74 



THAT S IT : 



igniting, joined to them burners 

 g of clay, 10. In the 

 coal districts of Great 

 Britain, frequent ex- 

 plosions in coal-mines 

 arise from escapes of gas. 

 Another description of 

 gas rises over marshes, 

 where, spontaneously 

 igniting, it causes Will- 

 ow -the- Wisps, 11. 



Eor a hundred years 

 after it was known that 

 gas might be distilled 

 from coal, it was used 

 only to produce an interesting 



317. 



318. 



experiment, being burnt from 

 bladders, and 

 vaguely de- 

 scribed as a 

 sort of inflam- 

 mable air or 

 spirit. About 

 1790, a Mr. 

 Murdock, of 

 Cornwall, em- 

 ployed gas to 

 light him in 

 nightly walks, 

 by burning it 

 from bladders. 12. 



319. 



For this he was regarded as a 

 wizard. He conceived the idea 

 that gas might be conveyed 

 through pipes, and used to light 

 the houses and streets ; he soon 

 demonstrated the truth of his 

 opinions by lighting up his own 

 house and offices at Redruth, and 

 afterwards several large factories- 

 In 1813, the manufacture of gas 

 extended to London; and, in 

 1814, Westminster was partially 

 lit with it. 



Observing burning coal, 13, we 

 find the non-heated portions 



320. 



black, the heated pieces emitting 

 flame and smoke, 14, while that 

 which has arrived at a red-heat, 

 glows with fire, but gives off 

 neither smoke nor flame. Coal is 

 chiefly a compound of two sub- 

 stances, carbon and hydrogen. 

 Carbon burns without flame; but 

 hydrogen produces flames abun- 

 dantly. The red-fire is caused by 

 the burning of carbon; the flames 

 by the burning of hydrogen. The 

 flames of pure hydrogen produce 

 a very feeble light ; but when 

 hydrogen is driven from coals, it 



