Imágenes de páginas

Art. IX. The Bakerian Lecture. On the Composition and

Analysis of the Inflammable Gaseous Compounds resulting from the Destructive Distillation of Coal and Oil ; with some Remarks on their relative Heating and Illuminating Powers. By W. T. BRANDE, Esq., Sec. R. S. Prof. Chem. R. I. From the Philosophical Transactions for 1820.

TT can hardly be laid to our charge, that a considerable period 1 has elapsed since any thing relating to Chemical inquiry has appeared in this Journal: For in fact, the labours of persons learned in that department of science, have lately furnished but little matter for speculation. The discoveries of Sir Humphry Davy-splendid in every sense of the word, and not less remarkable for the brilliancy than for the rapidity with which they were produced-have made us perhaps too un-. reasonable; and caused us to form an estimate of the labours of those who have succeeded him, less favourable than they really deserve. We have been spoilt by plenty ;-and because every year does not give birth to some great discovery, we exclaim that there is a famine in the land. Although Mr Brande, who succeeded Sir H. Davy in the Royal Institution, has been less successful than his great predecessor in the path of discovery, his researches, and, above all, his skill in analytical operations, have done much for Chemistry in general; and we willinglý take this opportunity of bearing witness to the utility of labours which-however great their excellence and intrinsic value may be-are too apt to be passed over without due estimation, because they happen to be wanting in originality and invention.

The paper before us contains some observations and experiments made on the inflammable gases used for the purposes of illumination. The inquiry was undertaken, in the first instance, with a view of ascertaining the mixture and quality of the gases best suited for such purposes; and as some novelties relative to the constitution of the gaseous compounds presented themselves in the course of the investigation, Mr Brande conceived the matter to be of sufficient importance to form the subject of the Bakerian Lecture.

When pit-coal is distilled, and the products collected in proper vessels, they are found to contain, besides other substances, a highly elastic fluid, which was long supposed to consist of two gases, compounds of carbon and hydrogen ;-the one called the heavy hydrocarburet, or olefiant gas, the other,' light hydrocarburet., The first of these is composed of equal portions of carbon and hydrogen ; the second, of one portion of Vol. XXXIV. No. 68.


cause the too iper great thearing

carbon and two of hydrogen. Now, if we take hydrogen to be 251, the specific gravity of the heavy, or olefiant gas, is 13.4, and that of light hydrocarburet is 77, or as .57363, assuming atmospheric air for unity. Upon examining the mixed coal gas, Mr Brande found its specific gravity as low as .4430. This gas he had obtained from the Gas-light Company's works at Westminster; but being aware that the density of this gas is various, according to the coal from which it is made, he prepared some at the laboratory of the Royal Institution, and the heaviest he met with was only.4940. He concluded then, that if coal gas were wholly composed of the two varieties of carburetted hydrogen, the specific gravity of the light hydrocarburet must have been estimated too high. To ascertain this, he procured some from acetate of potash, separated its carbonic acid by lime water, anı found its specific gravity to be .687. It was thierefore evident that the whole constituents of coal gas could not be the two hydrocarburets. Neither could a part of the mixture be the gaseous oxide of carbon, (which, according to Sir H. Davy is given out by coals in burning, and therefore might be introduced in the gas evolved during the distillation), because its specific gravity is .9834. Hence Mr Brande conjectured that coal gas must be a mixture of olefiant and hydrogen gases; and the experiments detailed in this paper are intended to confirm this opinion.

After detonating 100 measures of coal gas with 200 of oxygen by means of the electric spark over mercury, and absorbing the carbonic acid by liquid potassa, 36 measures of pure oxygen were found to remain in the tube. Hence 164 parts of oxygen were required for the complete combustion of 100 parts of coal gas. Now, 100 parts of olefiant gas require 300 of oxygen, and 100 of hydrogen 50, for their respective combustions ; * so that, if we suppose 100 parts of coal gas to be composed of 45 of olefiant, and 55 of hydrogen, the quantity of oxygen required for its perfect combustion will be very nearly 164 parts, and the mixture thus formed will have nearly the same specific gravity as the coal gas.

* See Henry's Elements of Chemistry, Vol. I. p. 355. Where he also states that it requires 190 volumes of oxygen for the perfect combustion of 100 of coal gas. The difference between this result and that stated by Mr Brande, must be owing to the different qualities of the coal gases under examination. Yet the proportions of oxygen necessary for the saturation of 100 measures of olefiant and hydrogen gases, mentioned in Mr Brande's paper, are precisely the same as those given by Henry. We presume Mr Brande bas offered them as the results of his own experiments.

Before noticing the next step in Mr Brande's inquiry, we must advert to an experiment of Berthollet, by which the de. composition of olefiant gas is effected in a very simple and beautiful manner. This is performed by passing the gas repeatedly through a tube heated to a very high temperature. In repeating the experiment, Mr Brande introduced 100 measures of olefiant gas-obtained by distilling alcohol and concentrated sulphuric acid-into a mercurial gasometer, connected with a second gasometer by means of a platinum tube, in which were placed some small crystals of quartz, previously heated to redness, for the purpose of increasing the heated surface over which the gas was to be passed. The tube was then heated to a very high degree of temperature, and the gas passed froin one gasoa meter to the other, until it ceased to dilate. The apparatus was then allowed to cool, and the volume of gas was found to be exactly doubled. This was detonated with an equal volume of oxygen, and the remainder proved to be half the volume of pure oxygen; showing that the olefiant gas had been reduced by this simple process of decomposition, into double its bulk of hydrogen. It also appeared that it had almost entirely parted with its carbon ; for the oxygen which remained, scarcely rendered lime water turbid, and was not apparently diminished by exposure to liquid potassa. In the heated part of the tube there was a considerable deposition of charcoal.

The apparatus remaining the same, 100 measures of coal gas were introduced into the gasometer, and underwent the same process. When cool, the gas was examined, and found to have increased 40 parts. It burned with a lambent flame, like hydrogen; and, when detonated over mercury, required very little more than half its volume of oxygen to render the combustion complete. Very little carbonic acid could be detected ; and, as in the former experiment, the inside of the platinum tube was lined with charcoal. It appears, from this, very evident that, as the quantity of olefiant gas contained in the coal gas is measured by the increase in bulk, after the gas has undergone decomposition by heat; therefore, the 100 measures of coal gas contained 40 of olefiant gas; and if no foreigri gases were present, the remaining 60 measures were hydrogen.

Upon the same principle, similar conclusions are drawn from another experiment, in which a glass tube containing a little sulphur and 100 measures of coal gas, is subjected to a red heat until the gas suffers no further dilatation. The volume, when cold, is found to have increased to 140 measures. Hence, if this increase is caused by the olefiant gas being changed by decomposition into double its bulk of hydrogen, it plainly fola lows, as in the last experiment, that the 100 measures of coal gas contained 40 of olefiant gas, and 60 of hydrogen.


Mr Brande found chlorine a very useful agent in analyzing the various compounds containing hydrocarburet. If chlorine and hydrogen are mixed together over water, and exposed to the action of common daylight, but kept out of sunshine, the gases do not act upon one another; and in the course of twenty-four hours, the chlorine will be found to be absorbed by the water, while the hydrogen remains. But if chlorine be mixed with olefiant gas, in the proportion of about three parts of chlorine to one of olefiant, and exposed to the action of daylight, the olefiant, if very pure, will be almost wholly absorbed. From this singular property of chlorine, it may be of great use in the analysis of any mixture of hydrogen hydrocarburet, carbonic oxide, and carbonic acid : for the carbonic acid may be absorbed by a solution of potassa. The remaining mixture being then united with thrice or four times its volume of pure chlorine, and exposed over water to daylight, the carburetted hydrogen, and any overplus of chlorine, will be absorbed: The remaining gas, consisting of hydrogen and carbonic oxide, may be mixed with oxygen, and detonated by the electric spark over mercury. The proportion of oxygen destroyed in the combustion being doubled, will give the hydrogen which was contained in the mixture; and the carbonic acid formed, will exactly measure the quantity of the carbonic oxide. The whole of this mode of analysis depends upon keeping the gas from the action of the solar rays, as it is only the absence of this agency that prevents a combination from taking place between the chlorine and the gases that compose the mixture.

We may mention here, by the way, a very curious effect produced by the action of electric light upon a mixture of chlorine and hydrogen. A tube containing the mixed gases was placed in a darkened room, within an inch of the charcoal points attached to the positive and negative wires of a very powerful Voltaic battery, highly charged. Upon making the circuit complete, the fumes of muriatic vapour were instantly produced; and in consequence of the production of muriatic acid, the water rose in the tube, and very soon the whole of the mixture was absorbed : the gases, too, exploded the moment they were affected by the electric light. These phenomena are similar to those observed in the combination which is produced between chlorine and hydrogen by the action of solar rays. And as the same effects have never yet been produced by the application of any other artificial light, it may fairly be concluded, that this singular agency of light in promoting chemical combination,

[ocr errors][merged small][merged small][merged small]
[ocr errors]

is peculiar to solar and electric rays. Mr Brande was induced to make this experiment, from having failed to produce the slightest effect upon the gases above mentioned, by any flame that could be engendered from the combustion of olefiant gasalthough the light of an argand burner, which he concentrated by means of a lens, produced a heat which raised the mercury in a thermometer placed in the focus, 4°.5 in five minutes. To return to our subject.

Most of the experiments we have detailed were performed upon the gas procured from the decomposition of whale oil. This gas is much heavier than that obtained by the distillation of coal. Its specific gravity is .7690; and 100 cubical inches weigh upwards of 23 grains. Now, 100 cubical inches of ole. fiant gas weigh 30.15 grains, and 100 of hydrogen 2.25 grains. Hence, if oil gas consist of these gases only, they will be nearly in the proportion of three volumes of olefiant to one of hydrogen. From these experiments Mr Brande concludes, that olefiant gas is the only definite compound of carbon and hydrogen; and that the various inflammable compounds produced by distillation from coal, oil, &c. consist essentially of a mixture of olefiant and hydrogen gases. We admit that this has so far been established; although we might object to the tentative methods which Mr Brande has employed to confirm his conjectures, (pp. 18, 19, 20). A straight forward process would certainly have been preferable; and we are at a loss to understand how he should have omitted to state the result of a method which cannot possibly have escaped him, and which might, more than any other, have strengthened his hypothesis. We allude to the direct analysis of coal or oil gas, by subjecting them to the action of chlorine. By means of this, the olefiant gas being absorbed, the remaining part of the mixture might have been accurately ascertained, both as to quality and quantity. If discovered to be pure hydrogen, the inquiry is at once put at rest; and if mixed with any foreign gases, the presence of such might : easily have been detected, either by detonation with oxygen, or by other methods. At all events, it would have been satisfactory to know what such an experiment produced. We are far from explaining Mr Brande's silence on this subject, by supposing that the trial did not prove satisfactory to his hypothesis ; and yet it is difficult to conceive how it should not have been made.

We must also take leave to observe, that in some parts of his inquiry, Mr Brande's train of reasoning is a little fallacious. It is very like what mathematicians call, arguing in a circle. For example; he conjectures, from the specific gravity of oil gas, that it is composed of one volume of hydrogen and three of ole,

« AnteriorContinuar »