264 MB. JOHN LEIGH ON THE CHEMICAL CHANGES 



being then unlike, the results of the application of heat or 

 other agents must also be unlike, analogous but yet unlike. 

 Both give off gases, but those of ooal are richer in car- 

 bon ; both give off oils, but those of coal are richer in carbon. 

 Naphtha is the turpentine of coal. The products of coal are 

 alkaline ; those of wood, acid^ arising from the large relative 

 quantity of oxygen that the latter contains (C. 36, H. 22, 

 O. 22, being the composition of wood); C. 24, H. 13, O. 

 being that of coal. The oxygen in wood seizes the hydro- 

 gen, and diminishes the production of illuminating gases — 

 the gases found consisting of carbonic acid, light carburetted 

 hydrogen, and very little defiant gas ; the oxygen also 

 seizes on the combined hydrogen and carbon, forming acetic 

 acid, a compound of C. 4, H. 3, O. 3, pyroxilic spirit (wood 

 naphtha, wood spirit), a kind of alcohol containing (C. 2, 

 H.4, 0.2), xylite (C. 12, H. 12, 0. 5),another liquid (C. 21, 

 H. 23, O. 10); all compounds containing a large amount of 

 oxygen, and from which it will be seen how important a 

 part the large amount of this element contained in wood 

 plays in the products of its destruction, and modifies the 

 results of its distillation. The gases from wood and from 

 peat, as well as from brown coal (wood coal), possess a very 

 low illuminating power. Coal is a compound of carbon, 

 hydrogen, a little oxygen, very little nitrogen, earthy con- 

 stituents constituting its ashes, sulphur in the form of 

 sulphuret of iron (iron pyrites), and in cannel occasional 

 layers of sulphate and carbonate of lime. Its empirical 

 formula is C. 34, H. 13, O. When distilled at a high tem- 

 perature in close vessels, part of the hydrogen unites with 

 carbon, forming light carburetted hydrogen, defiant gas, 

 gaseous hydro-carbons, naphtha, and its associated oils. 

 Another part unites with oxygen, forming water ; another 

 with nitrogen, forming ammonia; a fourth with sulphur, 

 forming sulphuretted hydrogen ; and a fifth with cyanogen, 

 forming prussic acid. Of the carbon, part unites with hydro- 



