and interesting facts relating to the progress of Gas-lighting in the metropolis, which exhibit, in a striking point of view, the rapid and extensive advances it was then making. He stated that at the three stations belonging to the Chartered Gas Company, twenty-five chaldron of coal were daily carbonized, producing 300,000 cubic feet of gas, which was equal to the supply of 75,000 Argand lamps, each yielding the light of six candles. At the City Gas Works, in Dorset Street, Blackfriars, the quantity of coal daily carbonized amounted to three chaldron, which afforded a quantity of gas adequate to the supply of 1500 Argand lamps; so that twenty-eight chaldron of coal were daily carbonized at that time, and 76,500 lights supplied by those two companies only.*

The subject which at this time seems to have excited the greatest degree of public interest was coal gas; and although Mr. Clegg had distinguished himself by his various admirable contrivances, his were not the only attempts, for there were many other candidates for fame in the same branch of art. The period was, indeed, prolific in schemes for its improvement, and several persons obtained patents for their respective plans. But its purification was the object which principally occupied attention; and, though essentially

* Journal of the Royal Institution, Vol. I. page 71,

important, had certainly proved the most difficult to effect. It is true that the chemical principles which regulated the operation were well known, but to discover the best mechanical means of their effective and economical application to large quantities of gas, appears to have been the purpose of the greater number of the inventions. Some of them not only evinced ingenuity, but also proved to be useful, and are therefore deserving of notice; besides, they exhibit, in a favourable point of view, the zealous and laudable efforts of various individuals for improving the art of Gas-lighting.

One of the first of these plans, which is remarkable, was that devised by Mr. D. Wilson, of Dublin, who, in 1817, took out a patent for purifying coal gas by means of the chemical action of ammoniacal gas.* His process consisted in mixing the two gases together as they were produced, and then passing the mixture through a large vessel containing water. The ammoniacal gas was generated from lime, saturated with ammoniacal

* This patent is dated March 1, 1817, and the specification and drawings will be found in the Repertory of Arts, Vol. XXXII. page 11. Mr. J. F. Ledsam, of Birmingham, has recently obtained a patent for purifying coal gas by a similar process; and he states that his plan effects his purposes most completely, and is practised to a considerable extent at the Birmingham and Staffordshire Gas Works.

liquor, which was afterwards distilled in a separate apparatus, and collected in a vessel, placed directly over the brick-work containing the fireplace where its distillation was carried on. The connexion between this vessel and the retorts was formed by means of a large pipe which entered at the top and descended under a perforated shelf, to occasion the coal gas to diffuse itself, so as more completely to mix with the other. As this combination of the sulphuretted hydrogen with the ammoniacal gas rendered the mixture soluble, it was dissolved in its passage through the water, and the carburetted hydrogen gas was rendered pure before it entered the gasometer to pass to the burners. Though this method proved efficacious for its purposes to a certain extent, it appears to have been attended with some inconveniences or difficulties, and was therefore never much introduced into practice.

Another plan to purify coal gas was devised by Mr. Reuben Phillips, of Exeter, who, in the same year, obtained a patent for the purification of coal gas by the use of dry lime.* In his process the lime was first slacked and finely sifted, when a sufficient quantity of water was added to render

* Mr. Phillips's patent is dated July 19, 1817. The Repertory of Arts contains the plan and drawings of the apparatus: Vol. XXXIII. page 67.

it moist, so that its particles would slightly adhere together. The vessels that contained the lime might be ranged in a circle or otherwise, as circumstances rendered desirable or necessary, and five or more were to be employed according to the extent of the works. The connexion between the several vessels was formed by means of pipes, which entered at their tops; each vessel was fitted with one or two moveable shelves, perforated with a great number of holes; and the lime was placed on these shelves in a layer of about six inches thick. The gas entered by a pipe at the bottom of the vessels, and had to force its passage through the lime in order to escape at the top to go into the adjoining vessel, and thus it passed through the whole series before it could arrive at the gasholder. The vessels were constructed without bottoms, and stood in a cistern containing water or some other fluid, about six inches deep, so as to prevent any escape of the gas, and any one of them could be removed without interfering with the operation. This method was found to be efficient for its object, and is still practised at some places.

In the succeeding year, Mr. G. Holworthy Palmer took out a patent* for a method of puri

* The date of Mr. Palmer's patent is January 15, 1818. Repertory of Arts, Vol. XXXIV. page 196.

fying coal gas, which differed very materially from any of the preceding plans. Previously to the gas being exposed to this process it was thoroughly condensed, that the tar and ammonia might be completely separated from it; and when it was thus partially purified, the gas was passed through iron retorts heated to a dark red. These retorts were required to be more than half filled with various oxidizeable substances, such as iron clippings or turnings, or iron ore, the black oxide of iron, or others of a similar nature; and very particular attention was also necessary with respect to the temperature. To deprive the gas of the sulphuretted hydrogen and carbonic acid seems to have been the primary purpose of this mode of purification; but the patentee had also in view another object, which was certainly very important, and that was, to obviate the nuisance arising from the lime, when saturated with the sulphuretted hydrogen; for this occasioned much vexation on several accounts, and particularly from its unpleasant odour annoying those who lived in the vicinity of gas works. But some disadvantages were connected with the operation, and one of considerable moment; for if the retorts were heated to too high a temperature, the circumstance produced a deposition of carbon, and therefore diminished the illuminating power of the gas. This of course would operate