172 



RESEARCHES UPOIST THE CHEMICAL PROPERTIES OP GASES. 



the burning hydrogen may so intensely heat the palladium as to cause it to glow. 

 This involves an immediate production of carbon dioxide. With a slow movement 

 of the gas, considerable volumes of hydrogen may be burned without formation of a 

 trace of carbon dioxide. This is the conclusion reached by Hempel ; but I have 

 found the temperature at which the hydrocarbon is oxidized to be much higher than 

 he supposes (about 200°). The same statement is true of hydrogen and ethane, 

 and in general it may be said that the paraffins in presence of hydrogen and excess 

 of air only undergo oxidation by palladium asbestos when the too rapid oxidation of 

 the hydrogen causes glowing of the palladium. 



The same general phenomena are observed in the case of mixtures of olefines 

 and hydrogen with air. The temperatures of oxidation of the olefines are always 

 lower than those of the corresponding paraffins. Below the temperature needed for 

 oxidation a contraction in volume often occurs, due probably to occlusion by palla- 

 dium. The addition of hydrogen to a mixture of air and carbon monoxide lowers 

 the temperature of oxidation of the carbon monoxide by palladium asbestos. While 

 the carbon monoxide alone in air was oxidized at temperatures above 300°, in presence 

 of hydrogen it may yield CO2 below 100°. 



As has already been stated, the slow oxidation by palladium of a hydrocarbon 

 in excess of air involves the conversion of carbon into carbon dioxide only, no carbon 

 monoxide being produced. Experiments were made with a gaseous mixture having 

 the following composition : 



Propane 3.1 



Hydrogen , 2. 



Air 94 9 



Oxidation of the paraffin occurred at temperatures varying from 270° to the melting 

 point of potassium nitrate (339°), but in no case was any carbon monoxide produced 

 nor could any olefines be detected, in the gas after passing the palladium, 



ACTION OF HTDKOCARBOISrS UPON METALLIC OXIDES. 



As the temperature of oxidation by air in presence of finely divided metals 

 seemed to vary within rathei' wide limits, it was possible that the differences might 

 be due to a lack of absolutely uniform conditions in the various trials. So much 

 care had been taken as regards the temperature and preparation of metal-coated 

 asbestos that there was no positive ground for supposing that the apparatus and 

 materials employed were in any way at fault. 



To still fuither study the matter, a series of trials was made of the temperature 

 of reaction between reducing gases and the following compounds : Oxide of copper, 



