2 
MR. GROVE ON THE DECOMPOSITION OF WATER BY HEAT. 
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 igni- 
tion ; in that experiment the vapour of camphor was decomposed into carbonic oxide 
and carburetted hydrogen ; it was an application 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 indefinitely small ; that there are no joints, stop-cocks or ligatures ; and that 
there is no chance of endosmose, w T hich 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 application. I used an eudiometer (fig. 1) of 8 inches 
long and 0‘4 inch internal diameter, 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 men- 
tioned 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 atmo- 
spheric 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 voltameter 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 ignition 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. 
Hyd rogen 7*7 
Olefiant gas 7*0 
Carbonic oxide 66 
Carbonic acid 6‘6 
Oxygen .......... 65 
Compressed air, 2 atmospheres . . 65 
Nitrogen 6*4 
Atmospheric air 64 
Rarefied air 63 
Chlorine 6T 
* Philosophical Magazine, December 1845. 
