Page:The American Cyclopædia (1879) Volume VII.djvu/649

GAS 637 pass in a series of n -shaped pipes, surrounded with water which is supplied from a cistern, entering at the bottom of the condenser and passing out at the top. This arrangement is not represented in the diagram, which also only shows a small portion of one condenser, of which there are usually three, through which the gas passes successively, being reduced in temperature in each. At the base of each con- denser are chambers into which the legs of the n-shaped pipes pass, the descending one, or that which carries the gas downward, extend- ing to near the bottom, beneath the surface of the tar and ammoniacal liquor, which then col- lects and passes off by suitably arranged pipes into the tar well. These tarry matters, to- gether with those collected in the hydraulic main, are the materials from which the beauti- ful aniline colors used in dyeing are made. (See ALIZARINE, ANILINE, ANTHEACENE, and COAL PRODUCTS.) From the condensers the gas is conducted into another apparatus for further separation of impurities. This is sometimes made of a box containing lumps of coke or fire brick moistened with water, and is then called a scrubber. At the Manhattan gas works, New York, a box, partially shown at &, called a washer, is used ; it consists of several separate vertical chambers, through which the gas is made to pass, under one partition and over the next, and during its passage subjected to the ac- tion of jets of water thrown into spray. In this way nearly all condensible and soluble impuri- ties are abstracted; but there remain several deleterious gases, the principal of which are sul- phuretted hydrogen and carbonic acid, which must be removed before the gas is fit to be delivered for consumption. Several methods have been devised for this purpose, such as passing the gas through milk of lime, which is called the wet-lime process, or through layers of moistened slaked lime, and also through layers of mixed protochloride of iron and 'quicklime, or sulphate of iron and slaked lime, the ferruginous salts being very effectual in removing all traces of sulphuretted hydro- gen. These slaked-lime purifiers are placed in large rooms, and require great care in man- agement, as well for safety as for effectiveness, the gas being liable to escape into the room and form an explosive mixture with the air ; and serious accidents have resulted from this cause. A single purifier is represented at & in the diagram. It consists of a tight double-sided tank from 4 to 6 ft. high and about 20 ft. long by 12 wide. A deep gutter runs around the upper edge, which is nearly filled with water for re- eeiving the edges of the lid, Z, by which means the apparatus is effectually sealed. It is usual to conduct the gas successively through three of these purifiers. In small works, especially those connected with the larger ones for ex- periment, the gas is forced from the retorts, by the pressure there created, through all the different pieces of apparatus; and formerly this was the only means of urging the gas on- ward in all of them. The pressure thus crea- ted in large works would so retard the flow of the gas from the retorts that it would suffer much decomposition with production of graph- ite carbon; and if clay retorts were used, much would escape through their walls. The difficulty is avoided by using what are called exhausters to take the gas from the washers and deliver it to the lime purifiers. These ma- chines may be in the form of a rotary fan blower, or of a cylinder and piston blowing machine. The lime purifiers have several lat- tice-work shelves, placed one above anoth- er and covered two or three inches in depth with freshly slaked lime. The gas entering at the bottom ascends through these layers of lime, which absorb the carbonic acid and sul- phuretted hydrogen and other impurities by the time it reaches the chamber beneath the lid. In the figure a pipe is seen passing from the bottom of the washer directly to the lime purifier. It has, however, been explained that the exhauster is placed between these two pieces of apparatus. A drawing of the ma- chine has been omitted in the cut from want of room, but the reader can supply the omis- sion. In the latter there is an orifice from which a pipe conducts the gas to the meter, from which it passes through the pipe o to the large reservoir, a small part of which is shown in the figure. In the following table of the constituents of purified coal gas, that in the first two columns is ordinary coal gas from Chemnitz, Saxony; in the third column, or- dinary London coal gas; and in the fourth, London cannel coal gas : CONSTITUENTS. 1. 2. 3. 4. Hydrogen 51-29 50-08 46*0 27-7 Marsh gas 8(5-45 85*92 89 -5 50'0 Carbonic oxide 4-45 5-02 7'5 6'8 Olefiant gas (elayl) Nitrogen 4-91 1'41 5-33 1'89 3-8 0'5 13-0 0'4 Oxygen 0'41 0-54 Carbonic acid Aqueous vapor 1-08 1-22 0-7 2-0 o-i 2'0 There are other heavy hydrocarbon gases be- sides elayl, or olefiant gas, as acetylene, trityl, and ditetryl, and also a small quantity of hy- drocarbon vapors, which yield light; but the illuminating power of the gas may be regard- ed as depending principally upon the amount of olefiant gas (heavy carburetted hydrogen) which it contains, the bulk of other gases being carriers rather than light-producers. The ole- fiant gas is separated by ignition into marsh gas (light carburetted hydrogen) and carbon, the solid particles of which become incandescent and emit white light, which is observed in the luminous cone of a gas flame, and which has the same constitution as that of a candle. (See FLAME.) Of the impurities, tar is separated in the hydraulic main and the condenser; ammonia in the hydraulic main, condenser, and washer; sulphuretted hydrogen, cyanogen, and carbonic acid in the washer and lime and iron purifier,