from other substances."

There is an admirable clear-sighted

ness in his short and rapid conclusions. The same law of equal expansion of gases was published six months later by Gay Lussac, and is often called by his name. Dr. Ure says the experiments were made by Gay Lussac with much more care and exactness, but the newest results obtained by Regnault by no means speak so in favour of Gay Lussac. The difference between his results and Dalton's were only trifling. Gay Lussac gave the expansion per degree at 480, Dalton 483, Regnault 491. In this country we have generally used Gay Lussac's for no sufficient reason. On the Continent Dalton has almost been entirely deprived of his merit, and is not even mentioned in connection with it in many French and German works: but such circumstances are unfortunately of constant occurrence. It is difficult to find the reason of this, but it happens so often that our countrymen are quite omitted in their works, that it must in a great measure arise from their neglect of our literature. This certainly must be the cause, as we find that both French and Germans of high name can treat latent heat without even mentioning the name of Black, whose claims are not even disputed; this last occurs even with the very systematic Gmelin. We can readily imagine how some of the other papers of Dalton have been overlooked as merely additions to a subject, whereas he who gives the polish and establishes the law has been allowed the entire credit. They were certainly put within the reach of inquirists, as he says in a letter quoted in Dr. Henry's life of him, p. 50. My lately published essays on gases, &c., together with the more recent ones read at our society, and of which I gave the result in my late lectures, have drawn the attention of most of the philosophers of Europe. They are busy with them at London, Edinburgh, Paris, and in various parts of Germany, some maintaining one side and some another. The. truth will surely out at last." Although not alluding specially

to the last mentioned memoir, this letter alludes to his inves tigations generally, which had been everywhere discussed. On November 12th, 1802, he read to the Literary and Philosophical Society an Experimental inquiry into the proportion of the several gases or elastic fluids constituting

the atmosphere.”*

66

In describing his Eudiometric process he has a few observations of great importance, indications of the direction in which he was moving, but given in such a way as to lead us to the conclusion that he had not yet seen their value; teaching us also that an idea of definite proportions may exist without any distinct nature of the completeness of the law of equivalents as it stands. At page 249 he says,

66

"2. If 100 measures of common air be put to 36 of pure nitrous gas in a tube 3-10ths of an inch wide and 5 inches long, after a few minutes the whole will be reduced to 79 or 80 measures, and exhibit no signs of either oxygenous or nitrous gas.

"3. If 100 measures of common air be admitted to 72 of nitrous gas in a wide vessel over water, such as to form a thin stratum of air, and an immediate momentary agitation be used, there will, as before, be found 79 or 80 measures of pure azotic gas for a residuum.

"4. If in the last experiment, less than 72 measures of nitrous gas be used, there will be a residuum containing oxy

* 1st vol. of Memoirs, new series, p. 244.

genous gas; if more, then some residuary nitrous gas found.

"These facts clearly point out the theory of the pr the elements of oxygen may combine with a certain p of nitrous gas, or with twice that portion, but with no mediate quantity. In the former case nitric acid result, in the latter nitrous acid; but as both these m formed at the same time, one part of the oxygen going of nitrous gas and another to two, the quantity of nitro absorbed should be variable; from 36 to 72 per cent. for mon air. This is the principal cause of that diversity has so much appeared in the results of chemists on this sub

In the paper on the expansion of elastic fluids, h already, in a plate, shown that he was accustomed to gases as composed of definite particles, having drawn with a different form.

Immediately after this, January 28th, 1803, he read inquiry "On the tendency of elastic fluids to diffusion thr each other."* This subject was first begun by Pries The memoir which he has written on the transmissio gases through porous vessels, entitled "Experiments lating to the seeming conversion of water into air, certainly one of the most beautiful specimens of invest tion that can anywhere be found. He there establishes fact, that through porous vessels, gases pass one way, va of water and other liquids another; and observed, that mercury in one experiment had risen 3 inches above level on the outside. He afterwards found that what c take place with "air and water, will be done with any kinds of airs."

He failed, however, to make the next step, having s that it is probable "that if two kinds of air of very differ specific gravities, were put into the same vessel with v great care, they might continue separate," although

* Memoirs, Vol. 1., New Series, p. 259.

own experiments justified a different opinion. Dalton took the subject up at this stage, and says the result "establishes this remarkable fact, that a lighter elastic fluid cannot rest upon a heavier, as is the case with liquids; but they are constantly active in diffusing themselves through each other until an equal equilibrium is effected; and that without any regard to their specific gravity, except so far as it accelerates or retards the effect according to circumstances."

"The only apparatus found necessary, was a few phials and tubes with perforated corks; the tube mostly used was one 10 inches long, and of 1-20th inch bore; in some cases a tube of 30 inches in length, and 1-3rd inch bore was used; the phials held the gases that were subjects of experiment, and the tube formed the connection." p. 261. This tube was often a piece of tobacco pipe.

He believes that this proves his theory of elastic fluids to be correct, that gases are as a vacuum to each other, and it no doubt does favour it, especially as he added that they might be obstructed as a stream of water by a stony bed. Still this very explanation takes away much of the original meaning, and any of his difficulties as to the mutual action of gases must be cleared by further experiments, as has been the case with the laws of diffusion which have already been shewn to us by Professor Graham. There is no doubt that Dalton's expression is an useful attempt to grasp a great difficulty, not yet grasped, we shall see him returning to it again in the next paper.

On October 21st, 1803, he read to the Literary and Philosophical Society, another investigation "On the absorption of gases by water and other liquids." p. 271., Vol. I., New Series.

In this he says, 2. "If a quantity of water freed from air be agitated in any kind of gas not chemically uniting with water, it will absorb its bulk of the gas, or otherwise a

* Page 260, Vol. I., New Series.

part of it, equal to some one of the following fractions, namely, 1-8th, 1-27th, 1-64th, 1-125th, these being the cubes of the reciprocals of the natural numbers 1, 2, 3, &c.;" This has not found general assent, nor can it flow from any known natural law; indeed if it were true it would not shew itself by the usual mode of experimenting, as we can readily imagine one part of the water having 1-4th, another 1-5th, both being distinct parts of the whole, but so mixed with each other in the water that no result is perceived.

4. "If a quantity of water free from air be agitated with a mixture of two or more gases, such as atmospheric air, the water will absorb portions of each gas the same as if they were presented to it separately in their proper density.”

5. "If water impregnated with any one gas (as hydrogenous) be agitated with another gas equally absorbable (as azotic), there will apparently be no absorption of the latter gas; just as much gas being found after agitation as was introduced to the water; but upon examination the residuary gas will be found a mixture of the two, and the parts of each, in the water, will be exactly proportional to those out of the water."

"10. Pure distilled water, rain and spring water, contain nearly their due share of atmospheric air; if not, they quickly acquire that share by agitation in it, and lose any other gas they may be impregnated with. It is remarkable however that water by stagnation in certain circumstances loses part or all of its oxygen, notwithstanding its constant exposition to the atmosphere. This I have uniformly found to be the case in my large wooden pneumatic trough, containing about 8 gallons. * * * * The quantity of azotic gas is not materially diminished by stagnation, if at all." He has not here considered the action of the organic substances.

Theory of the absorption of gases by water. p. 283. "1. All gases that enter into water and other liquids, by means of pressure, and are wholly disengaged again by the