Accustomed as we are at the present day to see street after street of well-lighted thoroughfares, brilliantly illuminated by gas-lamps maintained by public authority, we can scarcely appreciate the fact that the use of gas is, comparatively speaking, of but recent growth, and that, like the use of coal itself, it has not yet existed a century in public favour. Valuable as coal is in very many different ways, perhaps next in value to its actual use as fuel, ranks the use of the immediate product of its distillation—viz., gas; and although gas is in some respects waning before the march of the electric light in our day, yet, even as gas at no time has altogether superseded old-fashioned oil, so we need not anticipate a time when gas in turn will be likely to be superseded by the electric light, there being many uses to which the one may be put, to which the latter would be altogether inapplicable; for, in the words of Dr Siemens, assuming the cost of electric light to be practically the same as gas, the preference for one or other would in each application be decided upon grounds of relative convenience, but gas-lighting would hold its own as the poor man's friend. Gas is an institution of the utmost value to the artisan; it requires hardly any attention, is supplied upon regulated terms, and gives, with what should be a cheerful light, a genial warmth, which often saves the lighting of a fire.
The revolution which gas has made in the appearance of the streets, where formerly the only illumination was that provided by each householder, who, according to his means, hung out a more or less efficient lantern, and consequently a more or less smoky one, cannot fail also to have brought about a revolution in the social aspects of the streets, and therefore is worthy to be ranked as a social reforming agent; and some slight knowledge of the process of its manufacture, such as it is here proposed to give, should be in the possession of every educated individual. Yet the subjects which must be dealt with in this chapter are so numerous and of such general interest, that we shall be unable to enter more than superficially into any one part of the whole, but shall strive to give a clear and comprehensive view, which shall satisfy the inquirer who is not a specialist.
The credit of the first attempt at utilising the gaseous product of coal for illumination appears to be due to Murdock, an engineer at Redruth, who, in 1792, introduced it into his house and offices, and who, ten years afterwards, as the result of numerous experiments which he made with a view to its utilisation, made a public display at Birmingham on the occasion of the Peace of Amiens, in 1802.
More than a century before, however, the gas obtained from coal had been experimented upon by a Dr Clayton, who, about 1690, conceived the idea of heating coal until its gaseous constituents were forced out of it. He described how he obtained steam first of all, then a black oil, and finally a "spirit," as our ancestors were wont to term the gas. This, to his surprise, ignited on a light being applied to it, and he considerably amused his friends with the wonders of this inflammatory spirit. For a century afterwards it remained in its early condition, a chemical wonder, a thing to be amused with; but it required the true genius and energy of Murdock to show the great things of which it was capable.
London received its first instalment of gas in 1807, and during the next few years its use became more and more extended, houses and streets rapidly receiving supplies in quick succession. It was not, however, till about the year 1820 that its use throughout the country became at all general, St James' Park being gas-lit in the succeeding year. This is not yet eighty years ago, and amongst the many wonderful things which have sprung up during the present century, perhaps we may place in the foremost rank for actual utility, the gas extracted from coal, conveyed as it is through miles upon miles of underground pipes into the very homes of the people, and constituting now almost as much a necessity of a comfortable existence as water itself.
The use of gas thus rapidly extended for illuminating purposes, and to a very great extent superseded the old-fashioned means of illumination.
[Illustration: FIG. 34.—Inside a Gas-Holder.]
The gas companies which sprang up were not slow to notice that, seeing the gas was supplied by meter, it was to their pecuniary advantage "to give merely the prescribed illuminating power, and to discourage the invention of economical burners, in order that the consumption might reach a maximum. The application of gas for heating purposes had not been encouraged, and was still made difficult in consequence of the objectionable practice of reducing the pressure in the mains during daytime to the lowest possible point consistent with prevention of atmospheric indraught."
The introduction of an important rival into the field in the shape of the electric light has now given a powerful impetus to the invention and introduction of effective gas-lamps, and amongst inventors of recent years no name is, perhaps, in this respect so well known as the name of Sugg. As long as gas retained almost the monopoly, there was no incentive to the gas companies to produce an effective light cheaply; but now that the question of the relative cheapness of gas and electricity is being actively discussed, the gas companies, true to the instinct of self-preservation, seem determined to show what can be done when gas is consumed in a scientific manner.
In order to understand how best a burner should be constructed in order that the gas that is burnt should give the greatest possible amount of illumination, let us consider for a moment the composition of the gas flame. It consists of three parts, (1) an interior dark space, in which the elements of the gas are in an unconsumed state; (2) an inner ring around the former, whence the greatest amount of light is obtained, and in which are numerous particles of carbon at a white heat, each awaiting a supply of oxygen in order to bring about combustion; and (3) an outer ring of blue flame in which complete combustion has taken place, and from which the largest amount of heat is evolved.