battery supplies, by electrolysis, pure 

 oxygen and hydrogen for the analysis. Since the -— '^^— 

 period when I first proposed this, I have seldom used any 

 other apparatus for such gaseous analyses as are performed 

 by combining the gas to be examined with oxygen or hydrogen. 

 This eudiometer possesses the advantage of enabling the ope- 

 rator either to detonate or slowly to combine the gases, by 

 using different powers of battery, by interposing resisting 

 wires, or by manipulation alone, — a practised hand being able 

 by changing the intervals of contact to combine or detonate 

 the gas at will. My general practice has been to produce a 

 gentle heat in the wire until the gases contract, and then gra- 

 dually to increase the heat until a full ignition takes place, by 

 which means all the objects of the eudiometer of Volta are 

 fulfilled, without detonation, without dependence on the fickle 

 electric spark, and without thick tubes, any danger of explo- 

 sion, or of the gases being projected from the eudiometer. 



I have commenced with a description of this eudiometer, 

 as it has been indirectly the means of my undertaking the 

 experiments detailed in this lecture; and as its very great 

 convenience has never been generally understood, I think that 

 in strongly recommending it, I shall be of service to chemists. 



In a paper honoured by insertion in the Philosophical 

 Transactions for 1845, p. 358, I have shown another method 

 of eudiometry also performed by voltaic ignition ; in that ex- 

 periment the vapour of camphor was decomposed into car- 

 bonic oxide and carburetted hydrogen ; it was an application 



* From the Philosophical Transactions for 1847, part i. ; having been 

 received by the Royal Society September 3, and read November 19, 1846. 



