376 Prof. J. Trowbridge on the Spectra of 



with copper terminals and rendered luminous by condenser- 

 discharges : — 



Cyanogen, 



Carbon monoxide, 



Carbon dioxide, 



Acetylene. 



Cyanogen was prepared by heating mercuric cyanide, and 

 passing the gas over sulphur to remove any traces of mercury- 

 vapour. Carbon monoxide was prepared by heating potassium 

 oxalate with concentrated sulphuric acid, and passing the gas 

 over potassium hydroxide, and collecting over water. Carbon 

 dioxide was prepared by treating potassium carbonate with 

 dilute sulphuric acid and collecting over water. All of these 

 gases were allowed to remain in contact with phosphoric 

 pentoxide before introduction into the tubes. 



With acetylene, carbon monoxide, and carbon dioxide, 

 condenser-discharges being employed, the results appear to 

 be identical with those obtained with hydrogen in the tube 

 with carbon electrodes. With cyanogen, the same lines 

 appear ; and, in addition, the bands which are characteristic 

 of these gases with continuous currents, which will be described 

 later. In general, with condenser-discharges, all these spectra 

 are the same ; the differences which occasionally appear 

 may be due to changes in pressure, time of exposure, &c. 



The line 4268, in all these cases, is by far the most promi- 

 nent line present in the region studied ; and may be taken as 

 characteristic of hydrogen, oxygen, and nitrogen in tubes 

 with carbon terminals, and of gaseous carbon compounds in 

 tubes with metallic terminals. This line does not usually 

 appear in hydrogen in tubes with metallic terminals ; occa- 

 sionally it appears very faintly. It appears, however, very 

 strongly in a tube provided with platinum terminals which is 

 filled with hydrogen and heated for two hours during ex- 

 haustion to a temperature of 350° C. The spectrum, in this 

 case, appears to be identical with the spectrum of hydrogen 

 in a tube provided with carbon terminals. Were it not for 

 this fact, it would seem as if this line were due to carbon in 

 some form ; but even with this fact, it is possible that there 

 was enough foreign carbonaceous matter present in the 

 platinum tube to produce the result noted. 



Eder & Yalenta * find, among others, the following lines in 

 the spectrum of an induction-coil between carbon terminals: 



4268 



3921 



* Beiblatter, xviii. 1894, p. 753. 



