418 



Profs. G. D. Liveing and J. Dewar. [Dec. 21,. 



spoken of be held in the smoke-box in a vertical instead of in a 

 horizontal plane, the lines of motion are mnch less curved, and we 

 might expect to eliminate the influence of centrifugal force. I have 

 not succeeded in this way in getting rid of the dark plane ; but since 

 under the magnifier the curvature of the motion was still quite 

 apparent, no absolute conclusion can be drawn. 



Y. " On the Origin of the Hydrocarbon Flame Spectrum." By 

 G. D. Liveing, M.A., F.R.S., Professor of Chemistry, and 

 J. Dewar, M.A., F.R.S., Jacksonian Professor, University 

 of Cambridge. Received December 14, 1882. 



In previous communications* to the Society we have described the 

 spectra of what we believe to be three compound substances, viz.,. 

 cyanogen, magnesium-hydrogen, and water. 



In these investigations our chief aim has been to ascertain facts, 

 and to avoid as far as possible adopting any special theory regarding 

 the genesis of the spectra in question. Thus, in speaking of the 

 magnesium-hydrogen spectrum, which consists of three sets of 

 flutings closely resembling in character the flame spectrum of hydro- 

 carbons, we remark : — " We have been careful to ascribe this line 

 and its attendant series to a mixture of magnesium and hydrogen 

 rather than to a chemical compound, because this expresses the facts, 

 and we have not yet obtained any independent evidence of the ex- 

 istence of any chemical compound of those elements." 



In dealing with the cyanogen spectrum, we sometimes refer to it as 

 the " nitro-carbon spectrum," in order to convey that "we are 

 dealing with a spectrum invariably associated with the presence of 

 nitrogen and carbon, in such conditions that chemical union takes 

 place." Finally, in summing up our observations on the spectrum of 

 water, we remark : — " In writing of this and other spectra which we 

 have traced to be due to compounds, we abstain from speculating 

 upon the particular molecular condition or stage of combination or 

 decomposition which may give rise to such spectra." 



The difficulties we have met with in endeavouring exhaustively to 

 clear up many apparently simple spectroscopic problems, on a basis of 

 fact as opposed to theory, is further illustrated in the concluding 

 remarks of our paper entitled " Investigations on the Spectrum of 



* " On the Spectra of the Compounds of Carbon with Hydrogen and Nitrogen." 

 I and II. " Proc. Koy. Soe.," vol. 30, pp. 152, 494. " On the Spectrum of 

 Carbon," ib., vol. 33, p. 403. " General Observations on the Spectrum of Carbon 

 and its Compounds," ib., vol. 34, p. 123. " On the Spectrum of Water," ib., vol. 30, 

 p. 580, and vol. 33, p. 274. " Investigations on the Spectrum of Magnesium," ib., 

 vol. 32, p. 189. 



