Meanwhile, we may just consider how we ought to deal with solid fuel, whether for the purpose of making gas from it or for burning it in situ. The question arises, In what form ought solid fuel to be - ought it to be in lumps or in powder? Universal practice says lumps, but some theoretical considerations would have suggested powder. Remember, combustion is a chemical action, and when a chemist wishes to act on a solid easily, he always pulverizes it as a first step.
Is it not possible that compacting small coal into lumps is a wrong operation, and that we ought rather to think of breaking big coal down into slack? The idea was suggested to me by Sir W. Thomson in a chance conversation, and it struck me at once as a brilliant one. The amount of coal wasted by being in the form of slack is very great. Thousands of tons are never raised from the pits because the price is too low to pay for the raising - in some places it is only 1s. 6d. a ton. Mr. McMillan calculates that 130,000 tons of breeze, or powdered coke, is produced every year by the Gas Light and Coke Company alone, and its price is 3s. a ton at the works, or 5s. delivered.
The low price and refuse character of small coal is, of course, owing to the fact that no ordinary furnace can burn it. But picture to yourself a blast of hot air into which powdered coal is sifted from above like ground coffee, or like chaff in a thrashing mill, and see how rapidly and completely it might burn. Fine dust in a flour mill is so combustible as to be explosive and dangerous, and Mr. Galloway has shown that many colliery explosions are due not to the presence of gas so much as the presence of fine coal-dust suspended in the air. If only fine enough, then such dust is eminently combustible, and a blast containing it might become a veritable sheet of flame. (Blow lycopodium through a flame.) Feed the coal into a sort of coffee-mill, there let it be ground and carried forward by a blast to the furnace where it is to be burned. If the thing would work at all, almost any kind of refuse fuel could be burned - sawdust, tan, cinder heaps, organic rubbish of all kinds. The only condition is that it be fine enough.
Attempts in this direction have been made by Mr. T.R. Crampton, by Messrs. Whelpley and Storer, and by Mr. G.K. Stephenson; but a difficulty has presented itself which seems at present to be insuperable, that the slag fluxes the walls of the furnace, and at that high temperature destroys them. If it be feasible to keep the flame out of contact with solid surfaces, however, perhaps even this difficulty can be overcome.
Some success in blast burning of dust fuel has been attained in the more commonplace method of the blacksmith's forge, and a boiler furnace is arranged at Messrs. Donkin's works at Bermondsey on this principle. A pressure of about half an inch of water is produced by a fan and used to drive air through the bars into a chimney draw of another half-inch. The fire bars are protected from the high temperatures by having blades which dip into water, and so keep fairly cool. A totally different method of burning dust fuel by smouldering is attained in M. Ferret's low temperature furnace by exposing the fuel in a series of broad, shallow trays to a gentle draught of air. The fuel is fed into the top of such a furnace, and either by raking or by shaking it descends occasionally, stage by stage, till it arrives at the bottom, where it is utterly inorganic and mere refuse. A beautiful earthworm economy of the last dregs of combustible matter in any kind of refuse can thus be attained. Such methods of combustion as this, though valuable, are plainly of limited application; but for the great bulk of fuel consumption some gas-making process must be looked to.
No crude combustion of solid fuel can give ultimate perfection.
Coal tar products, though not so expensive as they were some time back, are still too valuable entirely to waste, and the importance of exceedingly cheap and fertilizing manure in the reclamation of waste lands and the improvement of soil is a question likely to become of most supreme importance in this overcrowded island. Indeed, if we are to believe the social philosophers, the naturally fertile lands of the earth may before long become insufficient for the needs of the human race; and posterity may then be largely dependent for their daily bread upon the fertilizing essences of the stored-up plants of the carboniferous epoch, just as we are largely dependent on the stored-up sunlight of that period for our light, our warmth, and our power. They will not then burn crude coal, therefore. They will carefully distill it - extract its valuable juices - and will supply for combustion only its carbureted hydrogen and its carbon in some gaseous or finely divided form.
Gaseous fuel is more manageable in every way than solid fuel, and is far more easily and reliably conveyed from place to place. Dr. Siemens, you remember, expected that coal would not even be raised, but turned into gas in the pits, to rise by its own buoyancy to be burnt on the surface wherever wanted. And not only will the useful products be first removed and saved, its sulphur will be removed too; not because it is valuable, but because its product of combustion is a poisonous nuisance. Depend upon it, the cities of the future will not allow people to turn sulphurous acid wholesale into the air, there to oxidize and become oil of vitriol. Even if it entails a slight strain upon the purse they will, I hope, be wise enough to prefer it to the more serious strain upon their lungs. We forbid sulphur as much as possible in our lighting gas, because we find it is deleterious in our rooms. But what is London but one huge room packed with over four millions of inhabitants? The air of a city is limited, fearfully limited, and we allow all this horrible stuff to be belched out of hundreds of thousands of chimneys all day long.
Get up and see London at four or five in the morning, and compare it with four or five in the afternoon; the contrast is painful. A city might be delightful, but you make it loathsome; not only by smoke, indeed, but still greatly by smoke. When no one is about, then the air is almost pure; have it well fouled before you rise to enjoy it. Where no one lives, the breeze of heaven still blows; where human life is thickest, there it is not fit to live. Is it not an anomaly, is it not farcical? What term is strong enough to stigmatize such suicidal folly? But we will not be in earnest, and our rulers will talk, and our lives will go on and go out, and next century will be soon upon us, and here is a reform gigantic, ready to our hands, easy to accomplish, really easy to accomplish if the right heads and vigorous means were devoted to it. Surely something will be done.
The following references may be found useful in seeking for more detailed information: Report of the Smoke Abatement Committee for 1882, by Chandler Roberts and D.K. Clark. "How to Use Gas," by F.T. Bond; Sanitary Association, Gloucester. "Recovery of Volatile Constituents of Coal," by T.B. Lightfoot; Journal Society of Arts, May, 1883. "Manufacture of Gas from Oil," by H.E. Armstrong; Journal Society of Chemical Industry, September, 1884. "Coking Coal," by H.E. Armstrong; Iron and Steel Institute, 1885. "Modified Siemens Producer," by John Head; Iron and Steel Institute, 1885. "Utilization of Dust Fuel," by W.G. McMillan; Journal Society of Arts, April. 1886. "Gas Producers," by Rowan; Proc. Inst. C.E., January, 1886. "Regenerative Furnaces with Radiation," and "On Producers," by F. Siemens; Journal Soc. Chem. Industry, July, 1885, and November, 1885. "Fireplace Construction," by Pridgin Teale; the Builder, February, 1886. "On Dissociation Temperatures," by Frederick Siemens; Royal Institution, May 7, 1886.Second of two lectures delivered at the Royal Institution, London, on 17th April, 1886. Continued from SUPPLEMENT, No. 585, p. 9340.
Near Colorados, in the Argentine Republic, a large bed of superior coal has been opened, and to the west of the Province of Buenos Ayres extensive borax deposits have been discovered.