as one reason against its adoption; but perhaps the complicated construction of the apparatus, and the nice attention it required, as well as economical considerations, might all combine to prevent its extensive use, whatever might be the peculiar advantages which in some respects the plan seemed to present.

A method of purifying coal gas, by means of passing it through heated tubes, was also suggested, about the same time, by Mr. Samuel Parker,* of Liverpool. He did not employ any oxidizeable substances, but he passed the crude gas through an arrangement of three iron pipes placed horizontally in a furnace, and they were connected together by a gun-barrel. He found the quantity of gas exceeded that obtained in the usual way, that the proportion of tar was considerably less, and that the gas also was perfectly pure. The fluid, which was collected in a vessel interposed between the extremity of the ignited iron pipes through which the gas passed and the gasometer, contained no vestige of ammonia; but, on the contrary, it instantly reddened litmus paper, was acid to the taste, and its odour was pungently sulphureous. Its colour was black, and, when largely diluted, produced an insoluble precipitate with muriate of barytes. Mr. George

Mr. Parker communicated his method in a letter to the Philosophical Magazine, Vol. LII. p. 292.

Lowe, of Derby, also purified coal gas by conveying it through an iron cylinder containing iron turnings, &c., after which he stated that it might be passed through lime-water, or not, at pleasure. He conceived that the increase of gas noticed by Mr. Parker, arose from the decomposition of the water, and not the tar, to which Mr. Parker attributed it.*

Although the purification of gas might be the principal object, it was not the only branch of the art which occupied the attention of those who were interested in the subject. Various schemes were suggested for economically effecting the greater as well as the more ready production of gas, by the arrangement and setting of the retorts, so that several might be regularly heated at one time. In 1817, Mr. Perks, of the City of London Gas Works, obtained a patent for a contrivance of this kind, and his plan consisted in placing twelve retorts in a circle with one in the centre of them, so that the whole thirteen could be

* Mr. Lowe's plan is in Philosophical Magazine, Vol. LII. p. 371; and he states that he made his discovery whilst he was constructing a stove for the purpose of giving light and heat, which he called a Thermophotogen. In Vol. LIII. p. 262, he also gave a delineation and description of a very simple apparatus which he had constructed out of an eighteen-gallon beer cask, with various fittings for purifying coal gas with cream of lime. He also contrived a condenser with a similar vessel.

heated at once. In fact, imagination was actively engaged in devising schemes which had the same purposes in view, and the number proposed to be set and heated together differed from two to seven, or more. Opinion also equally varied with respect to the forms most eligible in the construction of retorts-and circular, semi-circular, elliptic, square, as well as others, were deemed preferable, according to the judgment or fancy of the different operators. But these variations occasioned many experiments to be made to ascertain the respective utility of each, and these were often productive of considerable expense as well as disappointment. Perhaps each form and mode had advantages in particular circumstances, but long experience has not produced uniformity of opinion on this subject, for at different places the forms and practice too are different.

Among the variety of plans which appeared was that of Mr. John Grafton, who had been a pupil of Mr. Clegg's. He obtained a patent for some improvements in the construction of gas apparatus, and a part of his scheme consisted in constructing retorts which were open at both ends and lined with fire-clay. He adopted a method of placing them in an inclined position;

The date of Mr. Grafton's patent is Dec. 10, 1818; Repertory of Arts, Vol. XXXVIII. p. 272.

and he had also a secondary retort to receive the tar, that it might be re-distilled and converted into gas. In fact, the abundant production of this substance from the distillation of the coal rendered the discovery of an eligible and effective method of decomposing it, a very desirable object to attain, so as to prevent its too large accumulation, from the difficulty of disposing of it in that form. The process was certainly successful to a certain extent, but although the plan displayed ingenuity in the contrivance, the results of its operations have not proved so advantageous as its inventor anticipated. However, the failure of such attempts is perhaps rather to be attributed to physical causes than to any deficiency of ability or skill employed in them.

Mr. Cawood, of Leeds, also communicated, through the medium of the public journals, a useful plan for setting retorts, and its principal feature was placing them in such a manner that they might be uniformly heated by the regular circulation of flame over their whole external surfaces.*

*

Probably the circumstance was unknown to Mr. Cawood, but this method of heating retorts had been long practised in many of the processes employed in the manufactories of Birmingham and Sheffield. Indeed, it is the plan which had been generally used for heating the muffles

In fact, the various schemes and suggestions for the improvement of Gas-lighting, which appeared in the different scientific and other journals of that period, evinced the great interest cherished for its successful establishment; and that which had alternately been a subject of ridicule, alarm, or reprobation, had now innumerable advocates, who seemed emulous to outvie each other in their endeavours to recommend its use, to ameliorate its processes, or to obviate any objections or inconveniences that might obstruct its employment as a preferable means to afford light.

CHAPTER XI.

CIRCUMSTANCES RELATIVE TO THE INTRODUCTION OF OIL GAS. MR. JOHN TAYLOR OBTAINS A PATENT FOR HIS APPARATUS, AND ERECTS ONE OF THEM AT APOTHECARIES' HALL, &C.

Having pursued coal gas through all its vicissitudes from the earliest accounts of its disco

for assaying gold and silver, as well as for soldering, and a variety of other purposes, as described in Lewis's Philosophical Commerce of the Arts.