DECOMPOSITION OF WATER BY HEAT. 307 



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 a g e 358, I have shown another 

 method of eudiometry also performed by voltaic ignition ; in 

 that experiment the vapour of camphor was decomposed into 

 carbonic oxide and carburetted hydrogen ; it was an appli- 

 cation of voltaic ignition to effects analogous to those produced 

 by Priestley and others, by passing compound gases through 

 ignited tubes of porcelain. 



But the voltaic process has this immense advantage, that 

 the heat can be rendered incomparably more intense ; that 

 the quantity of vapour or gas to be operated on may be inde- 

 finitely small ; that there are no joints, stop-cocks or ligatures ; 

 and that there is no chance of endosmose, which takes place 

 through all porcelain vessels. I therefore determined to ex- 

 amine by these means several gases, both with a view of 

 verifying, under different circumstances, known re- Fig. i. 

 suits, and seeking for new effects by this new and 

 advantageous application. I used an eudiometer 

 (fig. i) of 8 inches long and 0*4 inch internal dia- 

 meter, exposing the gases to intense heat, and subse- 

 quently analysed the residues in one of the same 

 length, but 0*2 inch diameter. 



I will first consider the physical effects of different 

 gases on the ignition of the wire itself. 



In a paper on the ' Application of Voltaic Ignition _ 

 to lighting Mines/ * I have mentioned the striking effects of 

 hydrogen in reducing the intensity of ignition of a platinum 

 wire, so much so that a wire voltaically ignited to incan- 

 descence in atmospheric air, is apparently extinguished by 

 inverting over it a jar of hydrogen ; with other gases the 

 effects are not so striking, and with them these differences are 



* Phil. Mag., Dec. 1845. 



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