are nearly equal.
[26] Water gas, obtained from steam and charcoal at a white heat, contains about 50 p.c. of hydrogen, 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 anhydride could be as readily obtained in as pure a state as water, then CO might be prepared directly from CO2 + C, and in that case the utilisation of the heat of the carbon would be the same as in water gas, because CO evolves as much heat as H2, and even more if the temperature of the smoke be over 100°, and the water remains in the form of vapour (Note [25]). But producer gas contains a large proportion of nitrogen, so that its effective temperature is below that given by water gas; 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 where the gas can be easily distributed through pipes, water gas is at present held in high estimation, 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.
There are numerous systems for making water gas, but the American patent of T. Lowe is generally used. The gas is prepared in a cylindrical generator, into which hot air is introduced, in order to raise the coke in it to a white heat. The products of combustion containing carbonic oxide are utilised 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.
Water gas is sometimes called ‘the fuel of the future,’ because it is applicable to all purposes, develops a high temperature, and is therefore available, not only for domestic and industrial uses, but also for gas-motors and for lighting. For the latter purpose platinum, lime, magnesia, zirconia, and similar substances (as in the Drummond light, Chapter [III].), are rendered incandescent in the flame, or else the gas is carburetted—that is, mixed with the vapours of volatile hydrocarbons (generally benzene or naphtha, naphthalene, or simply naphtha gas), which communicate to the pale flame of carbonic oxide and hydrogen a great brilliancy, owing to the high temperature developed by the combustion of the non-luminous gases. As water gas, possessing these properties, may be prepared at central works and conveyed in pipes to the consumers, and as it may be produced from any kind of fuel, and ought to be much cheaper than ordinary gas, it may as a matter of fact be expected that in course of time (when experience shall have determined the cheapest and best way to prepare it) it will not only supplant ordinary gas, but will with advantage everywhere replace the ordinary forms of fuel, which in many respects are inconvenient. At present its consumption spreads principally for lighting purposes, and for use in gas-engines instead of ordinary illuminating gas. In some cases Dowson gas is prepared in producers. This is a mixture of water and producer gases obtained by passing steam into an ordinary producer (Note [19]), when the temperature of the carbon has become sufficiently high for the reaction C + H2O = CO + H2.
[27] The so-called yellow prussiate, K4FeC6N6, on being heated with ten parts of strong sulphuric acid forms a considerable quantity of very pure carbonic oxide quite free from carbonic anhydride.
[27 bis] To perform this reaction, the formic acid is mixed with glycerine, because when heated alone it volatilises much below its temperature of decomposition. When heated with sulphuric acid the salts of formic acid yield carbonic oxide.
[28] The decomposition of formic and oxalic acids, with the formation of carbonic oxide, considering these acids as carboxyl derivatives, may be explained as follows:—The first is H(COOH) and the second (COOH)2, or H2 in which one or both halves of the hydrogen are exchanged for carboxyl; therefore they are equal to H2 + CO2 and H2 + 2CO2; but H2 reacts with CO2, as has been stated above, forming CO and H2O. From this it is also evident that oxalic acid on losing CO2 forms formic acid, and also that the latter may proceed from CO + H2O, as we shall see further on.
[28 bis] Greshoff (1888) showed that with a solution of nitrate of silver, iodoform, CHI3, forms CO according to the equation CHI3 + 3AgNO3 + H2O = 3AgI + 3HNO3 + CO. The reaction is immediate and is complete.
[29] It is remarkable that, according to the investigations of Dixon, perfectly dry carbonic oxide does not explode with oxygen when a spark of low intensity is used, but an explosion takes place if there is the slightest admixture of moisture. L. Meyer, however, showed that sparks of an electric discharge of considerable intensity produce an explosion. N. N. Beketoff demonstrated that combustion proceeds and spreads slowly unless there be perfect dryness. I think that this may he explained by the fact that water with carbonic oxide gives carbonic anhydride and hydrogen, but hydrogen with oxygen gives hydrogen peroxide (Chapter [VII].), which with carbonic oxide forms carbonic anhydride and water. The water, therefore, is renewed, and again serves the same purpose. But it may be that here it is necessary to acknowledge a simple contact influence. After Dixon had shown the influence of traces of moisture upon the reaction CO + O, many researches were made of a similar nature. The fullest investigation into the influence of moisture upon the course of many chemical reactions was made by Baker in 1894. He showed that with perfect dryness, many chemical transformations (for example, the formation of ozone from oxygen, the decomposition of AgO, KClO3 under the action of heat, &c.) proceeds in exactly the same manner as in the presence of moisture; but that in many cases traces of moisture have an evident influence. We may mention the following instances: (1) Dry SO3 does not act upon dry CaO or CuO; (2) perfectly dry sal-ammoniac does not give NH3 with dry CaO, but simply volatilises; (3) dry NO and O do not react; (4) perfectly dry NH3 and HCl do not combine; (5) perfectly dry sal-ammoniac does not dissociate at 350° (Chapter VII., Note [15 bis]); and (6) perfectly dry chlorine does not act upon metals, &c.
[30] Carbonic oxide is very rapid in its action, because it is absorbed by the blood in the same way as oxygen. In addition to this, the absorption spectrum of the blood changes so that by the help of blood it is easy to detect the slightest traces of carbonic oxide in the air. M. A. Kapoustin found that linseed oil and therefore oil paints, are capable of giving off carbonic oxide while drying (absorbing oxygen).