284 EXPERIMENTAL INVESTIGATIONS. 



bubble ; this was probably nitrogen from the atmospheric air 

 in solution, which had escaped to fill the vacuum. When the 

 stopper was taken out the liquid rose suddenly in the hydro- 

 gen tube 2'2 cubic inches, giving the equivalent of the oxygen 

 in the tube and in solution. It is very possible that this ex- 

 periment repeated might sometimes exhibit an evolution of 

 hydrogen in the oxygen tube arising from the escape of the 

 nitrogen of the atmospheric air in solution, and acting as in 

 Experiment 29, but I have not seen this effect take place. It 

 should be distinctly understood that in all the experiments 

 mentioned in this postscript, except the first part of Experi- 

 ment 28, single cells only were used. 



Upon the theory of the Experiments 29 and 30 I will 

 venture no positive opinion. That gaseous hydrogen should 

 abstract oxygen from hydrogen, without the latter forming any 

 other combination, is a fact so novel, that any attempted ex- 

 planation is likely to prove premature. If, contrary to the 

 views of Dalton, we suppose that gases when mixed are held 

 together by a feeble chemical affinity, then we may say that 

 the affinity of the nitrogen or carbonic acid for hydrogen pro- 

 duces the effect ; the affinity of the oxygen of the water, 

 being balanced between the hydrogen in the liquid and that 

 in the tube, would enable the resultant feeble affinity of the 

 nitrogen for hydrogen to prevail ; but on this supposition why 

 does not oxygen produce an analogous effect ? Its tendency 

 directly to combine with platinum may indeed be regarded as 

 an opposing force, but this tendency is by many considered 

 hypothetical. On the other hand, it may be called an effect 

 of contact ; but this, unconnected with a chemical theory, 

 presents no other idea to the mind than the fact itself pre- 

 sents- it furnishes no link by which we may extend the phe- 

 nomena. I therefore, until a better theory be found, should 

 be inclined to adopt the former view, and to regard mixed 

 gas as in a state of feeble chemical union, the more especially 

 as throughout nature we find no absolute lines of demarcation, 

 though for conventional reasons we arc obliged to adopt them. 

 There must be many cases in which it is difficult, if not im- 

 possible, to draw the line between mechanical mixture and 

 chemical combination. 



