572 



MR. 11. HHKHKTO.N I'-AKKU OX I'OilliUSTlON IN DRIED OXYGEN. 



previously introduced, the two substances being separated by a disc of platinum foil. 

 The latter did not fit so closely as to prevent the free diffusion of the gaseous contents 

 of the tubes. Oxygen dried by sulphuric acid was then passed through the tubes, 

 which were then sealed at both ends. Experiments have shown that the long contact 

 of phosphorus pentoxide with gases has an immeasurably greater drying effect than 

 the mere passage of the gases through tubes containing that substance. After 

 standing for some days each of these tubes was heated, side by side with a similar 

 tubs containing charcoal in moist oxygen, by the flame of a large Bunsen burner. 

 The moist carbon always burnt with the scintillation characteristic of such a combus- 

 tion, but the dry carbon remained apparently unaltered. On analysis, however, it 

 was found that a certain quantity of carbon had been burnt. The following Table 

 gives the results of the analysis of the gaseous contents of the tubes, after the carbon 

 had been heated to redness in them for about two minutes. 



It will be noticed that in four out of these six experiments more than half the 

 oxygen was left uncombined with the carbon, whilst none remained in the wet tubes. 

 The comparatively large quantities of carbon monoxide produced are striking when we 

 consider that the temperature was not high, and that the reduction of carbon dioxide 

 by carbon is never rapid. These results formed the starting point of an investigation 

 in which the precautions taken to ensure the purity and dryness of the substances 

 used were made much more elaborate. 



The carbon used in the later experiments was in the form of charcoal. It was 

 prepared by heating sugar in a silver dish to a bright red heat. The porous mass was 

 broken up and finely powdered. It was transferred to a combustion tube, and heated 

 to redness for three days in a current of pure chlorine dried by sulphuric acid, in 

 order to eliminate hydrogen from the powder. The charcoal was washed by decanta- 

 tion with distilled water until the washings gave no opalescence with silver nitrate. 

 To free it from occluded hydrochloric acid, it was placed in a hard glass tube sealed at 

 one end, while at the other end was placed a stick of solid potash. The tube was 

 then exhausted by a Sprengel pump, and the end containing the carbon was heated 

 to dull redness for several days, the vacuum being constantly maintained. Hydro- 

 chloric acid gas was evolved, partly absorbed by the potash, but at first passing over 

 in such quantities that it could be collected from the air-pump. After this treatment 



