390 PRINCIPLES OF CHEMISTRY 



dominates, the volume of carbonic oxide being comparatively less, 

 whilst the amount of carbonic anhydride increases as the temperature 

 of the reaction decreases (generally it is more than 3 per cent.). 



Metals, like iron and zinc, which at a red heat are capable of 

 decomposing water with the formation of hydrogen, also decompose 

 carbonic anhydride with the formation of carbonic oxide ; so both 

 the ordinary products of complete combustion, water and carbonic 

 anhydride, are very similar in their reactions and hydrogen may 

 be compared with carbonic oxide. The metallic oxides of the above- 

 mentioned metals, when reduced by charcoal, also give carbonic oxide. 

 Priestley obtained it by heating charcoal with zinc oxide. It must be 

 held that here carbonic anhydride is first produced, but that, combining 

 with carbon, it forms carbonic oxide. As free carbonic anhydride may 

 be transformed into carbonic oxide, so, in the same way precisely, may 

 that carbonic acid which is in a state of combination ; therefore, if 

 magnesium or barium carbonates (MgCO 3 or BaCO 3 ) be heated to a 

 red heat with charcoal, orlron or zinc, carbonic oxide will be produced 

 for instance, it is obtained by heating an intimate mixture of 9 parts 

 of chalk and 1 part of charcoal in a clay retort. 



Many organic substances 27 on being heated, or under the action of 

 different agents, yield carbonic oxide ; amongst these are many organic 

 or carboxylic acids. The simplest are formic and oxalic acids. Formic 

 acid, CH 2 O 2 , on being heated to 200, easily decomposes into carbonic 

 oxide and water, CH 2 O 2 = CO + H 2 O. This reaction may be effected 



side of the question resolves itself into utilising all the heat given out by the charcoal, 

 and contained in the incandescent gas, for heating up the air, for the formation and super- 

 heating of the steam. 



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 (page 172) 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 

 carbu retted that is, mixed with the vapours of volatile hydrocarbons (generally benzene 

 or naphtha, naphthalene, or simply naphtha gas), which communicate to the pale flamo 

 of carbonic oxide and hydrogen a great brilliancy, owing to the high temperature ( 1 r \ ( 1 . ] > . < 1 

 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, may be pro- 

 duced from any kind of fuel, and ought to be much cheaper than ordinary gas, it may 

 actually be considered that in course of time (when practice will 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 air 

 inconvenient. At present its consumption spreads principally for lighting purposes, and 

 for use in gas-engines instead of ordinary illuminating gas. 



7 The so-called yellow prussiate, K 4 FeC 6 N 6 , on being heated with ten parts of strong 

 sulphuric acid forms a considerable quantity of very pure carbonic oxide completely free 

 from carbonic anhydride. 



