Spectra of Carbon Compounds. 497 



spectrum is often to be distinctly seen under the circumstances 

 described above, but I have also found that this ceases to be 

 the case as the hydrogen is more and more thoroughly 

 purified. 



Carbon points were prepared from gas-carbon and were 

 heated for two hours with concentrated nitric acid, then with 

 hydrofluoric acid. They were then washed with distilled 

 water and heated to bright redness about an hour and a half 

 in a platinum tube through which a current of dried hydrogen 

 was passed. The object of this treatment was to remove as 

 far as possible any compound containing oxygen. 



Hydrogen was prepared by the electrolysis of dilute sodium 

 hydrate solution and dried by means of solid potash and 

 phosphoric oxide. In the earlier experiments sodium amalgam 

 was introduced into a side chamber of the sparking tube, and 

 after the discharge had passed some time the amalgam was 

 boiled. Though the results obtained in this case were pro- 

 mising the method was abandoned owing to the numerous 

 fractures that occurred. In all subsequent experiments the 

 hydrogen was prepared either by electrolysis of dilute sodium 

 hydrate solution or by the action of dilute hydrochloric acid 

 on distilled zinc, a drop or two of platinum chloride being 

 added to induce the action. The gas was passed over solid 

 potash and then led into a short eudiometer standing in 

 mercury and containing a slick of solid potassium hydrate. 

 The gas was there sparked for one or tw T o hours in order that 

 any lingering traces of oxygen should be converted into 

 water. It was then allowed to pass directly into the carbon 

 electrode tube sealed to the Toepler pump and connected with 

 phosphoric oxide tubes. The pump and tube exhausted to 

 the highest obtainable degree to begin with were repeatedly 

 filled w T ith the purified hydrogen and re-exhausted. As this 

 process was continued the discharge was from time to time 

 allowed to pass between the carbon electrodes and the spectrum 

 noted . Without describing in detail the numerous experiments 

 made on this plan I may summarize the results as follows : — 



In all stages of purification the discharge between the 

 carbon poles was bright red when a jar and gap were em- 

 ployed in the circuit, and the simple line-spectrum of hydrogen 

 was very bright. With the uncondensed discharge the colour 

 was white and the compound line spectrum of hydrogen ap- 

 peared. In the earlier stages of purification these hydrogen 

 spectra were accompanied to a greater or less extent by the 

 Swan spectrum, and the red or white discharge was seen to 

 be surrounded by the greenish aureole which, as already 

 remarked, is always associated with the Swan spectrum. 



