158 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



burnt to water, leaving a gaseous residue consisting of 

 hydrogen and carbonic oxide in equal proportions. 



The contrast between marsh gas and olefiant gas is shown 

 by the equations : 



marsh gas (sparked) > carbon + hydrogen 

 i vol. 2 vols. 



olefiant gas (sparked) ^ carbon + hydrogen 

 i vol. 2 vols. 



I marsh gas + oxygen > carbonic anhydride + water 

 i vol. 2 vols. i vol. 



olefiant gas + oxygen > carbonic anhydride + water 

 i vol. 3 vols. 2 vols. 



Goal gas. The inflammable COAL GAS obtained by distil- 

 ling coal consists largely of marsh gas. Dalton, in describing 

 the properties of marsh gas, writes : 



" This gas is obtained nearly pure also^by distilling pit-coal 

 with a moderate red heat. It is now largely used as a 

 substitute for lamps and candles, under the name of coal gas. 

 According to Dr. Henry's analysis, coal gas does not usually 

 contain more than 4 or 5 per cent, of carbonic acid, sulphur- 

 etted hydrogen, and olefiant gas. The rest is principally 

 carburetted hydrogen, but mixed with some atoms of 

 carbonic oxide and hydrogen. The last portion of gas 

 driven off from pit-coal, seems to be entirely carbonic oxide 

 and hydrogen. The distillation of wood and of moist char- 

 coal, and many other vegetable substances, produces 

 carburetted hydrogen, but highly charged with carbonic acid, 

 carbonic oxide and hydrogen ; the two last gases always 

 appear exclusively at the end of the process " (ibid. pp. 445- 



44 6). 



SUMMARY AND SUPPLEMENT. 

 A. CARBONIC OXIDE. 



Lassone, in 1776, prepared an inflammable oxide of carbon 

 by heating Prussian blue, and by heating zinc oxide with 

 charcoal, 



ZnO -I- C _*> Zn + CO. 



