a series of important observations, entitled "Experimental Essays on the constitution of mixed gases," &c. He completely disproved the idea of vapour being held in the air by chemical affinity. He showed, also, that all elastic fluids expand equally by one degree of heat. This important law has often been called Gay-Lussac's, that distinguished chemist having published it a few months later, evidently having discovered it himself.
In Manchester, as formerly in Cumberland, meteorology was a favourite subject with Dalton. In his examination of the mode of analyzing air, he had discovered that when using nitric oxide to absorb the oxygen, it required seventy-two measures to absorb the oxygen of one hundred measures of air. If more were used, then some of the nitrous gas would be found as a residue; if less, then some of the oxygen gas would be found as a residue. This led him to conclude that "the elements of oxygen may combine with a certain portion of nitrous gas;" or, as another experiment showed, "with twice that portion, but with no intermediate portion." In the one case nitrous acid is produced; in the other, nitric acid. Dalton's papers, in 1803-4, on "The Diffusion of Gases, and the Absorption of Gases by Water and other Liquids," bring out prominently his mode of viewing these bodies as consisting of distinct particles. Uniting this with his theory of mixed gases, which he conceives do not rest on particles not of their own kind, we have Dalton's idea of a gas which he compares to a pile of shot, each shot supported by contact with the periphery of the shot below. If the gases be mixed, then the particles of oxygen will rest on those of oxygen, the particles of hydrogen on those of hydrogen. When a gas is pressing on water the results are complex; if there be no gas in the water, the pressure of the gas is entirely on the surface. Water absorbs 1-27th of its bulk of oxygen; in that case the oxygen gas standing on the surface of the water would press by 1-27th on the oxygen gas which is in the water, and the rest of its pressure, 26-27ths, would be on the surface of the water itself. In this case the stratum of gas above the water will press on the upper stratum of gas in the water with 1-27th of its weight. The distance of the two strata must be nearly twenty-seven times the distance of those in the gas above, and nine times the distance of the particles in the water. This arises from the outer or incumbent gas having a greater repulsive power than the inner, which has its repulsion removed by the water, and by its greater density, as it presents nine particles to one of the dissolved gas. In desiring to account for the establishment of an equilibrium between the inner and outer gas, he felt the greatest difficulty to be in the fact that different gases observed different laws—that water did not admit the same bulks of every gas. On this point he observes—"I am nearly persuaded that the circumstance depends upon the weight and number of the ultimate particles of the several gases," but he afterwards found this not very probable. He adds—"An inquiry into the relative weights of the ultimate particles of bodies is a subject, as far as I know, entirely new; I have been lately prosecuting this inquiry with remarkable success." He then gives his first crude table of atomic weights. No one had ever before ventured to weigh, even relatively, particles which have always been regarded rather in a metaphysical than a physical light.
These speculations excited a general curiosity respecting their author, both in his own country and on the continent. He was invited to lecture in London, Edinburgh, and other places. At this time he was about thirty-eight years of age. His labours were uninterrupted, except when, on Thursday afternoon, he played a game at bowls with some old friends. He was silent generally in large companies, but had a good deal of dry humour. When deep in the difficulty of bringing out the atomic theory, he sought repose at the house of the Rev. Mr. Johns. It was his substitute for a house of his own, as he "never had time" to marry. He was a simple inquirer into nature; his enthusiasm rose only in tier presence. Abstracted in a great measure from the world in its social relations, with the few persons who shared his friendship he was frank and affectionate to an extreme in all his behaviour. Gentle and kind in his disposition, but untutored in the arts of polished society, he was deeply loved by a small circle of intimate friends; but in the presence of strangers he was noted for a certain rigidity both of mind and body, which conveyed strongly the force, and altogether dissembled the graces of his character. He was simple, temperate, and regular in his habits; never carried away by the feelings of the moment. If he had a passion at all it was order, method, regularity.
This was the man who was to astonish the world with the atomic theory, one of the simplest conceptions in science, to some extent a necessary truth. Dalton said that if a pound of one material united with a pound of another, half a pound would unite with half a pound, and so on, down to the smallest existing parts. Now, when we come to the smallest parts, we cannot conceive that less than one can combine with another, because the atom is indivisible; but one may unite to two or two to three, or, in fact, any number of one kind may form groups with any number of another kind; but to make the same quality of groups, not only must the same combination be made, but the smallest pieces will contain the same proportion of the various particles as the largest. If oxygen be a white ball and hydrogen black, water is composed of one black and one white ball; every particle of water has a similar constitution, and no half ball can be used, and no confusion of fractions. Of course the white balls might unite to the black, and any mixture might be supposed; but it must all be definite and exact. Now this suits all the known facts in chemistry. Dalton also found that even these compound particles acted exactly like simple particles, a definite quantity always uniting with a definite quantity. The relative weight of the atom is got by the relative weight in any larger quantity analyzed. If a quantity of water weighs 9, the oxygen weighs 8, and the hydrogen 1. The atomic weight of hydrogen is called 1, oxygen 8, and the atomic weight of all bodies is according to their relation to these; 8 of oxygen unite with 28 of iron, 28 therefore is the atomic weight of iron, and so on.
In 1808 Dalton published his "New System of Chemistry," part 1st; the 2nd part in 1810; and the 2nd volume in 1827. Part 1st contained his atomic theory; but it had already been published by Professor Thomson of Glasgow, to whom he had communicated it. It had been begun at least as early as 1803. Thomson first saw its great value. Dalton's separate papers were very numerous; one hundred and sixteen titles are given of papers read to the Literary and Philosophical Society of Manchester, besides twenty-nine in journals.
He used the system of metric-analysis extensively, and published the method in 1814. He trained also several young chemists to it, who have continued it. He found, so late as 1840, that in dissolving sugar, the amount of space occupied was represented by the water only—the carbon he believed to enter between the particles of water. This he applied to solutions of hydrated salts, but much too generally. In 1816 he was made a corresponding member of the French Academy; in 1830 a foreign associate; in 1822 a fellow of the Royal Society; in 1832 a D.C.L. of Oxford, &c. In 1833 a pension of £150 was conferred on him by government; afterwards increased to £300. In 1836 his brother Jonathan died childless, and he inherited the estate, considerably increased; so that he was comparatively rich in his later years. Mr. Strutt of Derby had desired to make him independent of work, and offered him a home and laboratory, and £400 a year; but his independent mind refused the offer. In 1837 he was disabled for a time by paralysis, and was always feeble afterwards, although he made his meteorological observations to the last evening of his life. These have been reckoned at two hundred thousand in number. He died on July 27, 1844, aged nearly seventy-eight years. His life had been calm and he died calmly, a true student of nature. His funeral was a public one. A marble statue of him was made by Chantrey in 1854. It is in the hall of the Royal Institution, Manchester. A copy in bronze is placed in the most public place in that city, beside Wellington, Peel, and Watt. Two Dalton chemical scholarships, two Dalton mathematical scholarships, and ten prizes, in his honour, are attached to Owen's college.
Dalton was by no means a very ingenious experimenter; but his conceptions were clear and vigorous, and his deductions always those of a powerful and searching intellect. The great discovery by which he so prodigiously extended the boundaries of chemical science, has contributed in an unspeakable degree to the advancement both of the material and the intellectual interests of mankind. Dr. Henry, his literary executor, wrote his life, published by the Cavendish Society. There is also a memoir of him attached to a history of the atomic theory, by Dr. R. Angus Smith, published at the request of the Manchester Society.—R. A. S.
DALTON, John, an English poet and divine, was born in 1709, and died in 1763. His father, who was a rector in Cumberland, sent him to a grammar-school at Lowther, from which
