

GAS, COAL 54,7 



that bisulphide of carbon is present. As a decisive test, 60 or 60 drops of the con- 

 densed fluid should be collected in a small test-tube, and a few drops of pure nitric 

 acid added : on heating this mixture to boiling-point over a spirit lamp, and then 

 adding a drop or two of a solution of chloride of barium, the liquid will become more 

 or less milky if bisulphide of carbon has been present in the gas. It is necessary 

 here to remark, that the absence of sulphuretted hydrogen must be first ascertained 

 by the non-colouration of paper imbued with acetate of lead, and held for some minutes 

 in a stream of the gas. . 



Nitrogen. This gas is the chief constituent of atmospheric air, 100 cubic feet of 

 air containing rather more than 79 cubic feet of this gas. It also enters into the 

 composition of a large number of animal and vegetable substances. All descriptions 

 of coal contain small quantities of this element. When nitrogen is eliminated from 

 combination in contact with oxygen, it usually takes the form of nitrous or nitric 

 acid ; whilst in contact with an excess of hydrogen it generates ammonia. It is in 

 this latter form that it is eliminated from coal in the process of gas-generation. 



Nitrogen is a colourless, inodorous, and tasteless gas, of specific gravity 0*976. It 

 is incombustible under ordinary circumstances, and instantaneously extinguishes 

 burning bodies. Under certain conditions, however, nitrogen does undergo combus- 

 tion, as when it is exposed to a very intense heat in the presence of oxygen. This 

 occurs, for instance, when a small quantity of nitrogen is added to a mixture of 

 hydrogen, with a somewhat larger proportion of oxygen than is requisite to form 

 water, and the mixture then ignited : a loud explosion takes place, and a considerable 

 quantity of nitric acid is formed, owing to combustion of the nitrogen, or in other 

 words, its union with oxygen gas. This formation of nitric acid possibly occurs also 

 to a limited extent during the burning of coal-gas ; and as the temperature required to 

 form nitric acid is very high, the greater the volume of gas consumed from one burner 

 in a given time, the greater will be the relative quantity of nitric acid produced. The 

 formation of such a corrosive material as nitric acid under these circumstances shows 

 the importance of preventing the admixture of the products of the combustion of coal- 

 gas with the atmosphere of the apartments in which it is consumed. The nitrogen 

 contained in coal-gas is due entirely to the admission of atmospheric air, and not to 

 the elimination of the nitrogen contained in the coal ; for this latter nitrogen appears 

 to be evolved only in combination with hydrogen as ammonia. As nitrogen is incom- 

 bustible, it is not only a useless ingredient in coal-gas, but, owing to its abstracting 

 heat from the flame of such gas, it causes a diminution of light, and is thus decidedly 

 injurious. The admixture of this element ought therefore to be avoided as much as 

 possible. 



Oxygen. This element is always present in coal-gas, although in very small quan- 

 tity if the manufacture be properly conducted. It is never evolved from the coal 

 itself, but it makes its way into the gas through leaky joints, and also to a certain 

 extent through the water in which the holders are immersed. Its presence is highly 

 injurious to the illuminating power of the gas ; and since, when once introduced, it 

 cannot be abstracted by any practicable means, its admixture ought to be carefully 

 guarded against. 



Oxygen is a colourless, invisible, and inodorous gas, very sparingly soluble in water, 

 and which has hitherto resisted all attempts to liquefy it by cold or pressure. It is 

 evolved from the leaves of plants under the influence of light, and constitutes about 

 one fifth of the bulk of our atmosphere. By far the largest amount of oxygen, how- 

 ever, exists in combination with other elements ; thus eight out of every nine tons of 

 water are pure oxygen, and it forms at least one third of the total weight of the 

 mineral crust of our globe. It is therefore the most abundant of all elements. 

 Oxygen gas is heavier than atmospheric air ; 100 cubic inches, at 63 Fahr. and 30 

 inches barometric pressure, weighing 34-193 grains, whilst 100 cubic inches of the 

 latter weigh only 31-0117 grains. The specific gravity of oxygen is 1*1026. It 

 eminently supports combustion, all combustible bodies when introduced into it 

 burning much more vividly than in common air ; indeed it is owing to the presence 

 of this gas in our atmosphere, that common air possesses the property of supporting 

 combustion. 



Aqueous Vapour. Water is volatile at all natural temperatures, and therefore its 

 vapour always exists to a greater or less extent diffused in coal-gas, even as delivered 

 to the consumer. The percentage amount of aqueous vapour thus present in coal- 

 gas is always small, even when the gas is saturated; nevertheless the presence of even 

 this small proportion of aqueous vapour diminishes to a certain extent the light pro- 

 duced by the combustion of gas. This effect is no doubt owing to the action of 

 aqueous vapour upon carbon at a high temperature, by which action hydrogen, 

 carbonic oxfde, and carbonic acid gases are produced. The presence of aqueous 

 vapour therefore tends to reduce the number of particles of carbon floating in the gas 



NK 2 



