RESEARCHES UPON THE CHEMICAL PROPERTIES OF GASES. 171 



to a sesquioxide at a red heat. Rhodium is convertible into a monoxide. In the 

 case of the majority of these metals, the tendency to form an unstable oxide, which 

 readily gives up its oxygen, explains the oxidizing power upon hydrocarbons. When 

 it is considered however that platinum, which iuduces oxidation nearly as readily as 

 palladium, does not produce directly an oxide when heated in air, the oxidizing 

 power possessed in common by these metals seems to require further explanation. 



10. At a bright red heat and in excess of air, palladium asbestos causes oxida- 

 tion of all hydrocarbons as efficiently as does ignited oxide of copper. 



11. Glowing of the palladium is by no means essential to slow oxidation where 

 a mere carbon dioxide reaction for the recognition of the hydrocarbon gas or vapor 

 is to be attained (that is, when a quantitative combustion is not aimed at). 



12. The proportion of finely divided metal used upon asbestos seems to be im- 

 material. Palladium asbestos containing 2 per cent, of palladium is nearly as effi- 

 cient as that containing 30 per cent. As it is difficult to distribute the metal 

 uniformly on the asbestos fibre, the higher percentage, b}^ collecting irregularly, is 

 more liable to cause glowing. Berliner (^Ann. Phys. Chem., n. F., 35, p. 791) states 

 that the catalytic action of each metal, in the case of the reaction 



112 + = HjO, 



begins at a fixed temperature and increases with rise of temperature. The oxidation 

 temperature for platinum foil is about 270° ; for copper, 280° ; for zinc, 350° ; while 

 aluminium has no action at 440'. At constant temperatures the quantity of water 

 formed is constant. My experiments do not confirm these statements. 



Krause and Meyer (Ber., 1891, p. 698, E.) state that in the presence of mercury 

 hydrogen begins to oxidize at 305°, while increasing temperature accelerates the 

 oxidation. In contact with glass alone, hydrogen burns between the limits 650° 

 and 730°. 



MIXTURES OF HYDROGEN WITH AIR AND HYDROCARBONS. 



A great number of experiments have been undertaken to ascertain the influence 

 of hydrogen upon the oxidation of hydrocarbons in presence of metals. Of these 

 the following is a summary: In a mixture of methane and air, a small proportion of 

 hydrogen does not influence the oxidation of the methane provided the rate of flow 

 of the gas mixture over the palladium asbestos is very slow. Water will form 

 readily, but no carbon dioxide, unless the temperature rises to about the melting 

 point of cadmium iodide (400°), that is to say, the temperature at which the methane 

 would be oxidized if no hydrogen were present. If the gas mixture flows rapidly, 



