It would lead us too far to enter into minute details concerning the structure, uses and arrangement of the various apparatus employed in the production of gas; it will suffice to observe that when coal is heated to redness in a close vessel, it yields a variety of products which may be classed under three heads, as,--1st, permanent gases; 2ndly, vapours condensable into the liquid or solid state by cooling; and 3rdly, the residuary matter, coke, which remains in the retort. The object of gas manufacture is to separate these from each other, and to purify the gaseous products by washing and other means, so as to render them fit for combustion. The following particulars, taken from Brande’s Dictionary of Science, may serve to give an idea of the quantity of gas annually consumed in London. The oldest of the London gas-works is the establishment belonging to the original chartered company. They have three stations; the largest situated in Peter-street, Westminster; the second in Brick-lane, St. Luke’s, and the third in the Curtain-road, Shoreditch. This company consumes 50,000 chaldrons of coals annually, the produce of which in gas may be estimated at about six hundred million cubic feet, or about eighteen million seven hundred and fifty thousand pounds _weight_ of gas. It may be assumed that each chaldron of coals weighs 2880 lbs., and yields an average produce of 12,000 cubic feet of purified gas. The prime cost of gas is about four or five shillings per 1000 cubic feet; the usual retail price is from seven to ten shillings per 1000 cubic feet. The chartered company probably supplies about a fifth part of the whole of the gas consumed in London and the suburbs; so that the total annual consumption of coal employed for this important manufacture in the London district only, probably exceeds two hundred and fifty thousand chaldrons, and the quantity of gas produced for the supply of this district amounts annually to three thousand million cubic feet. The _weight_ of this quantity of gas exceeds seventy-five millions of pounds; and the _light_ produced by its combustion may be considered as equivalent to that which would be obtained by the combustion of one hundred and sixty millions of pounds of mould-candles of six to the pound. The operations of the London Gas-light Company, which was established in the year 1833, are also on a scale of great magnitude. Their works, situated at Vauxhall, are not only the most powerful, but the most complete in arrangement of any in the world. From this point their mains ramify to a prodigious extent in Middlesex as well as Surrey, and by the admirable mode in which they are laid, aided by the power of their works, they are enabled to supply gas at Highgate Hill (seven miles distance) with the same precision and in the same abundance as at Vauxhall. The extent of their pipes exceeds one hundred and fifty miles.