SCIENTIFIC.

Otago Witness, Issue 1974, 19 September 1889, Page 35

SCIENTIFIC.

WATER GAS. WHAT IT IS, AND HOW IT IS MADE.

The uses of water gas and its accompanying products in the great furnace industries of the country are now so considerable, and are multiplying so rapidly, as to excite not a little interest in their future possible applications. The outlook for a new and cheap gas illuminant which should be free from the many disadvantages of coal gas is considered to have been distinctly improved by recent improvements in water gas manufacture, although there are still difficulties in the way of its adoption for general household purposes. Apart from the question of economy, which is a leading aim in the .new enterprise, such an illuminant would in many ways be an enormous benefit to those who at present have to breathe the air in which coal gas is burnt, with its sulphurous and other deleterious products. It must be remembered that each oubic foot of coal gas requires 5*20 cubic feet of air to burn in ; but water gas is content with 2"20 cubic feet, thus leaving so much the more for the human furnace to consume. Another advantage of water gas is that no free carbon is produced ; hence there is no smoke to blacken walls and ceilings and pollute the air. From a purely hygienic standpoint, therefore, water gas can claim a much higher place in the list of illuminants than coal gas. It may help our readers to an insight into the possibilities of the future, or at least the conditions under which the problem is being worked- out, if we give them an elementary description of the chemistry of water gas, and a short account of a water gas works in its latest form with all the newest appliances on which so much of the future of gas-lighting may depend.

In the manipulation of water gas no new scientific principle is involved; no greater theoretical knowledge of chemistry is required than any schoolboy of 14 who goes up for his Cambridge " Local " possesses. In a single sentence, the theory of water gas manufacture is that when steam is passed over burning fuel it forms with such fuel carbonic acid and hydrogen; the carbonic acid coming into contaot with more coke at i higher temperature is converted into carbonic oxide, and forms a mechanical mixture with hydrogen.

Now for a few words about the process of manufacture itself. The first object to attract the notice of the visitor to a water gas works is the " generator," which is very similar in external appearance to a miniature blast furnace. It is a cylindrical vessel of boiler plate, lined with fire brick, and standing about 16ft in height. At the base there is an ordinary furnace, but provided with a water-cooled ring forming the " throat," in which is a stream of water, aSj the heat here is very intense. Over the furnace the cylinder is filled with a column of coke, with which the generator is fed from a platform that surmounts the whole apparatus. When the furnace is well alight, what is known as the " blowing-up " takes place, by means of which the lower portion of the coke is raised to an intense incandescence. The necessary draught of air is obtained by a steam-jet exhauster, which sucks in air at the bottom through the column of fuel, discharging the resulting products of combustion by a chimney into the atmosphere. This operation is carried on for about 10 minutes, by which time the lower portion of the fuel is in a roaring state of incandescence. Tbe workman in charge then turns a handwheel, by means of which a system of valves is reversed, the steam being shut off from the exhauster and directed into the top of the generator. The hot carbon by affinity instantly seizes upon the oxygen, producing carbonic acid. This travelling through another stratum of hot fuel becomes broken up into oxygen and carbonic oxide, which latter is identical with the blue flame often seen on a bright red fire. As the hydrogen of the steam remains unchanged the final result of the decomposition is a mixture of hydrogen and carbonic oxide — i.e., " water gas."

Thus produced, the water gas passes out of the generator into the " scrubber." There it is cooled in contact with water trickling over coke. It thence passes into an ordinary gasholder. Water gas passes through purifiers after it has been stored in the gasholder. An important reason for this lies in the fact that as the gas is produced very rapidly it has not time, in passing from the generator to the gasholder, to become properly cleansed. The purifiers are similar in structure to those used in ordinary gasworks, but an oxide of iron is usually used in the place of lime, there being little carbonic acid to be removed from water gas.

It should be understood that water gas by itself possesses no illuminating power, but gives a non-luminous flame of a light-blue colour. To use water gas as an illuminating agent, advantage is taken of the fact that its flame is 2772deg Fahr. hotter than the hottest flame of coal gas. Over the almost non-luminous flame is inserted a comb consisting of calcined magnesia (not magnesium, as has been erroneously stated). This is rendered incandescent and emits a brilliant, white light, almost as intense as an electric incandescent lamp, but far more agreeable, as the illuminating surface is much larger, and consequently there is less irritation to the retina. These " combs " must be changed every hundred hours (they cost l£d each), as it is found that they gradually diminish in their power of incandescence. If five cubic feet of gas are being burned per hour, the comb gives at first a photometric power of 20 candles, after 50 hours it gives but 15-candle light, and after 100 hours only 10. Fortune seems to have favoured the inventor by presenting him at this point with a curious anomaly. Although the actual heat of the flame is so great, very little is radiated, indeed the hand can be held quite near the flame without inconvenience. This is probably due to the high absorptive powers of calcined magnesia.

It may have occurred to some that the time daring which the coke in the generator is being raised to incandescence is so much time lost. But this is not the case, for a gas — " producer " gas — may then be formed which is in fact used with great advantage for heating purposes. Its formation is doe to chemical combination between the air of the blast and the coke, and it consists of a mixture of carbonic oxide, marsh gas, hydrogen, nitrogen, and carbonic acid — a composi-

less dangerous and much more economical for heating purposes than coal gas. . " Producer" gas may be conducted away by a special outlet, and stored in a special gasometer.

By this means 150,000 cubic feet of heafeing gas may be obtained from a ton of coal, or 15 times as much a3 coal gas. The enormous rapidity with which water gas ia evolved is greatly in its favour, gmounting as it does in some cases to no less than 20,000 cubic feet per hour. The distorted shapes of some of the pieces of incombustible residue lying near the generator tell how fierce the process of. decomposition must be. All this must naturally react upon the pocket of the maker; and, as a matter of fact, where both varieties of gas are made — water gas and " producer" gas— the cost is a little under per 1000 cubic fee&. The producer gas is already used for the following out of a long list of manufactures: steel melting, tin annealing, alkali production, phosphorus distilling, plate glass making, nickel roasting, oil and tar distilling, and brick burning.

A word or two may be added in conclusion as to the sanitary effect of the adoption of water gas. Coal gas burnt in rooms impregnates the air with (among other compounds) sulphuric acid derived from those sulphur compounds from which it is impossible to free the gas. In the case of water gas the only products of combustion are water gas and carbonic acid. Although the latter is injurious to health, it should be remembered that whereas a cubic foot of coal gas requires 5*2 cubic feet of air to support its combustion, 2422 4 2 cubic feet of air suffices for water gas, thus leaving three cubic feet of extra air to feed the human flame.

The solution of one of the greatest town problems of modern times — the prevention of the pall of smoke and smoke fog which increasingly poisons and darkens the air in our industrial and commercial centres — • seems also bound up with the question of the gas whose chemistry and manufacture we have here briefly sketched. — " Leisure Hour."