to suspect that the proportions of the principles are not the same in every specimen of the elastic fluid which we consider as fixable air. When the dense inflammable air first expelled from charcoal was used, the result was nearly the same. And from the whole, I conclude, that when as much inflammable air of this kind is employed, as can be converted in the explosion, by the empyreal air, the fixable air consists of one part by weight of the acid matter of acetous acid or charcoal, and nearly, or accurately, two parts of empyreal air; and almost one-fifth of this kind of inflammable air is phlogiston, and the remainder mere acid basis of fixable air, and of acetous acid, charcoal, oils, spirits, and of all substances that yield acetous acid or dense inflammable air abundantly."*

The same remarks apply to this. The "nearly" two parts are just as probable, in his mind, as the "accurately" two parts, which would not have been the case had he found any defining law to express on the subject.

Then he says, further on,t "It seems, therefore, that the proportions in which the acid and phlogistic matter are combined, in different specimens of inflammable air expelled from vegetable substances, do vary considerably," &c. This refers to his tables of results.

He believes that the particles of the different gases unite to form molecules of compound gases, page 317: "I consider the specific gravity as a safe guide in our investigation of these affinities and of their order, in regard only to the elastic fluids which seem to consist of no more than one kind of gravitating matter engaged in the repellent atmospheres; and of fixed air, dense inflammable air, acid air, the phlogistic alkaline air, and others, I would observe, that the atmospheres include molecules, instead of solitary ultimate parts; for, without this chemical union of heterogeneal parts, and the formation of molecules, an elastic fluid of the kind that I now speak of could not differ, as it does, from either kind of matter * Page 291. † Page 294.

of which it is composed. From this consideration of the attractive forces which tend to form molecules, and of the atmospheres which, in compound elastic fluids, encompass the molecules, but not the ultimate parts severally, we derive an easy explanation of the phenomenon so often noted in the preceding pages-I mean, the conversion of a substance, not into air, but into two or three different elastic fluids, by mere ignition."

Dr. Higgins thinks of atoms, of simple particles, and even speaks of gases uniting, in some cases, in nearly, if not accurately, a fixed proportion, and yet he sees no law. He does not carry his idea far enough. If the molecules are formed by the union of two particles the proportions must of necessity be fixed, or if any number of particles unite, the proportions are fixed, unless the molecules are to be supposed of different constitutions. In this last case, they would constitute a mixture of different gases. But it was not known at this period that all bodies had a fixed constitution, otherwise one would have supposed that Dalton's laws would have been readily arrived at by Dr. Higgins. On the other hand, his theory was not clear, or he would have been led by it to decide on the necessity of fixed constitution as a result. But we obtain no results affecting chemical philosophy. And yet amongst other questions which he says "we shall find no difficulty in answering," is, "Why does any excessive quantity of empyreal or of inflammable air, beyond the determinate proportions in which their gross parts can combine, remain elastic and unaltered, or not altered in any considerable part of it, after the combustion ?" *

The nearest answer he gives as to the proportions is the following:-"The matter of fire limits the quantity in which aeriform fluids, and bodies containing it, can combine chemically." We may conclude then that nothing in the gases themselves determined the proportion, but the cause was in "distinct atmosphere of fiery matter."

In reading the first part of this question we suppose he must live as a discoverer; in reading the second part, we find him timidly committing suicide. He wavers between his theory and his experiments. If determinate proportion be a law, he might have supposed it rigid, like other laws of nature; but he leaves a portion of the residue altered, so that, after all, we only receive from him indeterminate, or nearly determinate proportions.

The experiment to which the question refers occurs in p. 296. He draws no valuable conclusion from it. He says also, p. 299, "In the combustion of charcoal with empyreal air, the expenditure of the latter, in fixable air and water, was always found to be more than thrice the weight of the charcoal. I could now easily ascertain the proportion of these, and even the quantity of the acid and phlogistic matter in this and other bodies; but as my present purposes are answered by approximation, I think it unnecessary to detain the reader any longer on this subject."

His principal object was to explain the nature of fire, which he considers as subject to the laws of gravitation, and to be the cause of the aeriform state of bodies.

"The

The only law in which be introduces numbers is the fourth of his "primary notions of the matter of fire." changes of repellent matter, by which attractive and gravitating particles form elastic fluids, are distinct atmospheres of fiery matter, in which the densities are reciprocally as the distances from the central particles, in a duplicate or higher ratio." *

His writings are mostly in the first stage of thought before opinion is formed. Commentators on such persons are obliged to extend the ideas a little in order to make them clear, and so the original writer gets credit for more than he had ever done. Such writers are of great value when they lead towards discoveries; but we are apt to give them the entire honour when

they deserve only a part. As far as our subject is concerned Dr. Higgins has small claims. His opinions on atoms might have been held by the ancients: whilst standing on their shoulders, it would have required much less sagacity to discover than was needed for them. He speaks of the sums of the forces of atoms measuring the attraction of matter, but does not suppose that if matter be atomic, the number of atoms might also, in this way, be got comparatively.

We might say, however, that Dr. Higgins began the study of atomic chemistry, properly so called, although he made little advance in it.

The next person worthy of note is of the same name and family. The following extracts contain what is of greatest importance in connection with our subject. The title page of the volume quoted from is, "A Comparative View of the Phlogistic and Antiphlogistic Theories, with Inductions, &c., by William Higgins, of Pembroke College, Oxford. The Second Edition.

"Est quoddam prodire tenus, si non datur ultra. "London: Printed for J. Murray, No. 32, Fleet Street. 1791." The first edition was in 1789.

Page 14. "It is generally allowed, and justly, that nitrous air consists of dephlogisticated air and phlogistic, in the proportion of two of the former to one of the latter. The supposition of its containing phlogiston, I hope, will hereafter appear to be erroneous; therefore, every ultimate particle of phlogisticated air must be united to two of dephlogisticated air; and these molicules, combined with fire, constitute nitrous air. Now, if every (one) of these molicules were surrounded with an atmosphere of fire equal in size only to those of dephlogisticated air, 100 cubic inches of nitrous air should weigh 98,535 grains; whereas, according to Kirwan, they weigh but 37 grains. Hence, we may justly conclude that the gravitating particles of nitrous air are thrice the distance from each other that the ultimate particles of dephlogisticated

are in the same temperature, and, of course, their atmospheres of fire must be in size proportionable; or else some other repelling fluid must interpose. The size of the repelling atmospheres of nitrous air thus considered, and likewise the weaker attraction of the molicules of this air to dephlogisticated air than that of the ultimate particles of phlogistic in their simple state, it is surprising to me, with how much more facility the former unites to dephlogisticated air than the latter."

After speaking of the combustion of sulphur, he says, p.35, "A good many more facts might be urged on this subject; but, in my opinion, enough has been adduced to convince an impartial reader that all the phenomema above recited are only explicable by entirely leaving out phlogiston, and supposing sulphur to be a simple subtance, whose ultimate particles attract dephlogisticated air with forces inherent in themselves, independent of phlogiston or concrete inflammable air, as an alkali does an acid, or gold and tin mercury; and likewise supposing the combustion of sulphur to be as simple a process as that of light inflammable air; that is, that there is no dephlogistication, or formation of water, during the union of the oxygenous principle to sulphur, as containing not a particle of light inflammable air in its constitution. I have often combined sulphur rendered perfectly dry, and dephlogisticated air likewise, deprived of its water by fused marine selenite in large proportion over mercury, and could never observe that water was produced. Indeed it may be said that the volatile sulphurous acid, which is always the result of this process, may redissolve it; but this is not very likely, when a small portion of water will deprive it of its elasticity."

According to Mr. Kirwan, 100 grains of sulphur require 143 grains of dephlogisticated air to convert them into volatile vitriolic acid; but they require much more in order to become perfect vitriolic acid. Highly concentrated vitriolic acid contains two parts of dephlogisticated air, and one of