The aëriform compounds of hydrogen and carbon, which were already entitled to accurate investigation, as objects of scientific research, have derived an additional claim to the attention of the chemist, from their application to an important economical purpose, described in a late communication to the Royal Society. Yet there is, perhaps, no part of chemistry, the investigation of which is beset with greater difficulty, or with more numerous sources of error ; insomuch, that the actual state of the science enables us to attain scarcely more than approximations to the truth, and degrees of probability of greater or less amount. It was the object of the experiments, which are described in the following pages, rather to remove some of the obstacles, which present themselves to a successful enquiry into the nature of these bodies, than to acquire such facts, as may enable the chemical philosopher to decide the controverted question respecting their composition. Results, sufficiently multiplied and precise for this purpose, would require a larger appropriation of time, than I have the prospect of being able to bestow; and I can only on the present occasion, offer an example of the method, in which it appears to me that the analysis of this class of substances will be most successfully attempted. When a vegetable substance, composed (as may be assumed to simplify the statement) of oxygen, hydrogen, and carbon, united in the form of a ternary compound, is submitted to distillation, at a temperature not below that of ignition, the equilibrium of affinities, which constituted the triple combination, is destroyed ; and the elements, composing it, are united in a new manner. Those, which are disposed to enter into permanently elastic combinations, escape in the state of gas. The carbon, uniting with oxygen, either composes carbonic acid gas, or, stopping short of that degree of oxygenation, which is essential to change it into an acid, is converted into carbonic oxide. The hydrogen, combining with a portion of carbon, constitutes a binary compound of those two ingredients, forming either what has been called carbureted hydrogen gas , or supercarbureted , better known by the appellation of olefiant gas. Towards the close of the process, a portion of simple hydrogen gas is also mingled with the products. Perhaps in no instance is any one of the gases, which have been enumerated, obtained perfectly pure, by the distillation of a vegetable substance. The aeriform fluids, which are thus generated, are found to be possessed of almost every degree of specific gravity ; and to yield, by combustion, extremely different results, according to the temperature at which they have been formed ; the stage of the process at which they have been separated; and other modifying circumstances. It becomes an interesting question, whether these gases, so much diversified in their physical and chemical properties, are mixtures of a few binary compounds, with which chemists are already acquainted; or whether, on the contrary, their elements are capable of uniting in indefinite proportions, and of composing ternary compounds of oxygen, hydrogen, and carbon, or varieties of oxy-carbureted hydrogen. It would encroach too much on the time of the Royal Society, to enter upon this controversy. And, as neither opinion admits, at present, of demonstrative evidence, I may be permitted, in explaining the following experiments, to assume that theory, which appears to me most probable; viz. that the aeriform products of the distillation of vegetable substances, are mixtures of carbonic acid, carbonic oxide, olefiant, carbureted hydrogen, and simple hydrogen gases; or of two or more of these in various proportions.