Part 6 (1/2)

flame of the blow-pipe, since this part, if turned upon an oxide, will reduce it, ie, abstract its oxygen from it This part also corresponds with the jet of the Bunsen burner, when the holes are closed by which otherwise air would as-stove when the gas ignites beneath the proper igniting-jets, and which gives consequently a white or yellow flame

The third portion, on the other hand, corresponds with the ”oxidising”

flaen to bodies that are thirsting for it This also corresponds with the ordinary blue flaas-stoves where heat, and not light, is required, the blue fla caused by the adas ive the best illumination, we must increase the yellohite space of carbon particles at a white heat, and a burner that will do this, and at the same time hold the balance so that unconsumed particles of carbon shall not escape in the way of s results With this end in view the addition of albo-carbon to a bulb in the gas-pipe has proved very successful, and the incandescent gas-jet is constructed on exactly the saht about this desirable end has doubtless not been without effect in acting as a powerful obstacle to the widespread introduction of the electric light

Without entering into details of the lance at the principal parts of the apparatus used

The gasometer, as it has erroneously been called, is a faht but unfortunately also to the organs of sas-holder, in which the final product of distillation of the coal is stored, and fro mains

The first, and perhaps,is the series of _retorts_ into which the coal is placed, and from which, by the application of heat, the various volatile products distil over These retorts are huge cast-iron vessels, encased in strong brick-work, usually five in a group, and beneath which a large furnace is kept going until the process is complete Each retort has an iron exit pipe affixed to it, through which the gases generated by the furnace are carried off The exit pipes all empty the horizontal cylinder, and in this the gas begins to deposit a portion of its impurities The ias, tar, ammoniacal liquor, sulphur in various for left behind in the retort In the hydraulic in to be deposited The gas passes on to the _condenser_, which consists of a number of U-shaped pipes Here the impurities are still further condensed out, and are collected in the _tar-pit_ whilst the gas proceeds, still further lightened of its ias in the condenser is reduced to about 60 F, but below this soas would commence to be deposited in liquid for of temperature A mechanical contrivance known as the _exhauster_ is next used, by which the gas is, as, helped forward in its onward as then passes to the _washers_ or _scrubbers_, a series of tall towers, from which water is allowed to fall as a fine spray, and by e quantities of aen, carbonic acid and oxide, and cyanogen compounds, are re the coke, hich it is filled, damp, absorbs these compounds, and the union of the a in the for salts), sulphide and sulphocyanide of a Retorts by Machinery]

[Illustration: FIG 36--CONDENSERS]

Hitherto the purification of the gas has been brought about by as now enters the ”_purifier_,” in which it undergoes a further cleansing, but this time by cheent used is either lias is robbed of its carbonic acid and the greater part of its sulphur coas passes on into the water chaas-holder is reared, and in which it rises through the water, forcing the huge cylinder upward according to the pressure it exerts

The gas-holder is poised between a nuht pillars by a series of chains and pulleys, which allow of its easy ascent or descent according as the supply is greater or less than that drawn froas mains

[Illustration: FIG 38]

When we see the process which is necessary in order to obtain pure gas, we begin to appreciate to what an extent the atmosphere is fouled when many of the products of distillation, which, as far as the production of gas is concerned, may be called impurities, are allowed to escape free without let or hindrance In these days of strict sanitary inspection it seeas-works is still allowed to become contaminated by the escape of i apparatus Go where one may, the presence of these compounds is at once apparent to the nostrils within a none too limited area around them, and yet their deleterious effects can be alents, and by a scientific oversight of the whole apparatus It certainly behoves all sanitary authorities to look well after any gas-works situated within their districts

Now let us see what these first five products of distillation actually are

Firstly, house-gas Everybody knohat house-gas is It cannot, however, be stated to be any one gas in particular, since it is a ases, and often contains se proportion consists of what is known as en This occurs occluded or locked up in the pores of the coal, and often oozes out into the galleries of coal-mines, where it is known as firedaetable matter has fallen and has becoether with an admixture of ten times its volume of air, a miniature coal-mine explosion could be produced by the introduction of a match into the mixture Alone, however, it burns with a feebly lureat portion of its heating power Marsh-gas is the first of the series of hydro-carbons known cheht substance, being little ht of an equal bulk of air It is coen to one of carbon (CH_{4})

Marsh-gas, together with hydrogen and the monoxide of carbon, the last of which burns with the dull blue flame often seen at the surface of fires, particularly coke and charcoal fires, foras, and are none of the power of house-gas depends on the presence therein of olefiant gas (_ethylene_), or, as it is soen This is the first of the series of hydro-carbons known as the _olefines_, and is coen (C_{2}H_{4}) Others of the olefines are present inthe illureatly enhanced, too, by the presence of a small quantity of benzene vapour These illuminants, however, constitute but about 6 per cent of the whole

Added to these, there are four other usual constituents which in no way increase the value of gas, but which rather detract from it They are consequently as far as possible re These are nitrogen, carbonic acid gas, and the destructive sulphur coen and carbon bisulphide vapour It is to the last two to which are to be attributed the injurious effects which the burning of gas has upon pictures, books, and also the tarnishi+ng which ive rise to the for incessantly poured into the air Of course the aiven off is little as compared with that which escapes from a coal fire, but, fortunately for the inoes up the chi the evil day, until the atmosphere becomes so laden with impurities that what proceeds at first up the chih the doors and s A recent official report tells us that, in the town, of St Helen's alone, sufficient sulphur escapes annually into the atmosphere to finally produce 110,580 tons of sulphuric acid, and a computation has been ed annually with 180 tons of the sa acid It is acontinues to exist in such places at all

The chief constituents of coal-gas are, therefore, briefly as follows:--

/ (1) Hydrogen, | (2) Marsh-gas (carburetted hydrogen or fire-daas (ethylene, or heavy carburetted hydrogen), with other olefines, / (5) Nitrogen, | (6) Carbonic acid gas, | (7) Sulphuretted hydrogen, (8) Carbon bisulphide (vapour),

the last four being regarded as impurities, which are removed as far as possible in the manufacture

In the process of distillation of the coal, we have seen that various other iht into existence The final residue of coke, which is inated with the sulphur which has not been volatilised in the forases, we need scarcely as-tar and the ammoniacal liquor are two i as engineers as unfortunately necessary nuisances in the as, they have both become so valuable on account of as itself to be sold now at less than half its original price The waste of for utilised in this, and an instance is recorded in which tar, which was known to have been lying useless at the bottoineer for distilling purposes It has been estimated that about 590,000 tons of coal-tar are distilled annually

Tar in its primitive condition has been used, as every one is aware, for painting or tarring a variety of objects, such as barges and palings, in fact, as a kind of protection to the object covered froes of insects or worms, or to prevent corrosion when applied to metal piers

But it is worthy of a better purpose, and is capable of yielding far inative individual could have dreao

In the process of distillation, the tar, after standing in tanks for some time, in order that any ammoniacal liquor which may be present e stills, where a moderate amount of heat is applied to it The result is that some of the more volatile products pass over and are collected in a receiver These first products are known as _first light oils_, or _crude coal-naphtha_, and to this naphtha all the numerous natural naphthas which have been discovered in various portions of the world, and to which have been applied numerous local names, bear a very close resemblance Such an one, for instance, was that ss, in Derbyshi+re, fro--obtained his well-known paraffin oil, which gave the initial impetus to what has since developed into a trade of ilobe