426 EXPERIMENTAL INVESTIGATIONS, 



I tried also phosphorus highly heated by a burning-glass 

 in an atmosphere of nitrogen, but could eliminate no percep- 

 tible quantity of gas, though the phosphorus was changed 

 into the allotropic form. 



It is not difficult to understand why gas is not perceptibly 

 eliminated in the last two experiments ; the effect is probably 

 similar to that described in my paper on ' The Decomposition 

 of Water by Heat/ where, when the arc or electric spark is 

 taken in aqueous vapour, a minute bubble of oxyhydrogen 

 gas is freed and disseminated through the vapour, recombina- 

 tion being probably prevented by this dilution ; but, however 

 long the experiment may be continued, no increased quantity 

 of the gas is obtained, all beyond this minute quantity being 

 recombined. If, however, the bubble of gas be collected, by 

 allowing the vapour to cool, and then expelled, a fresh portion 

 is decomposed, and so on. 



So with the phosphorus in the experiments in the air-pump 

 and with the burning-glass, if any gas is liberated it is probably 

 immediately recombined with the phosphorus ; possibly a 

 minute residuum might escape recombination, but the circum- 

 stances of the experiment did not admit of this being collected, 

 as was the case with the gas in aqueous vapour. 



When, on the other hand, the gas freed is immediately cut 

 off from the source of heat, as when the spark is taken in 

 liquids, an indefinite quantity can be obtained. 



Decomposition and the elimination of gas may thus take 

 place by the application of intense heat to a point in a liquid, 

 or also in gas or vapours, but in the latter case it is more likely 

 to be masked by the quantity of gas or vapour through which 

 it is disseminated. 



I believe there are very few gases in which some alteration 

 does not take place by the application of the intense heat of 

 the voltaic arc or electric spark. If the arc be taken between 

 platinum points in dry oxygen-gas over mercury, the gas 

 diminishes indefinitely, until the mercury rises, and by reaching 

 the point where the arc takes place puts an end to the expe- 

 riment. I have caused as much as a cubic inch of oxygen to 

 disappear by this means. I at one time thought this was due 

 to the oxidation of the platinum, but the high heat renders 



