we find no difficulty, either physical or metaphysical. He persuades us to go, leads us and describes all to us in a few sentences, when volumes of persuasion written before had not been sufficient to induce men to turn their eyes. His descriptions are rigid as well as picturesque. Some persons would apply to them the word material, and still more the word mechanical. It was by following rigidly the mechanical properties of his atoms that he arrived at his results. To those who read his works, it will be clear that his mind became gradually more confirmed in this course. In reading what he says, at p. 49, we see him plainly verging towards his theory, and also the nature of his struggle, which is in no respect similar to that of any other inquirer. He there first says, that he is inquiring into the relative weights of the ultimate particles of bodies. This idea had never suggested itself as practical to any one before Dalton, nor am I aware that it has ever been claimed. Having made some advance in this inquiry, he made it the starting point of all that he advanced on atomic chemistry and the theory of proportion. He was not in haste to publish his theory, but told it openly to Dr. Thomson, in 1804; this, then, is the date of the complete discovery, as Dr. Thomson published an abstract of it at once. Some persons unacquainted with this have advanced an argument against him, his own book containing the subject not having been published till 1808. A well known quotation from Dr. Thomson's history says, "Mr. Dalton informed me that the atomic theory first occurred to him during his investigations of olefiant gas and carburetted hydrogen gas, at that time imperfectly understood, and the constitution of which was first fully developed by Mr. Dalton himself. It was obvious from the experiments which he made upon them, that the constituents of both were carbon and hydrogen, and nothing else. He found, further, that if we reckon the carbon in each the same, then carburetted hydrogen contains exactly twice as much hydrogen as olefiant gas does. This determined him to state the ratios of these constituents in numbers, and to consider the olefiant gas a compound of one atom of carbon and one atom of hydrogen; and carburetted hydrogen of one atom of carbon and two atoms of hydrogen. The idea thus conceived was applied to carbonic oxide, water, ammonia, &c., and numbers were given representing the atomic weights of oxygen, azote, &c., deduced from the best analytical experiments which chemistry then possessed." * * 66 His first atomic weights, already given,* were published in 1803; he did not publish his "New System" till 1808. He says then, "A pure elastic fluid is one, the constituent particles of which are all alike, or in no way distinguishable. These fluids are constituted of particles possessing very diffuse atmospheres of heat, the capacity or bulk of the atmosphere being often one or two thousand times that of the particle in a liquid or solid form. Whatever, therefore, may be the shape or figure of the solid atom abstractedly, when surrounded by such an atom it must be globular; but as all the globules in any small given volume are subject to the same pressure, they must be equal in bulk, and will, therefore, be arranged in horizontal strata like a pile of shot." The chapter "On Chemical Synthesis" gives his theory. He there says, "When any body exists in the elastic state, its ultimate particles are separated from each other to a much greater distance than in any other state; each particle occupies the centre of a comparatively large sphere, and supports its dignity by keeping all the rest, which, by their gravity, or otherwise, are disposed to encroach on it, at a respectful distance. When we attempt to conceive the number of particles in an atmosphere, it is somewhat like attempting to conceive the number of stars in the universe; we are confounded with the thought. But if we limit the subject, by taking a given volume of any gas, we seem persuaded that, let the divisions be ever so minute, the number of particles must be finite; just "A New System of Chemical Philosophy." Part I., p. 145. * Page 49. as in a given space of the universe, the number of stars and planets cannot be infinite." "Chemical analysis and synthesis go no farther than to the separation of particles one from another, and to their reunion. No new creation or destruction of matter is within the reach of chemical agency. We might as well attempt to introduce a new planet into the solar system, or to annihilate one already in existence, as to create or destroy a particle of hydrogen. All the changes we can produce consist in separating particles that are in a state of cohesion or combination, and joining those that were previously at a distance. "In all chemical investigations it has justly been considered an important object to ascertain the relative weights of the simples which constitute a compound. But unfortunately the inquiry has terminated here; whereas from the relative weights in the mass, the relative weights of the ultimate particles or atoms of the bodies might have been inferred, from which their number and weight in various other compounds would appear, in order to assist and to guide future investigations and to correct their results. Now it is one great object of this work to shew the importance and advantage of ascertaining the relative weights of the ultimate particles, both of simple and compound bodies, the number of simple elementary particles which constitute one compound particle, and the number of less compound particles which enter into the formation of one more compound particle. "If there are two bodies A and B which are disposed to combine, the following is the order in which the combinations may take place, beginning with the most simple: namely, 1 atom of A+1 atom of B-1 3 atoms of A+1 atom of B=1 atom of C, binary. "The following general rules may be adopted as guides in all our investigations respecting chemical synthesis. "1st. When only one combination of two bodies can be obtained, it must be presumed to be a binary one, unless some cause appear to the contrary. "2nd. When two combinations are observed, they must be presumed to be a binary and ternary. "3rd. When three combinations are obtained, we may expect one to be a binary, and the other two ternary. "4th. When four combinations are observed, we should expect one binary, two ternary, and one quaternary, &c. "5th. A binary compound should always be specifically heavier than the mere mixture of its two ingredients. "6th. A ternary compound should be specifically heavier than the mixture of a binary and a simple, which would, if combined, constitute it, &c. 7th. The above rules and observations equally apply when two bodies such as C and D, D and E, &c., are combined." * * * "In the sequel the facts and experiments from which these conclusions are derived will be detailed, as well as a great variety of others, from which are inferred the constitution and weight of the ultimate particles of the principal acids, the alkalis, the earths, the metals, the metallic oxides and sulphurets, the long train of neutral salts, and in short, all the chemical compounds which have hitherto obtained a tolerably good analysis. Several of the conclusions will be supported by original experiments. "From the novelty as well as importance of the ideas suggested in this chapter, it is deemed expedient to give plates exhibiting the mode of combination in some of the more simple cases. A specimen of these accompanies this first part. The elements or atoms of such bodies as are conceived at present to be simple, are denoted by a small circle, with some distinctive mark; and the combinations consist in the juxtaposition of two or more of these; when three or more particles of elastic fluids are combined together in one, it is to be supposed that the particles of the same kind repel each other, and therefore take their stations accordingly." In the figures to which he refers above he has shewn to us how vividly he formed these ideas, that they were no mere fancies which had passed through his brain, but distinct impressions, ready prepared for utterance. No doubt is left upon our minds as to his opinions, which are, that every piece of matter, even the smallest, must follow the laws of the largest; that when pounds of matter unite, the atoms contained in them must unite also, until we come to the fact that only atoms can really be said to unite. Now as the conception of any fraction of an atom is a contradiction and impossible, they must constantly unite as wholes, and the proportion will be constant. If constant in the smallest quantities, then so in the largest, explaining the permanency of the constitution of bodies so much disputed, and making it a law of nature. If two compound bodies unite, the same law is followed out. He then gives instances of combination, and adds to his explanation a plate of the "arbitrary marks or signs chosen to represent the several chemical elements or ultimate particles.” He gives twenty atomic weights and seventeen analyses of gases and acids. His atomic weights are |
