GAS, COAL 545 



Light carburetted hydrogen when pure is colourless, tasteless, and inodorous ; it is 

 neutral to test papers, and nearly insoluble in water ; its specific gravity is '6594:, and 

 100 cubic inches, at 60 Fahr. and 30 inches barometric pressure, weigh 17*4166 

 grains. It does not support combustion or respiration, but is inflammable, burning 

 with a blue, or slightly yellow flame, yielding scarcely any light. Mixed with a duo 

 proportion of atmospheric air or oxygen, and ignited, it explodes with groat violence : 

 the products of its combustion are water and carbonic acid. 



When light carburetted hydrogen is exposed to a white heat, it is slowly decomposed, 

 depositing carbon, and yielding twice its volume of hydrogen. 



Carbonic Oxide. This gas consists of 6 parts by weight of carbon, and 8 parts 

 of oxygen. Ife is formed when carbon is consumed in a limited quantity of air or 

 oxygen, and is also generated, as stated above, when steam is passed over ignited coko 

 or charcoal, or when coal-tar and steam meet in a red -hot vessel. It is always a con- 

 stituent of coal-gas. 



Carbonic oxide is a colourless and inodorous gas, rather lighter than atmospheric 

 air, and having exactly the specific gravity of olefiant gas, "9727 ; it is very sparingly 

 soluble in water, but is very soluble in ammoniacal solution of chloride of copper. 

 Carbonic oxide is inflammable, burning with a beautiful blue flame almost devoid 

 of light ; the product of its combustion is carbonic acid. It is said to be very 

 poisonous. 



III. IMPUEITIES. 



Sulphuretted Hydrogen. This gas consists of sixteen parts of sulphur and one part 

 of hydrogen ; it may be produced by passing hydrogen along with the vapour of 

 sulphur through a red-hot tube, but it is best prepared pure by decomposing proto- 

 sulphuret of iron with dilute sulphuric acid, and collecting the evolved gas at the 

 pneumatic trough or over mercury. It is always an ingredient in crude coal-, peat-, or 

 wood-gas. 



Sulphuretted hydrogen is a colourless gas, of a very nauseous odour, resembling 

 that of putrid eggs : its specific gravity is 1 '174:7. It is highly inflammable, burning 

 with a blue flame, destitute of light, and generating a large amount of sulphurous acid ; 

 it is chiefly this latter circumstance which renders its presence in coal-gas objectionable. 

 It is readily absorbed by metallic solutions, by hydrated oxide of iron, and by lime both 

 in the wet and dry states, and is easily recognised in coal-gas by exposing a strip of 

 paper impregnated with acetate of lead to a stream of the gas ; if the paper becomes 

 discoloured, sulphuretted hydrogen is present. 



Hydrosulphate of sulphide of Ammonium. This compound is formed by the combina- 

 tion of equal volumes of ammonia and sulphuretted hydrogen. It consists of 14 parts by 

 weight of nitrogen, 15 of hydrogen, and 32 of sulphur. It is always largely produced in 

 the manufacture of coal-gas, but is almost completely condensed and retained in the 

 aqueous layer of liquid products, contributing principally to the unbearable odour of 

 gas liquor ; a mere trace of this body is therefore present in crude coal-gas. When 

 quite pure it is a colourless crystalline solid, very soluble in water, and volatile at 

 ordinary temperatures. Its vapour, when present in coal-gas, is absorbed and decom- 

 posed by hydrate of lime both in the wet and dry states, ammonia being liberated. It 

 is also decomposed by acids, but in this case the ammonia is retained by the acid, whilst 

 sulphuretted hydrogen is evolved. 



Carbonic Acid. This gas is met with in nature as a constituent of atmospheric air, 

 and is produced in large quantities during the earlier stages of the formation of coal 

 in the earth's strata. Thus, in the lignite districts of Germany, it is copiously evolved, 

 and meeting with water in its passage to the surface, it is absorbed, and forms those 

 sparkling mineral springs commonly known as seltzer-water. 



_ Carbonic acid is also formed during fermentation, by the combustion of carbon in 

 air, and in the decomposition of water by carbon at a red heat. 



At ordinary temperatures carbonic acid is a colourless and invisible gas, but it may 

 be liquefied by very intense cold or pressure. It consists of 6 parts, by weight of 

 carbon united with 16 parts of oxygen, and thus differs from carbonic oxide by con- 

 taining twice as much oxygen as the latter gas. By passing carbonic acid over 

 ignited coke, charcoal, or other carbonaceous matters, it takes up as much carbon as 

 it already contains, and becomes converted into carbonic oxide; but it is impossible 

 in this way to convert the whole of the carbonic acid into carbonic oxide unless the 

 process be very frequently repeated. Carbonic acid is pungent, acidulous, and soluble 

 in an equal bulk of water, to which it communicates that briskness which we so much 

 admire in soda-water; it is considerably heavier than atmospheric air, its specific 

 gravity being 1-524. This gas is uninflammable, and cannot support combustion or 

 animal life. Its acid properties are not strongly developed, but it unites readily with 

 alkaline bases, forming carbonates : it is upon this property that the femoral of car- 



VOL. II. N N 



