572 GAS, COAL 



for re-raeasuroraent, taking care to shut I before the caustic-potash solution roaches F, 

 the observed diminution in volume gives the amount of carbonic acid present. 



The amount of oxygon is determined in like manner by passing up into i a few 

 drops of a saturated solution of pyrogallic acid, which forms with the potash already 

 present pyrogallate of potash. The gas being then brought back into i, oxygon, if 

 present, will be absorbed in a few minutes. Its amount is of course ascertained by 

 re-measuring the gas in F. 



The next step in the operation consists in estimating the amount of olofiant gas and 

 illuminating hydrocarbons. For this purpose, whilst the gas, thus deprived of oxygen 

 and carbonic acid, is contained in F, the tube i must be removed, thoroughly cleansed 

 and dried, and being filled with mercury, must be again attached to I. The gas must 

 now be transferred from F to i, and a coke bullet, prepared as above described, being 

 passed up into i, must be allowed to remain in the gas for one hour. After its 

 removal, a few drops of a strong solution of bichromate of potash must bo admitted 

 into i in order to absorb the sulphurous acid and vapours of anhydrous sulphuric 

 acid resulting from the previous operation. The gas is now ready for measurement ; 

 it is therefore passed into F, and its volume determined ; the diminution which has 

 occurred since the last reading represents the volume of oleh'ant gas and illuminating 

 hydrocarbons that were present in the gas. 



It now only remains to determine the respective amounts of light carburetted hy- 

 drogen, carbonic oxide, hydrogen, and nitrogen present in the residual gas. This is 

 effected as follows: As much of the residual gas as will occupy about l inch of 

 its length at atmospheric pressure is retained in F, and its volume accurately deter- 

 mined ; the remainder is passed into j, and the latter tube removed, cleansed, filled 

 with mercury, and re-attached. A quantity of oxygen equal to about throe and a half 

 times that of the combustible gas is now added to the latter, and the volume again 

 determined ; then the mixture having been expanded to about the sixth division, an 

 electric spark is passed through it by means of the wires at m. The contraction 

 resulting from the explosion having been noted, two or three drops of caustic-potash 

 solution are passed into J, and the gas is then transferred into the same tube. In 

 two minutes the carbonic acid generated by the explosion is perfectly absorbed, and 

 its volume is determined by a fresh measurement of the residual gas. The latter 

 must now be exploded with three times its volume of hydrogen, and the contraction 

 on explosion noted. These operations furnish all the data necessary for ascertaining 

 the relative amounts of light carburettod hydrogen, carbonic oxide, hydrogen, and 

 nitrogen, according to the mode of calculation given here. 



Finally, the value of the luminiferous constituents is obtained as before, by 

 exploding about a cubic inch of the original specimen of gas with from four to five 

 times its volume of oxygen, and noting the amount of carbonic acid produced. 



ON THE MANUFACTURE OF COAL-G-AS. 



Coal-gas, as usually manufactured, is produced by exposing coal to a bright red 

 heat in retorts. The gas as it issues from the retort cannot be directly employed 

 for illumination, for it contains vapours of tar and naphtha, as also steam impregnated 

 with carbonate of ammonia and hydrosulphate of sulphide of ammonium. These 

 vapours would easily condense in the pipes through which the gas must be distributed, 

 and would produce obstructions ; they must therefore bo so far removed by previous 

 cooling, as to be liable to occasion no troublesome condensation at ordinary tem- 

 peratures. The crude coal-gas contains moreover sulphuretted hydrogen, whose 

 combustion would exhale an offensive sulphureous odour, that ought to be avoided 

 as much as possible. Carbonic acid enfeebles the illuminating power of the gas, 

 and should be removed. The disengagement of gas in the retorts is never uniform, 

 but varies at the different stages of the process ; for which reason the gas must be 

 received in a gas-holder, where it may experience uniform pressure, and bo discharged 

 uniformly into the pipes of distribution, in order to ensure a steady discharge of gas, 

 and uniform intensity of light in burners. A coal-gas apparatus ought therefore to bo 

 so constructed as not only to generate the gas itself, but to fulfil the above conditions. 



In Jig. 1026 such an apparatus is represented, whore the various parts are shown 

 connected with each other in section. 



A is the furnace, with its set of cylindrical or elliptical retorts, five in number. From 

 each of these retorts, a tube b proceeds perpendicularly upwards, and then by a curve 

 or saddle-tube, it turns downwards, where it enters a long horizontal cylinder under 

 B, shut at each end with a screw cap, and descends to beneath its middle, so as to dip 

 about an inch into the water contained in it. From one end of this cylindor, the 

 tube d passes downwards, to connect itself with a horizontal tube which enters into 

 ihQtarpitot cistern c, by means of tho vertical branch/. This branch reaches to 



