170 RESEARCHES UPON THE CHEMICAL PROPERTIES OF GASES. 



or even more degrees, a sudden intense reaction occurs in the lime water, suggesting 

 the change from smouldering fire to actual flame. Very often this slow oxidation 

 is not observed and the carbon dioxide reaction occurs in the lime water suddenly 

 and with full intensity. The hydrocarbon molecule seems to exist at high tempera- 

 tures in a condition of unstable equilibrium towards oxygen. In the preceding 

 statements the temperatures given are those of decided and intense reaction in the 

 lime water. 



3. The oxidation of a hydrocarbon by air, under conditions similar in all re- 

 spects, does not occur always at the same temperature. It may vary within rather 

 wide limits of the thermometer scale. A variation in the proportion of hydrocarbon 

 and air does not seem to materially influence the oxidation temperature. 



4. The paraffins are the most stable towards heated air in presence of palladium. 

 Acetylene and carbonic oxide stand next in order. The olefines are the most easily 

 oxidized. 



5. Of the members of the same homologous series of hydrocarbons, the lower 

 are the more stable towards oxidizing influences. 



6. Hydrogen stands alone among combustible gases in undergoing oxidation 

 under the influence of palladium-coated asbestos in the cold. 



7. Oxidation of gaseous hydrocarbon in excess of air involves the simultaneous 

 formation of CO2 and H2O. 



8. In all cases where air is in excess, oxidation is complete (^. e., yielding only 

 CO2 and HjO), even though a considerable portion of the hydrocarbon may escape 

 unchanged. With insufficient air supply, CO, may be partly replaced by CO among 

 the products of oxidation. 



9. As regards oxidizing power, the metals which I have studied might be 

 arranged in the following order, beginning with the most active: (1) Osmium, 

 (2) palladium, (8) platinum, ruthenium, (4) iridum, (5) rhodium, (6) gold. 



Osmium is decidedly the most powerful, causing oxidation of ethylene even 

 below 150°. Rhodium is less efficient as regards oxidation of hydrogen than palla- 

 dium. Oxidizing power is apparently not dependent upon atomic weight. Of these 

 metals, osmium in fine division is the most easily converted into an oxide. Heated 

 in a flame it burns, exhibiting much the appearance of burning lamp-black, and 

 yields, as is well known, the volatile osmium tetroxide. At much lower temperatures 

 the metal is slowly oxidized and volatilized. Palladium in fine division is converted 

 into a stable oxide, Pd^O, on heating to redness (Wilm, Bev.^ 1892, p. 220). Plat- 

 inum and gold are not oxidizable in air at any temperature. Ruthenium oxidizes 



