IN rilKMlSTBY. 



bininj: weight, 16 ; density, 8). Whon tho mud at the bottom of 

 stagnant pool* i* ntirreii, bulihli-s ut this gaa rue to the surface; 

 im.i \\ in'i. mi\i-il with the upontaneotwly inflammable gnu, phoft- 

 l-h. .r.-ttod hydrogen, the bubble* ignite, giving rue to the iynit 

 r the ' Will-o'-tho-Wisp." In collieries it exude* from 

 the coal-beds, and often in such quantities a* to come with a 

 hissing noise from tho seams, called by the minors " blowers." 

 Here, when mixed with a certain quantity of air, it becomes tho 

 dangerous "fire-damp." In many parts of the world it issues 

 from the ground, and is utilised by the inhabitants as a source 

 of light uii'i 



rat inn. Tho gas may bo artificially procured by heating, 

 in a flask of German glass, sodium acotato mixed with caustic 

 soda. Considerably under rod-heat tho gas comes off, and may 

 be secured in tho usual way. The reaction may be thus 

 expressed 



NaOC.H.O + HNaO = Na,CO, + CH 4 ; 

 tho product remaining in tho retort being sodium carbonate. 



The gas is without colour, taste, or smell ; it burns, in tho 

 proaenco of oxygen, with a bluish flamo, into carbonic acid and 

 water : 



CH 4 4- 4O = CO, + 2H,O. 

 2+4 = 2 + . 



On reference to the numerals, it will be seen that for the com- 

 plete combustion of marsh gas a double quantity of oxygen is 

 required, or ten volumes of air. It will also be noticed that 

 one-half the volume of oxygen makes the carbonic acid gas, 

 whilst the other half becomes water with the hydrogen. This 

 fact enables us to analyse marsh gas by means of the eudio- 

 meter. Seeing the explosion is very violent, it is better not to 

 use pure oxygen, but air, adding to the quantity of gas in tho 

 instrument at least ten times its volume of air. After the 

 spark has passed, the diminution will indicate tho quantity of 

 gas which has become water; and as this water possesses all 

 the hydrogen of the gas, its composition is discovered. 



Marsh gas may be decomposed by a series of electric sparks 

 being passed through it, or if the gas be sent through a tube 

 heated to whiteness. Tho carbon is deposited, and a volume 

 of hydrogen, double that of the gas, is received. This will be 

 indicated by the numerals 



CH, = C + 4H. 

 2 =+4. 



This gas is tho chief ingredient of " coal gas." 



Ethylene, Olefiant Gas, or Heavy Carburetted Hydrogen (symbol, 

 CjH 4 ; combining weight, 28; density, 14). It is one of the 

 minor constituents of coal gas. It may be obtained by heating 

 in a flask one measure of alcohol and two of sulphuric acid. 

 Alcohol may bo considered as composed of olefiant gas and 

 water. It is deprived of this hitter by tho sulphuric acid, 

 thus: 



Alcohol, C,H O = C a H 4 4- H,0. 



Tho gas, to purify it, should be passed through a tube packed 

 with pieces of pumice stone, soaked with sulphuric acid (this 

 retains any alcohol vapour and ether in tho gas), and then 

 through caustic potash, which deprives it of sulphurous acid, 

 and carbonic acid, if any bo present. Tho gas has no colour, 

 but a feeble ethereal odour. It can be liquefied under great 

 pressure. It burns in contact with tho air very brightly. 



C 3 H t + 6O = 20O, + 2H.O. 



2 +6=2 + . 



This equation shows that tho products are carbonic acid and 

 water, and tho numbers indicate that tho gas requires for its 

 combustion three times its volume of oxygen, or fifteen of air. 

 Its constitution may bo determined by the eudiometer. When 

 strongly heated, it deposits half its carbon, and becomes marsh 

 gas without change of volume. If the heat bo very intense, tho 

 whole of the carbon is separated, and twice the volume of 

 hydrogen remains. 



These processes are explained in the following equations : 

 C,H. = CH. -t- C 

 2 =2 + . 

 And 



C,H. = 2C + 4H 

 2 = - + 4. 



It takes its name, olefiant, from tho fact that it forms, with 

 shlorine, a heavy, oily liquid called Dutch liquid. 



Coal Gat. Cot! (M, no generally tued for illuminating pur- 

 pose*, in procured by the deetraetive distillation of coal, * prooM 

 which is effected by exposing the coal to a high heat in cart-iron 

 tubes called retort*. Coke remain* in the retort, and Tmriou 

 volatile product*, together with a mixture of aome dosen ffMe*. 

 pus into the condmuen and purifier*. Many of the** retort* 

 are heated in the same furnace, and a pipe from each dips into 

 the main, which U a tube of great diameter, haJf.fiU.Al with 

 water, beneath tne surface of which the pipe* from the retorts 

 dip. As the products of the distillation p*M through thu 

 water, tho tar, an ammoniacal liquid called yat liquor, *ad water, 

 , whilst tho gas bubbles through and U carried away 

 by the main to tho purifier*, and thence to tho gasometer. 



Tho tar has proved productive of many useful sal: 



H 



CH. 

 C,H 

 C.H. 



CO, 

 H.S 







cw, 



CS, 

 C.H.. 



such as the aniline colours, mauve, magenta, etc. From the 

 ammoniacal liquid wo derive our chief supply of ammonia. The 

 gas in tho main is a mixture of 



Hydrogen . 



Marsh gas . 



Olefiant go* 



Butyline (oil gas), traces 



Carbonic oxido . 



Carbonic acid 



Sulphide of hydrogen 



Nitrogen . 



Cyanogen, a trace 



Vapour of bisulphide of carbon 

 ,, benzole 



Of these the sulphide of hydrogen, the bisulphide of carbon, and 

 carbonic acid gas are not only useless, but injurious. 



To remove them thu gas is exposed to a surf ace of ilaked lime; 

 this retains tho sulphide of hydrogen and carbonic acid. The 

 bisulphide of carbon may be removed by pacing the gas through 

 a tube filled with slaked lime, maintained at a temperature of 

 250 Cent. Under these circumstances the bisulphide is de- 

 composed. The presence of this compound is so minute that 

 its separation is seldom attempted ; yet it is chiefly duo to it 

 that plants cannot live in rooms lit with gas. Purified gas, 

 therefore, consists of marsh gas, olefiaut gas, oil gas, and other 

 hydro-carbons ; carbonic oxide, hydrogen, and nitrogen. An 

 idea of tho relative quantities of these gases may be had from 

 an analysis, mado by Bunsen, of a Manchester gas : 



45-58 



Marsh gas 



Carbonic oxido 



Olefiant gas . 



Butyliue 



Sulphide of Hydrogen 



Nitrogen 



Carbonic acid 



34-90 

 6-6* 

 4-08 

 2-38 



246 

 367 



100-00 



What causes the luminosity of flame f The presence in the 

 flame of a solid. If sulphur be ignited, it burns with a blue 

 non-luminous flame ; because the product of the combustion U 

 not a solid, but a gas (SO.). Phosphorus, on the 

 other hand, has a luminous flame, because the result 

 of the action is a solid, phosphoric acid, the particle* 

 of which being heated in the chemical action, be- 

 come white hot, and emit light. 



A striking instance of this truth is offered in the 

 oxy-hydrogen light. The flame of the gas is scarcely 

 visible, but when it plays upon a piece of lime (a 

 solid), it raises it to a white heat, and a brilliant light m- 

 is the result. Therefore, those gaaes are tho illumi- 

 nators of "coal gas," which contains carbon, the only 

 solid in the list except the trace of sulphur. The gas 

 will not give light unless this carbon be in a frte 

 state, and while in this state heated to a white heat. 

 In considering the structure of flame, the conditions 

 which secure this result will become evident. 



Flame. The flame of a candle u supported by *"* ** 

 the decomposition of the tallow, etc., of which it is 

 composed, into the vapours of hydro-carbons. This decompo- 

 sition is furthered by tho melted fat being spread over the wick 

 by capillary action. In the non-luminous cone, m (Fig. 89), 

 the vapours are rising from the wick ; in the other .two cones, 

 i and e, these vapours mix with air, and chemical action 

 ensues. 



Only a certain limited quantity of air can mix with the 



