Mr. Grove on the Decomposition of Water by Heat. 21 



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 ehdosmose, which takes place 

 through all porcelain vessels. I therefore determined to 

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

 verifying, under different circumstances, known results, and 

 seeking for new effects by this new and advantageous appli- 

 cation. I used an eudiometer (fig. 1) of 8 inches long and 

 0'4' inch internal diameter, exposing the gases to intense heat, 

 and subsequently 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 incandescence 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 best shown by including a volta- 

 meter in the circuit. Davy found that the conducting power of 

 a wire diminished in proportion to the degree to which it was 

 heated : assuming the accuracy of this position, the amount of 

 gas in the voltameter would be inverse to the intensity of ig- 

 nition in the wire. The following is the result I obtained with 

 different gases, employing the same battery (the nitric-acid 

 combination at its most constant period), the same wire, and 

 the same vessel : — 



Cubic inches of gas evolved in 

 Gases surrounding the wire. the voltameter, per minute. 



Hydrogen ....... 7*7 



defiant gas 7*0 



Carbonic oxide ...... Q'Q 



Carbonic acid 6'6 



Oxygen 6'5 



Compressed air, 2 atmospheres 6'5 



Nitrogen 6'4 



Atmospheric air 6*4 



Rarefied air Q'3 



Chlorine 6-1 



* Phil. Mag. Dec. 1845. 



