152 



Profs. Liveing and Dewar. Spectra of the [Feb. 5, 



February 5, 1880. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table and thanks ordered for 

 them. 



The following Papers were read : — 



I . " On the Spectra of the Componnds of Carbon with Hy- 

 drogen and Nitrogen." By G. D. Liveing, M.A., F.R.S., 

 Professor of Chemistry, and J. Dewar, M.A., F.R.S., Jack- 

 sonian Professor, University of Cambridge. Received 

 February 2, 1880. 



In a memoir " On the Spectra of Metalloids " (" Nova Acta Reg. 

 Soc. Upsal.," ser. iii, vol. ix), Angstrom and Thalen have made a 

 carefnl analysis of the different spectra assigned to carbon. They 

 distinguish four sets of groups of shaded bands produced under dif- 

 ferent circumstances, which they define, besides the line spectrum 

 which they ascribe to carbon itself. Of these four sets of bands, two 

 sets, situated at the extremities of the spectrum, they show to be 

 produced in the combustion of cyanogen, a third to be common to all 

 the hydrocarbons, and the fourth to be produced by carbonic oxide. 

 The first two sets, the third, and the fourth sets respectively, they 

 observed to be produced also in the electric discharge between carbon 

 electrodes according as it took place in nitrogen, hydrogen, or oxygen. 

 Their observations on this subject appear to us almost con elusive. 

 Nevertheless, other observers have, since their publication, maintained 

 different opinions. 



The spectrum of hydrocarbons burning in air has been repeatedly 

 described: first by Swan in 1856, and afterwards by Attfield, Watts, 

 Morren, Pliicker, Boisbaudran and others, and has been given in 

 detail by Piazzi Smyth (" End on Illumination in Private Spectro- 

 scopy"). The characteristic part of this spectrum consists of four 

 groups of bands of fine lines in the orange, yellow, green, and blue 

 respectively, and we refer hereafter to these as the hydrocarbon 

 bands. These four groups, according to Pliicker and Hittorf, also 

 constitute the spectrum of the discharge of an induction coil in an 

 atmosphere of hydrogen between carbon electrodes. They are also 

 conspicuous in the electric discharge in olefiant gas at the atmo- 

 spheric and at reduced pressures. 



The descriptions of the other less conspicuous parts of the spectrum 



