Spectra of Carbon Compounds. 489 



filled at a moderate pressure, and then exhausted until the 

 discharge passed. The spectrum was examined first with the 

 ordinary discharge and then with a leyden-jar and spark-gap 

 in the circuit. 



Stages of Ordinary discharge. Condensed discharge. 



Exhaustion. (Jar and air-gap.) 



1. Swan spectrum. No discharge. 



2. Swan and faint oxycarbon. Swan spectrum. 



3. Swan and weak oxycarbon. Swan and carbon line 



and oxygen line. 



4. Swan and oxycarbon } Carbon line and oxygen 



equally. line. With a short 



gap the oxycarbon 



5. Swan weakening, oxycar- K r is seen also ; with a 



bon strengthening. longer gap "the Swan 



(faiut) displaces the 



6. Oxycarbon only. j oxycarbon. 



Later stages. The oxycarbon fades, the No discharge, 



mercury spectrum grows 

 in intensity, then fades 

 until there is complete 

 fluorescence in the tube. 



The experiment was repeated in the reverse order, that is 

 to say, beginning with an exhausted tube and allowing carbon 

 monoxide to enter in small instalments. The results were 

 exactly the same. 



The " stages of exhaustion " used above do not represent 

 equal decrements of pressure, but are chosen to show the main 

 features of change undergone by the spectrum. 



The results above described agree perfectly with the 

 observations of Liveing and Dewar (loc. cit.). 



According to the experiments of Tietz (Spectrum des 

 Koldenstoffs. Inaug. Dissert. Berlin, Buxenstein, 1894) the 

 spectrum of carbon monoxide subjected to the condensed 

 spark-discharge between platinum electrodes at ordinary 

 atmospheric pressure contains only the lines of oxygen and 

 carbon (line spectrum). 



Carbon Dioxide. 



The spectrum of carbon dioxide was mapped in detail by 

 Angstrom & Thalen (loc. cit.). The variations which the 

 spectrum undergoes with changes in pressure, changes in the 

 character of the discharge, and with changes in the length of 

 the containing tubes, were described at great length by 



Phil. Mag. S. 6. Vol. 1. No. 4. April 1901. 2 K 



