ro.MIMH'Nns OF CARBON WITH OXYGEN' AND NITROGEN 389 



4 volumes of a gas consisting of hydrogen and carbonic oxide (H 2 + CO) 

 is formed. This mixture of combustible gases is called water gas.^ 

 But aqueous vapour (and only when strongly superheated, otherwise 

 it cools the charcoal) only acts on charcoal to form a large amount of 

 carbonic oxide at a very high temperature (when carbonic anhydride 

 dissociates) ; it begins to react at about 500, forming carbonic 

 anhydride, according to the equation C + 2H 2 O = CO 2 -f2H 2 . Besides 

 this, carbonic oxide on splitting up forms carbonic anhydride, and 

 therefore water gas always contains a mixture 2G in which hydrogen pre- 



-"' A molecular weight of this gas, or 2 volumes CO (28 grams), on combustion 

 (forming CO 2 ) gives out 68,000 heat units (Thomsen 67960 calories). A molecular weight 

 of hydrogen, H 2 (or 2 volumes), develops on burning into liquid water 69000 heat units 

 (according to Thomsen 68300), but if it forms aqueous vapour 58000 heat units. Char- 

 coal, resolving itself by combustion into the molecular quantity of CO 2 (2 volumes), 

 develops 97000 heat units. From the data furnished by these exothermal reactions it 

 follows : (1) that the oxidation of solid charcoal into carbonic oxide develops 29000 heat 

 units ; (2) that the reaction C + CO 2 = 2CO absorbs 39000 heat units ; (8) C + H 2 O = H 2 + CO 

 absorbs (if the water be in a state of vapour) 29000 calories, but if the water be liquid 

 40000 calories (almost as much as C + CO 2 ); (4) C + H 2 O = CO 2 + 2H 2 absorbs (if the 

 water be in a state of vapour) 19000 heat units ; (5) the reaction CO + H 2 O = CO 2 + H 2 

 develops 10000 heat units if the water be in the state of vapour. 



Therefore it follows that 2 volumes of CO or H 2 burning into CO 2 or H 2 O develop 

 almost the same amount of heat, just as also the heat effects corresponding with the 

 equations 



are nearly equal. 



26 Water gas, obtained from steam at a white heat, contains about 50 p.c. of hydro- 

 gen, about 40 p.c. of carbonic oxide, about 5 p.c. of carbonic anhydride, the remainder 

 being nitrogen from the charcoal and air. Compared with producer gas, which contains 

 much nitrogen, this is a gas much richer in combustible matter, and therefore capable of 

 giving high temperatures, and is for this reason of the greatest utility. If carbonic anhy- 

 dride could be as readily obtained in as pure a state as water, there would be no differ- 

 ence in the heating powers of producer gas and water gas. As regards the utilisation of 

 the heat of the charcoal there is no difference, because on burning carbonic oxide gives 

 out almost as much heat as hydrogen even more if the smoke has a temperature above 

 100, and the water remains as vapour (Note 25). But water gas stands higher than 

 producer gas as regards the concentration of the fuel in its transformation into gas, and 

 therefore in places where a particularly high temperature is required (for instance, for 

 lighting by means of incandescent lime or magnesia, or for steel melting, &c.), and for 

 distributing through pipes at great distances, water gas is at present held in high esti- 

 mation, but when (in ordinary furnaces, re-heating, glass-melting, and other furnaces) a 

 very high temperature is not required, and there is no need to convey the gas in pipes, 

 producer gas is generally preferred on account of the simplicity of its preparation, 

 especially as for water gas such a high temperature is required that the plant soon 

 becomes damaged. 



Water gas is prepared (there are very many systems, but the American patent of T. 

 Lowe, of Norristown, Pennsylvania, is much used) in a cylindrical generator, into which 

 heated air is introduced, in order, by partial combustion of the coke, to heat the remainder, 

 &c., to a white heat. The products of combustion containing carbonic oxide are utilised 

 in a contrivance for superheating steam, which is then passed over the white hot coke. 

 Water gas, or a mixture of hydrogen and carbonic oxide, is thus obtained. The practical 



