1014] on Further Researches on Positive Rays 267 



other hand, when X3 is obtained by bombarding hydrogen-containing 

 substances the supply does not cease after long bombardment. 



I will now pass on to another application of the positive rays, the 

 investigation of intermediate and transient products in chemical 

 reactions. The whole process by which any particle leaves a record 

 on the photographic plate does not take more than a small fraction 

 of a millionth of a second, so that it is very suitable for the detection 

 of compounds which have a very transient existence. For example, 

 the question has been raised whether, when hydrogen and oxygen 

 combine to form water, the first stage in the process is the formation 

 of the compound H^,0o. This is not a very favourable case for the 

 method, since the molecular weight of 0^, is so near that of H/J^, 

 that there might be a danger of mistaking the parabolas due to these 

 substances. I have, therefore, tried in preference the oxidation of 

 alcohols, esters and nitrous oxide, but in none of these cases have 

 I been able to detect the existence of intermediate products. 



I have here a photograph of the positive ray spectrum of XO + 

 0^ ; it shows the known oxides of nitrogen, but I cannot find any 

 trace of NO3. It is probable, I think, that the first stages of chemical 

 combination may be condensation round nuclei, such as traces of 

 water vapour or ammonia, the whole forming a system too heavy to 

 take part in the electrical discharge, and therefore not being regis- 

 tered on the plate ; and that by the time the molecules get free from 

 the nucleus the chemical reaction has been completed. The investiga- 

 tion of this chemical embryology, as it may be called, has only just 

 been begun, and it would be premature to draw any positive con- 

 clusions at this stage of the inquiry. Another point on which we 

 may expect to get information from the positive rays is the mechanism 

 of ionisation. When a gas is ionised by cathode rays, does the 

 process involve the splitting of the molecules into atoms, or is it 

 confined to the removal of an electron from one of the atoms in a 

 molecule leaving the connection between the two atoms in the 

 molecule unbroken ? Another question which arises is, what is the 

 difference between the process of ionisation by cathode rays and that 

 of positive rays ? In the positive ray photographs we find positively 

 charged atoms and positively charged molecules of most of the 

 elements, and the alterations in the proportion of atcms to molecules 

 may throw some light on the nature of ionisation. To test whether 

 the cathode rays could split the molecules up into atoms, I tried the 

 following experiment : — I had in the discharge tube a subsidiary 

 Wehnelt cathode from which a large number of electrons were ejected 

 when it was raised to a red heat, while none were ejected when it 

 was cold, and I took positive ray photographs (1) when the Wehnelt 

 cathode was hot, and (2) when it was cold. If the cathode rays did 

 not split the molecules up into atoms, the effect of heating the 

 Wehnelt cathode would be to increase the intensity of the lines due 

 to the molecules compared with that of the lines due to the atoms. 



