THE CONSTITUENTS OF METEORITES 40 I 



the meteorites of Chateau Renard, Alfianello, Milena, Mocs, and 

 others. Its composition is about that of labradorite. Tschermak 

 regards the mineral as a fused feldspar, while Groth and Brezina 

 consider it a distinct species allied to leucite. Its straight, 

 sharply defined outlines, the existence of striae, and the absence 

 of any fused appearance make Tschermak's view difficult to 

 accept, though the mineral resembles the feldspars in so many 

 other respects. 



hicluded gases. — All meteorites which have so far been tested 

 give off on heating one or more of the following gases : Hydro- 

 gen, carbon monoxide, carbon dioxide, nitrogen, and marsh gas. 

 Comparing the iron meteorites with the stone meteorites in 

 regard to the kind of gases given off it is found that the former 

 are characterized by a high content of H and CO, the latter b}' 

 an excess of COg. The following table of analyses of gases 

 from eight iron and six stone meteorites, quoted from Cohen, 

 gives an idea of the relative quantity of each gas : 



H CO CO2 N CH4 



Iron meteorites 63.09 20.70 8.12 7,52 0.57 



Stone meteorites 17.55 4-15 71.66 2.20 4.17 



The volumes of the gases obtained vary from 0.97 of a volume 

 given off from the iron of Shingle Springs to 47.13 volumes col- 

 lected from the Magura iron. The average number of volumes 

 obtained from the meteorites quoted in the above table is 2.82. 

 The gases in meteorites appear therefore to be under a somewhat 

 greater pressure than that of the earth's atmosphere. It has often 

 been urged that the gases obtained from meteorites by the meth- 

 ods above mentioned may have been absorbed from our own atmos- 

 phere. It is known on the one hand that terrestrial rocks give off on 

 treatment gases very similar in kind and quantity to those obtained 

 from meteorites. Thus Wright obtained from one ordinary trap 

 rock ^ of a volume of gas, 13 per cent, of which was COg and 

 the remainder chiefly hydrogen, and from another, one volume 

 of gas containing 24 per cent. CO3 and the remainder chiefly 

 hydrogen. Tilden has also recently shown that "the crystalline 

 rocks of the surface of the earth contain very notable quantities 



