496 



Prof. A. Smithells on the 



quite apart from the purely chemical difficulties in obtaining 

 pure materials. 



Hasselberg has observed (Mem. tie I' Acad, de St. Peters- 

 bourg, xxxi. No. 14, p. 7, 18&3) that some kinds of glass 

 persistently give rise to carbon and oxygen, contamination 

 bringing to light the oxycarbon spectrum. 



Professors Liveing and Dewar state that " no chemist who 

 remembers the extreme sensibility of the spectroscopic test, 

 and the difficulty, reaching almost to impossibility, of re- 

 moving from apparatus and material the last traces of air 

 and moisture, will feel any surprise at the presence of small 

 quantities of either hydrogen or nitrogen in any of the gases 

 experimented on." 



Again they say " Photographs of the ultra-violet spectra 

 given by such tubes tell tales of impurities as unexpected as 

 they are difficult to avoid. Every tube of hydrogen which 

 we have examined exhibits the water spectrum more or less, 

 even if metallic sodium has been heated in the tube or the 

 gas dried by prolonged contact with phosphorus pentoxide. 

 We have expended a vast amount of time and trouble over 

 vacuous tubes, and our later experiments do but confirm the 

 opinion which we had previously formed that there is an un- 

 certainty about them, their contents and condition which 

 makes us distrustful of conclusions which depend on them.''' 



The difficulty of obtaining carbon tetrachloride free from 

 oxygen has been shown by Mr. Brereton Baker (Journ. 

 Chem. Soc. lxi. p. 728, 1892), whilst both he and Prof. J. 

 J. Thomson (Journ. Chem. Soc. lxv. p. 611 ; Phil. Mag. Oct. 

 1893) have shown to what an important extent the passage 

 of the electric discharge through gases is determined by the 

 presence of a trace of moisture. 



Notwithstanding the authority of these observations and 

 the small promise they afforded of a determinate result being 

 obtained, 1 have expended a great deal of time in examining 

 the spectra mentioned above, and I now record the results. 



The Spectrum of the Discharge between Carbon Electrodes 

 in an Atmosphere of Hydrogen. 



Angstrom and Thalen, in the paper already referred to, 

 state that the aureole of the spark-discharge taken between 

 carbon points in an atmosphere of hydrogen exhibits the Swan 

 spectrum, and they regarded this as a strong confirmation of 

 their view that the Swan spectrum was due to acetylene. 

 No account is given in their paper of the precautions taken 

 to purify the hydrogen. 



In repeating this experiment I have found that the Swan 



