4,88 



Prof. A. Smithells on th 



ie" 



speaking, it may be said that four distinctive spectroscopic 

 features have been noticed in connexion with these gases. 

 Under different circumstances there may be obtained (i.) the 

 Swan spectrum, (ii.) the oxycarbon-spectrum, (iii.) the 

 carbon line- spectrum. The fourth feature is (iv.) in connexion 

 with carbon dioxide a band in the red which, according to 

 Piiicker (Pogg. Ann. cv. p. 77, 1858), disappears on sparking. 

 I have reinvestigated the spectra of the oxides of carbon 

 and shall now describe the results. I will, however, preface 

 the account by repeating that I have never been able to 

 verify the observation of Piiicker above referred to, and that 

 I recognize therefore only three spectra as obtainable from 

 the oxides of carbon. It is worth remarking that the appear- 

 ance to the naked eye of the discharge through the oxides of 

 carbon affords an indication of which of the three spectra is 

 predominant. Thus the Swan spectrum is associated with a 

 greenish blue light very like that of the inner cone of a 

 Bunsen flame burning with much air ; the oxycarbon 

 spectrum is seen when the discharge is a pale blue or white ; 

 whilst the carbon line-spectrum is associated with a pinkish 

 discharge. 



Carbon Monoxide. 



The gas was prepared by the action of strong sulphuric 

 acid on recrystallized lead formate. It was allowed to rest 

 in contact with solid potassium hydrate, and afterwards with 

 phosphoric oxide. The Toepler pump, to which the Piiicker 

 tube was sealed, was provided with arrangements whereby the 

 pressure of the gas could be increased or diminished in 

 regular stages between the limits of one atmosphere and a 

 high vacuum. The discharge was effected by means of an 

 induction-coil capable of giving a six-inch spark in air. A 

 ley den-jar and a spark-gap could be introduced at will. A 

 Steinheil spectroscope with two flint-glass prisms was used 

 to observe the spectra. No attempts were made to improve 

 upon existing maps of the spectra concerned — the object 

 being rather to observe the conditions under which one or 

 other of the spectra appeared. A comparison prism bringing 

 into the field of view the bright Swan spectrum of a well- 

 aerated Bunsen flame was generally used. 



The least refrangible line (516*4) of the group in the green 

 is an excellent datum-line, since close on one side of it lies 

 the edge of an oxycarbon band (519*7), and on the other a 

 line of the carbon line-spectrum (515*05). 



The behaviour of carbon monoxide may perhaps be most 

 clearly described by means of a table. The Piiicker tube was 



