COMPOUNDS OF CARBON WITH OXYGEN AND NITROGEN 399 



glass- working, steel -melting, &c.), but great advantage also 23 is gained 

 as regards the quantity of fuel, because the transmission of heat to the 

 object to be heated, other conditions being equal, is determined by the 

 difference of temperatures. 



The transformation of carbonic anhydride, by means of charcoal, 

 into carbonic oxide (C + CO 2 = CO + CO) is considered a reversible 

 reaction, because at a high temperature the carbonic oxide splits up 

 into carbon and carbonic anhydride, as Sainte-Claire Deville showed by 

 using the method of the * cold and hot tube.' Inside a tube heated in 

 a furnace another thin metallic (silvered copper) tube is fitted, through 

 which a constant stream of cold water flows. The carbonic oxide 

 coming into contact with the heated walls of the exterior tube forms 

 charcoal, and its minute particles settle in the form of lampblack on 

 the lower side of the cold tube, and, since they are cooled, do not 

 act further on the oxygen or carbonic anhydride formed. 24 A series 



combinations do not ensue, possible temperatures being limited by reverse reactions. 

 Here, as in a number of other cases, the further investigation of the matter must prove 

 of direct value from a practical point of view 



25 At first sight it appears absurd, useless, and paradoxical to lose nearly one-third of the 

 heat which fuel can develop, by turning it into gas. Actually the advantage is enormous, 

 especially for - producing high temperatures, as is already seen from the fact that fuels rich 

 in oxygen (for instance, wood) when damp are unable, with any kind of hearth whatever, to 

 give the temperature required for glass-melting or steel-casting, whilst in the gas-producer 

 they furnish exactly the same gas as the driest and most carbonaceous f ue-1. In order to 

 understand the principle which is here involved, it is sufficient to remember that a large 

 amount of heat, but having a low temperature, is in many cases of no use whatever. We 

 are unable here to enter into all the details of the complicated matter of the application 

 of fuel, and further particulars must be sought for in special technical treatises. The 

 following footnotes, however, contain certain fundamental figures for calculations con- 

 cerning combustion. 



24 The first product of combustion of charcoal is always carbonic anhydride, and not 

 carbonic oxide. This is seen from the fact that with a shallow layer of charcoal (less 

 than a decimetre if the charcoal be closely packed) carbonic oxide is not formed at all. 

 It is not even produced with a deep layer of charcoal if the temperature is not above 500, 

 and the current of air or oxygen is very slow. With a rapid current of air the charcoal 

 becomes red-hot, and the temperature rises, and then carbonic oxide appears (Lang 1888). 

 Ernst (1891) found that below 995 carbonic oxide is always accompanied by CO 2 , and 

 that the formation of COo begins about 400. Naumann and Pistor determined that the 

 reaction of carbonic anhydride with carbon commences at about 550, and that between 

 water and carbon at about 500. At the latter temperature carbonic anhydride is formed, 

 and only with a rise of temperature is carbonic oxide formed (Lang) from the action of 

 the carbonic anhydride on the carbon, and from the reaction CO.> + H 2 = CO + H 2 O. 

 Bathke (1881) showed that at no temperature whatever is the reaction as expressed by the 

 equation C0 2 + C = 2CO 2 , complete; a part of the carbonic anhydride remains, and Lang 

 determined that at about 1,000 not less than 8 p.c. of the carbonic anhydride remains 

 untransformed into carbonic oxide, even after the action has been continued for several 

 hours. The endothermal reactions, C -t- 2H 2 = CO 2 + 2H 2 , and CO + H 2 O = CO 2 + H 2 ,. 

 are just as incomplete. This is made clear if we note that on the one hand the 

 above-mentioned reactions are all reversible, and therefore bounded by a limit ; and, on 

 the other hand, that at about 500 oxygen begins to combine with hydrogen and carbon, 



