D. CHEMISTRY AND METALLURGY. 209 



one per cent., and of great strength barely two per cent., of 

 the dry soluble matter. The evaporation residue consists of 

 a deep brown, shining, varnish-like mass, feeling quite dry 

 to the touch after two days. If the ordinary substitutes 

 are present, however, this residue becomes sticky after one 

 or two hours' standing, and quite damp in twenty -four 

 hours. 



ON THE GASES INCLOSED IN COAL. 



An examination of the gaseous substances contained in 

 coal, and also of the gases which are evolved from fissures in 

 coal-mines, has been made by Thomas. The coals which he 

 examined were of three sorts: the bituminous or house coals, 

 the semi-bituminous or steam coals, and the anthracite coals. 

 The samples examined all came from the South Wales coal- 

 basin. In obtaining the gas from the coal, slices were first 

 sawn from the middle of large cubical blocks, and a strip cut 

 from the centre of each of these six or eight inches long, and 

 five eighths of an inch square. This was then placed in a 

 hard glass tube, connected with a mercury pump, and ex- 

 hausted. Very little gas, however, was obtained in this way 

 only two or three cubic centimeters in 100 grammes of coal. 

 On placing the tube in boiling water, the exhaustion being 

 continued, gas was freely evolved. When it ceased, the tem- 

 perature was raised to 200 and even 300 Centigrade, where- 

 by additional quantities of gas were obtained. On analyzing 

 the gas, it was found to be composed of marsh gas, carbon 

 dioxide, nitrogen, and oxygen. The bituminous coals give 

 the minimum amount of gas, but the quantity of carbon diox- 

 ide contained in it is large. Steam coals come next, as much 

 as eighty-seven per cent, of the gas obtained from them being 

 methyl hydride, or marsh gas. Anthracite coals give more 

 gas than the others, one specimen giving 600 cubic centime- 

 ters of gas from 100 grammes of coal when heated to 100. 

 But at 200, 1000 c. c. were given off, and at 300, 1875 c. c. 

 In composition, the gas from anthracite closely resembles that 

 from steam coal. The examination of the eras collected from 

 fissures in the mine, as well as that obtained by boring the 

 blocks of coal, was almost pure marsh gas, the amount pres- 

 ent rising sometimes even to 97.65 per cent. 21 A, II., xiii., 

 September, 1875. 



