It is the contact of the body to be heated with the flame before combustion is complete which gives rise to the greatest mischief; any cooling of the flame extinguishes a portion of the flame, and the gases present in the flame at the moment of extinction creep along the cooled surface and escape combustion.
Dr. Blochmann has shown the composition of the gases in various parts of the Bunsen flame to be as follows:
| Height above tube. | In tube. | 1 inch. | 2 inch. | 3 inch. | Complete |
| Air with 100 vols. gas | 253.9 | 284.7 | 284.5 | 484.3 | 608.8 |
| Hydrogen | 48.6 | 36.4 | 17.7 | 16.1 | Nil. |
| Marsh gas | 39.0 | 40.1 | 28.0 | 5.7 | Nil. |
| Carbon monoxide | 2.9 | 2.2 | 19.9 | 12.7 | Nil. |
| Olefiant gas | 4.0 | 3.4 | 2.2 | Nil. | Nil. |
| Buteylene | 3.0 | 2.5 | 1.6 | Nil. | Nil. |
| Oxygen | 52.7 | 52.0 | 21.7 | Nil. | Nil. |
| Nitrogen | 199.1 | 223.8 | 225.9 | 382.4 | 482.3 |
| Carbon dioxide | 0.8 | 3.5 | 13.0 | 41.7 | 62.4 |
| Water vapor | 3.1 | 11.8 | 45.8 | 116.1 | 141.2 |
Which results show that it would be impossible to check the flame anywhere short of the extreme tip (where complete combustion is approximately taking place), without liberating deleterious products. I think I have said enough to show that no gas stove, geyser or gas cooking stove should be used without ample and thorough means of ventilation being provided, and no trace of the products of combustion should be allowed to escape into the air; until this is done, the use of improper forms of stoves will continue to inflict serious injury on the health of the people using them, and this will gradually result in the abandonment of gas as a fuel, instead of, as should be the case, its coming into general use. The English householder is far too prone to accept what is offered to him, without using his own common sense, and will buy the article which tickles his eye the most and his pocket the least, on the bare assurance of the shopkeeper, who is only anxious to sell; but when he finds that health and comfort are in jeopardy, and has discarded the gas stove, it will take years of labor to convince him that it was the misuse of gas which caused the trouble. Already signs are not wanting that the employers of gas stoves are beginning to fight shy of them, and I earnestly hope that the gas managers of the kingdom will bring pressure to bear upon the stove manufacturers to give proper attention to this all important question.
So strongly do I feel the importance of this question to the gas world and the public, that I freely offer to analyze the products of combustion given off by any gas stove or water heater sent to me at Greenwich during the next six months, on one condition, and that is that the results, good, bad, or indifferent, will be published in a paper before this Society, which has always been in the front when matters of great sanitary importance to the public had to be taken up. And if after that the public like to buy forms of apparatus which have not been certified, it is their own fault; but I do think that the maker of any stove or geyser which causes a death should be put upon his trial for manslaughter.
In conclusion, let us consider for a moment what is likely to be the future of gas during the next half century. The labor troubles, bad as they are and have been, will not cease for many a weary year. The victims of imperfect education (more dangerous than none at all, as, while destroying natural instinct, it leaves nothing in its place) will still listen and be led by the baneful influence of irresponsible demagogues, who care for naught so long as they can read their own inflammatory utterances in the local press, and gain a temporary notoriety at the expense of the poor fools whose cause they profess to serve. The natural tendency of this will be that every labor-saving contrivance that can will be pressed into the gas manager's service; and that, although coal (of a poorer class than at present used) will still be employed as a source of gas, the present retort setting will quickly give way to inclined retorts on the Coze principle; while, instead of the present wasteful method of quenching the red hot coke, it will be shot direct into the generator of the water gas plant, and the water gas carbureted with the benzene hydrocarbons derived from the smoke of the blast furnace and coke oven, or from the creosote oil of the tar distiller, by the process foreshadowed in the concluding sentences of my last lecture. It will then be mixed with the gas from the retorts, and will supply a far higher illuminant than we at present possess. In parts of the United Kingdom, such as South Wales, where gas coal is dear, and anthracite and bastard coals are cheap, water gas highly carbureted will entirely supplant coal gas, with a saving of fifty per cent. on the prices now existing in those districts. While these changes have been going on, and while improved methods of manufacture have been tending to the cheapening of gas, it will have been steadily growing in public favor as a fuel; and if in years to come the generation of electricity should have been so cheapened as to allow it to successfully compete with gas as an illuminant, the gas works will still be found as busy as of yore, the holder of gas shares as contented as to-day; for with a desire for a purer atmosphere and a white mist instead of a yellow fog, gas will have largely supplanted coal as a fuel, and gas stoves, properly ventilated and free from the reproaches I have hurled at them to-night, will burn a gas far higher in its heating power, far better in its power of bearing illuminating hydrocarbons, and free from poisonous constituents.
When the demand for it arises, hydrogen gas can be made as cheaply as water gas itself, and when time is ripe for a fuel gas for use in the house, it is hydrogen and not water gas which will form its basis. With carbureted water gas and 20 per cent. of carbon monoxide we are still below the limit of danger, but a pure water gas with over 40 per cent. of the same insidious element of danger will never be tolerated in our households. Already a patent has been taken by Messrs. Crookes and Ricarde-Seaver for purifying water gas from carbon monoxide, and converting it mainly into hydrogen by passing it at a high temperature through a mixture of lime and soda lime, a process which is chemically perfect, as the most expensive portion of the material used could be recovered; but in the present state of the labor market it is not practical, as for the making of every 100,000 cubic feet of gas, fifteen tons of material would have to be handled, the cost of labor alone being sufficient to prevent its being adopted; moreover, hydrogen can be made far cheaper directly.
From the earliest days of gas making, the manufacture of hydrogen by the passage of steam over red-hot iron has been over and over again mooted, and attempted on a large scale, but several factors have combined to render it futile.
In the first place, for every 478.5 cubic feet of hydrogen made under perfect theoretical conditions never likely to be obtained in practice, 56 lb. of iron were converted into the magnetic oxide, and as there was no ready sale for this article, this alone would prevent its being used as a cheap source of hydrogen; the next point was that when steam was passed over the red-hot iron, the temperature was so rapidly lowered that the generation of gas could only go on for a very short period, while, finally, the swelling of the mass in the retort and fusion of some of the magnetic oxide into the side renders the removal of the spent material almost an impossibility. These difficulties can, however, be got over. Take a fire clay retort, six feet long and a foot in diameter, and cap it with a casting bearing two outlet tubes closed by screw valves, while a similar tube leads from the bottom of the retort. Inclose this retort by a furnace chamber of iron lined with fire brick, leaving a space of two feet six inches round the retort, and connect the top of the furnace chamber with one opening at the top of the upright retort, while air blasts lead into the bottom of the furnace chamber, below rocking fire bars, which start at bottom of the retort, and slope upward, to leave room for ash holes closed by gas tight covers. The retort is filled with iron or steel borings, alone if pure hydrogen is required, or cast into balls with pitch if a little carbon monoxide is not a drawback, as in foundry work. The furnace chamber is now filled with coke, fed in through manholes, or hoppers, in the top, and the fuel being ignited, the blast is turned on, and the mixture of nitrogen and carbon monoxide passes over the iron, heating it to a red heat, while the fuel in contact with the retort does the same thing.
When the fuel and retort full of iron are at a cherry-red heat, the air blast is cut off, and the pipe connecting the furnace and retort, together with the pipe in connection with the bottom of the retort, are closed, and steam, superheated by passing through a pipe led round the retort or interior wall of the furnace, is injected at the bottom of the red-hot mass of iron, which decomposes it, forming magnetic oxide of iron and hydrogen, which escapes by the second tube at the top of the retort, and is led away either to a carbureting chamber if required for illumination, or direct to the gasholder if wanted as a fuel. The mass of incandescent fuel in the furnace chamber, surrounding the retort, keeping up the temperature of retort and iron sufficiently long to enable the decomposition to be completed.