56 THE GASES IN ROCKS. 



approximately equal volumes of hydrogen and carbon monoxide to the 

 action of electricity for five hours in an induction-tube. 1 From his results 

 he expressed this reaction by the equation, 



Though it is not safe to assume that this reaction will take place at 

 the temperatures of the combustion-furnace, the observation that marsh-gas 

 is obtained when a rock powder, exhausted of its gases, is exposed to the 

 air for a few months, and reheated, possibly points toward some reaction 

 of this nature. 



NITROGEN. 



If the nitrogen which is obtained from heating igneous rock powders 

 in vacuo is derived from some chemical compounds decomposable at red 

 heat, a metallic nitride at once suggests itself as the most probable form in 

 which the nitrogen would occur. Iron nitride may be taken as the type for 

 discussion. While different nitrides of iron, having the compositions of 

 Fe 2 N 2 , Fe 2 N, and Fe 5 N 2 , have been described by some authors, a compre- 

 hensive study, by Fowler, of this formerly little-known compound, forces 

 the conclusion that there exists 2 only one iron nitride, Fe 2 N. This com- 

 pound may be prepared by the action of ammonia either upon ferrous 

 chloride, or finely divided iron. While the action between ferrous chloride 

 and ammonia commences near the melting-point of lead (327), a tem- 

 perature of 600 appears to be necessary for the production of iron nitride 

 in quantity. 3 The nitride can also be produced at 850 to 900, but this 

 is probably the highest limit of the reaction. 4 



This nitride is very soluble in dilute acids, giving ammonia. When 

 heated to redness in hydrogen, ammonia results. At 200 it is oxidized 

 in the air to ferric oxide, abandoning nitrogen, which does not appear to 

 be oxidized. At 100 steam causes a slight evolution of ammonia. Accord- 

 ing to Fowler the temperature of decomposition of iron nitride in an inert 

 gas (nitrogen) must certainly be above 600. 



Silvestri has found iron nitride coating some of the fumarole deposits 

 of Etna, 5 and Boussingault 6 recognized nitrogen in the Lenarto meteor- 

 ite by certain tests which led him to believe that it existed there as a 

 metallic nitride. Silvestri discovered that at red heat the nitride from 

 Etna was decomposed, delivering up its nitrogen. His experiments show- 

 ing that iron nitride may be prepared artificially, by igniting the ordinary 

 lava in a current of ammonium chloride vapor, probably illustrate what 

 takes place in the fumaroles. But this nitride, which derives its nitrogen 

 from ammonia or ammonium salts, in no way requires the existence of 

 nitrides within the magma itself, except as a possible source for the nitro- 

 gen which unites with hj^drogen to form the ammonia. There is danger 

 in transferring the characteristics of fumarole deposits, which are formed 



1 Sir B. C. Brodie, Proc. Roy. Soc., vol. 21 (1873), p. 245. 



2 Fowler, Jour. Chem. Soc., vol. 79 (1901), pp. 285-299. 



3 Fowler, Chem. News, vol. 82 (1900), p. 245. 



* Beilby and Henderson, Jour. Chem. Soc., vol. 79, p. 1245. 



5 Silvestri, Pogg. Ann., vol. 157 (1876), pp. 165-172. 



6 Boussingault, Comptes Rendus, vol. 53 (1861), pp. 78-79. 



