116 



UNDULATORY FORCES. LIG II T. 



[IMITKITIKX Or GAS. 



coal are annually ooninmed in England in the manufac- 

 ture of gas; and at each ton of coal, on the average, 

 product* about 10,000 cubic feet of gad, we hare the 

 almost incredible quantity of 60,000,000,000 cubic foet 

 of gas produeed~yarly. 



Action of lleat on Organic Matter. As a preliminary 

 to the study of gas-making, it is necessary that some- 

 thing should be known of the changes which occur li.-n 

 animal or vegetable matter is subjected to the action of 

 heat Chemists have shown that the effects vary with 

 the temperature. At first, when the heat is not con- 

 siderable, the matters evolved consist of aqueous vapour, 

 organic acids, ammonia, and various combustible fluids 

 h are soluble in water. In the second period, when 

 the heat is somewhat higher, the products are carbonic 

 acid, carbonic oxide, water, and a number of oleaginous 

 or empyreutnatic compounds, which are not soluble in 

 water ; and lastly, when the temperature is still higher, 

 the products of the decomposition are hydrogen, marsh 

 gas, and sundry hydro-carbons, which retain their gaseous 

 condition. In the case of non-nitrogenous bodies, as 

 wood, resin, fat, oil, <tc., the chief products of distilla- 

 tion are water, acetic acid, naphtha or wood-spirit, vola- 

 tile oil, tar, paraffine, creosote, carbonic acid, carbonic 

 oxide, olefiant gas, super-olefiaut gas, marsh gas, hydro- 

 gen, >tc. ; and when the substance contains nitrogen and 

 sulphur, as is the caso with coal, there are evolved am- 

 monia, aniline, leukol, picoline, lutidine, <fcc., together 

 with cyanogeu, sulpho-cyanogen, and most of the com- 

 pounds just named. In every case there remains in the 

 retort a quantity of carbonaceous matter, which goes by 

 the name of coke. 



Of the gases which are thus evolved, the most impor- 

 tant are hydrogen, carbonic oxide, marsh gas, olctiant gas, 

 and various hydro-carbons which give to gas its high 

 illuminating power: all the others are positively injuri- 

 ous, and ought, therefore, to be got rid of before the gas 

 is supplied to the public. An examination of the quality 

 of these gases will readily convince us that they may be 

 divided into three kinds namely, the light-giving gases, 

 the diluters, and the positive impurities. Of the light- 

 giving gates, the following are the most important : 



(a.) Olefiant g<u (C'H 1 ): a compound that was dis- 

 covered in the year 1795, by the associated Dutch che- 

 mists, and was so named from the property which it lias 

 of forming an oily-looking fluid when it combines with 

 chlorine. It is an odourless gas, and has a specific gra- 

 vity of 0-97. It burns with a bright yellow flame, and 

 consumes three times its bulk of oxygen, or nearly fifteen 

 times its bulk of atmospheric air, producing twice its 

 volume of carbonic acid. The gas is readily condensed 

 by chlorine, bromine, and anhydrous sulphuric acid ; it 

 is also absorbed to a slight extent by water. 



(h.) Other hydro-carbons, as Propylene (OH' 1 ), or the 

 super-oleuant gas of Dalton and Henry, Etherene (11 ,. 

 or the volatile gas of Faraday, and perhaps some others 

 of a like atomic composition, are met with in most of the 

 illuminating gases of commerce. These, like the last, 

 consist of equal proportions of carbon and hydrogen. 

 They are very condensible by chlorine, bromine, and 

 anhydrous sulphuric acid, and they burn with a very 

 bright sooty flame. 



The diluting gases are marsh gas, hydrogen, and car- 

 bonic oxide. These are important constituents of com- 

 mon gas, because they serve as the purveyors of the rich 

 illuminating hydro-carbons, which could not be burnt 

 alone. 



(a.) Marsh gas, or light carburetted hydrogen, is a com- 

 pound of one atom of carbon and two of hydrogen (CH 1 ). 

 It is about half as heavy as atmospheric air, and it hunts 

 with a bluish flame, tipped with yellow. It consumes 

 twice its bulk of oxygen, or nearly ten times its bulk of 

 air ; and it produces its own volume of carbonic acid. 



('.) Ifiiilnxjrn is the lightest of all known substances. 

 It weighs but a fifteenth of its bulk of atmospheric air. 

 It burns with a pale blue flame, and consumes only half 

 its bulk of oxygen, or two-and-a-half times its bulk of 

 air; the sole product of its combustion being aqueous 

 vapour. 



(c.) Carbonic oxide (CO) is a little lighter than atmo- 

 spheric air. It bums like the preceding, with a blue 

 flume, and consumes only half its volume of oxygen. 

 The product of its combustion is its own bulk of carbonic 

 acid. 



The imjtuntifs of gas are carbonic acid, ammonia, sul- 

 phuretted hydrogen, bisulphuret of carbon, tarry matter, 

 and various compounds of cyanogen and sulphur. 



(a.) Carbonic acid (CO 1 ) is a very heavy gas its den- 

 sity being about I '5. It is not only incomoustible, but 

 lias the power of checking the combustion of all infUm- 

 mable gases. It is freely absorbed by lime and alkalies. 

 Water takes up about its own bulk of the gas. 



(&.) Ammoniacal gas (NH 3 ) is about half as heavy as 

 atmospheric air. It is not combustible, unless it is de- 

 composed by the heat of some other burning body ; and 

 then the hydrogen of the gas burns in the usual manner. 

 Ammonia is readily absorbed by water, and by solutions 

 of acids and metallic salts. It is known by its communi- 

 cating a red colour to turmeric paper, and by fuming 

 with muriatic acid. 



(c.) Sulphuretted hydrogen (HS) is a most unpleasant- 

 smelling compound ; it is a little heavier than atmospheric 

 air, and burns with a pale-blue flame that evolves the 

 odour of a burning match. When plenty of atmospheric 

 air is present, the products of its combustion are water 

 and sulphurous acid ; but if the supply is limited, water 

 alone is formed, and the sulphur is precipitated. The 

 sulphurous acid, when produced, quickly absorbs more 

 oxygen, and becomes sulphuric acid a compound that 

 exerts a most destructive influence on every kind of tex- 

 tile fabric. When sulphuretted hydrogen escapes into 

 the air without burning, it discolours lead paint, and 

 tarnishes silver. On these accounts, sulphuretted hydro- 

 gen is regarded as one of the most injurious compounds 

 of ordinary gas. It is absorbed by lime, and by the salts 

 of iron, zinc, copper, and lead ; and the test for it is a 

 piece of white paper dipped in a solution of sugar of lead. 

 On exposing such paper, while damp, to the action of 

 the gas, the lead-salt is quickly discoloured ; and thus 

 the smallest trace of sulphuretted hydrogen may be easily 

 recognised. 



(d.) Bisulphuret of carbon (CS f ) is even a more serious 

 impurity than the last, for it not only produces the same 

 acid compound by its combustion, but is also more diffi- 

 cult of detection ; and then, again, chemists are not yet 

 acquainted with any process for the removal of this 

 noxious' body from the gas of commerce. All tin ' 

 circumstances give it an importance that it would not 

 otherwise possess. Bisulphuret of carbon, when pure, 

 is an oily-looking liquid, that sinks in water. It evolves 

 the unpleasant odour of putrid cabbage, and boils at a 

 temperature of 100 Fall. ; it burns with a blue flame, 

 and its vapour consumes twice-and-a-half its bulk of 

 oxygen, or nearly twelve-and-.vhalf times its bulk of 

 atmospheric air, producing twice its volume of sulphurous 

 acid, and half its volume of carbonic acid. This com- 

 pound is best recognised by burning the gas, and col- 

 lecting the products, in which sulphurous or sulphuric 

 acid will be discovered. 



(f. ) The tarry matters of inflammable gas are of a very 

 complex nature ; they appear to be held in solution by 

 ammonia, and to be precipitated in the form of dark 

 flakes, when the gas is made to pass through a vessel 

 containing flints moistened with acid. It is very pro- 

 bable thit tl'eso tarry matters are of an acid nature, 

 and that, in their union with ammonia, they produce 

 compounds that are sufficiently volatile to be suspend I 

 in the gas. 



(/.) The cyanogen compounds are not likely to be 

 found in the gas of commerce, for they are readily 

 absorbed by the lime made use of in its purification. ( )f 

 these, cyanogen, hydrocyanic acid, and sulpho-cyanogen 

 are the most important. 



The Manufacture of Gas. In all cases, the destructive 

 distillation of the organic substan'* which yields the gas 

 is effected in a vessel called a retort, which is set in 

 a furnace ; and the gaseous products are purified by 

 transmitting them through a series of vessels named 



