STATES OF THE GASES. 51 



While this action commences below 400, it takes place slowly, and it is 

 chiefly at higher temperatures that it becomes of quantitative importance. 

 As in the case of hydrogen and water-vapor, this reaction is reversible, 

 the direction in which it will proceed depending upon the proportions of 

 the substances present. Either metallic iron or ferric oxide, heated in a 

 mixture of equal parts of carbon monoxide and carbon dioxide, produces 

 ferrous oxide. 1 Siderite at red heat passes into a magnetic oxide with the 

 formation of both carbonic acid and carbonic oxide. According to 

 Dobereiner this reaction takes place as follows: 2 



5FeCO 3 = 3FeO.Fe 2 3 + 4CO 2 + CO 



Glasson, 2 however, says that 4FeO.Fe 2 O 3 results, at first giving two parts 

 of CO 2 and one of CO, but that later the proportion changes to five parts 

 of CO 2 and one of CO. 



It is, therefore, the normal thing for a rock containing carbon dioxide 

 (whether occluded, or in cavities, or a carbonate) and iron in the ferrous 

 condition to generate carbon monoxide on the application of heat. In 

 this connection it may be noted that carbon monoxide rises very conspic- 

 uously in relative importance whenever there is metallic iron present in 

 the material tested. The iron-bearing basalt of Ovifak, Greenland, gave 

 21.63 per cent of this gas compared with 46.50 per cent of the dioxide; 3 

 the Allegan meteorite, 38.61 per cent of CO and 41.74 per cent of CO 2 ; 4 

 while the Estacado meteorite developed 29.31 per cent monoxide and only 

 28.47 per cent dioxide. 5 These were specimens of stony material contain- 

 ing grains of metallic iron. Quite different is the Toluca iron meteorite, 

 whose nearly pure metal evolved 71.05 per cent carbonic oxide with but 

 6.40 per cent carbonic anhydride. 6 Wright's figures for iron meteorites 

 are equally noted for high percentages of carbon monoxide. 7 



However, there are two other chemical sources for carbon monoxide, 

 one of which is, perhaps, especially applicable to iron meteorites. It is 

 known that the carbides of chromium and iron, when heated with the 

 oxides of these metals, produce carbonic oxide. 8 As these meteorites often 

 contain considerable carbon, some of it perhaps as a carbide, scrupulous 

 care is always necessary in preparing the metal for the analysis, to avoid 

 introducing any rust from the oxidized exterior of the mass. 



The other principle must always be operative in the combustion-tube. 

 Boudouard has shown that at the temperatures of the combustion-furnace 

 hydrogen reduces carbon dioxide, forming carbon monoxide at the expense 

 of both hydrogen and the dioxide. 3 



1 Wright and Luff, Jour. Chem. Soc., vol. 33 (1878), p. 504. 



2 Cited by Gmelin-Kraut, Anorg. Chem., vol. 3, p. 319. 



3 Analysis No. 45. 



4 Analysis No. 106. 



5 Analysis No. 107. 

 8 Analysis No. 108. 



7 See p. 6. 



8 Borchers and McMillan, Electric Smelting and Refining, p. 545. 



9 O. Boudouard, Chem. Central-Blatt (1901), 1, p. 1350. 



