must be deemed interesting from the information it displays with every part of the subject of discussion, whether it relate to its scientific principles or its practical details. Indeed, the improvement of gas-lighting had long been the object of his ardent pursuit; and as he had been the earliest to point out the incorrect and delusive representations of the peculiar advantages of oil gas, his evidence excited curiosity, because it was the result of acute observation, from the varied opportunities afforded him by extensive experience. He was therefore interrogated on this occasion more rigidly and minutely than any other person, and began by stating that he had been conversant with the nature of coal gas for eight years, about five of them on a small scale at Derby, but for the last three or four on the largest possible, as the superintendant at two of the Chartered Company's stations, viz. Brick Lane and Curtain Road.

In the year 1819, the inhabitants of Derby (of which he was a native) contemplated the lighting of their town with gas; and several of them who were likely to take the lead in its management, requested him to visit London, with the view of making himself acquainted with the state of the science of gas-lighting at that period. He visited all the coal-gas establishments in the metropolis, and also the manufactory of the Patent Appara

tus for Oil Gas, where every facility was given him by the Patentees for seeing Oil-Gas Apparatus in perfection. From his opportunities of observation, and the information he was enabled to obtain, he felt satisfied that oil gas would in no way compete, as to profit and general circumstances, with coal gas. He also visited Norwich at a subsequent period, where he had the best opportunities afforded him of witnessing the effects of oil-gas illumination; and, indeed, he had made every exertion to acquire all the information he could, which had any reference to the subject. He observed, that during the last two years he had made a number of experiments with the sole object of arriving at truth, and getting at the bottom of the long-contested point on the comparative advantages of oil and coal gas; that nine-tenths of those experiments had been made in the presence of Mr. Cooper, the chemist; some of them Dr. Fyffe had witnessed; and some, on the heating and lighting power, by Professor Leslie, who had gone over the whole apparatus.

The real composition of oil or coal gas, Mr. Lowe observed, as a chemical compound, is at present unknown; it is carbon and hydrogen in some combination or other; and he entertained very little doubt but that the illuminating power of both oil and coal gas will be found to consist of that peculiar compound of carbon and hydro

gen at present known as naphthaline.* For in making oil gas, this peculiar resplendent crystallization of the naphthaline was found, but whether these gases may turn out to be naphthaline in solution with hydrogen, or a definite compound of carbon and hydrogen, must yet be determined by the experiments of philosophers and chemists.

With respect to oil gas, he stated, that not only more carbon, but more hydrogen, entered into its composition; for though both contained olefiant gas, this latter was in the greater ratio in oil gas. It was well known that in the hydrogen and carbon forming olefiant gas, a condensation of volume takes place; two volumes of carbon with two of hydrogen, constituting one of olefiant gas; consequently that gas which possesses most olefiant gas, must contain more hydrogen, in equal volumes, though in a condensed state. As a proof that naphthaline exists to a

* By the great pressure which the Portable Gas Company apply to condense their gas, nearly a gallon of highly volatile oil is stated to be produced from the gas by the operation. Dr. Henry pointed out some of the properties of this fluid in his paper in the Phil. Trans. 1820; and Mr. Lowe also noticed it in his letter to the Phil. Mag., 1821, he stated it to possess the property of adding greatly to the illuminating power of the gas as well as to its specific gravity. Mr. Faraday gave an analysis of it in Phil. Transactions, 1825.

where

much greater extent in oil gas than in coal gas, he stated, that if any of the condensible products arising from the manufacture of oil gas were spilt upon a table, in a very few minutes the part will be covered over with brilliant crystals of naphthaline.*

The specific gravity of coal and oil gas being one of the criterions of their value, was a subject which occupied a good deal of attention, and Mr. Lowe remarked, that they were generally believed to be valuable in the ratio of their specific gravity; but that this property alone would not be a guide, for he had detected in oil gas from five to seven and a half per cent. of carbonic acid, which would add to its weight and lessen its illuminating power. The creation of carbonic acid depends very much upon the temperature at which the

is made, but exists both in coal and oil gas;

* Mr. Lowe described naphthaline to be a crystalline body, composed of hydrogen and carbon; the carbon being in a very high ratio, about 90 per cent., and as one of the most volatile of substances; completely disappearing at the temperature of 80. He stated that, according to the analysis of Dr. Ure, of Glasgow, this substance contains double the quantity of carbon to that existing in olefiant gas; that it is in fact a solid, consisting of the substances which constitute olefiant gas,—a combination of carbon and hydrogen, perhaps two volumes of olefiant gas, condensed into a solid.

he had found more of it in the former than in the latter, and the same means deprives both the gases of that substance.*

In the course of his evidence he detailed various experiments which he had made to ascertain the number of cubic feet of gas to be obtained from a gallon of oil at different temperatures, and also with a mixture of varied proportions of volatile oil. The result arising from the whole of his experiments was, that when oil gas was made of a high specific gravity, the condensible products would be excessive, and none of those must be returned into the retorts; that, generally, to make oil gas of the specific gravity of 750, a gallon of oil would produce about eighty cubic feet of gas; and that the oil gas given to the public was about 750, which he deemed a fair average. He knew of no method of converting volatile oil into gas without a great deposition of carbon; its chemical nature would not admit of it; the making of oil gas was a slow process, and had been tried on a large scale at Norwich and Colchester, where it proved to be far from profitable.

In some of his experiments he had a greater deposition of carbon than in others, and the rea

* Carbonic acid has the same specific gravity as oil gas, and is heavier by one half than atmospheric air.

+ See Appendix (I).