From my experiments, which differ very little from those of M. Chenevix, oxygenated muriatic acid is composed by weight of 22.92 Converting these quantities into volumes, we find that oxygenated Oxygen.. Muriatic acid... Thus it appears evident to me that gases always combine in the simplest proportions when they act on one another; and we have seen in reality in all the preceding examples that the ratio of combination is I to I, I to 2, or 1 to 3. It is very important to observe that in considering weights there is no simple and finite relation between the elements of any one compound; it is only when there is a second compound between the same elements that the new proportion of the element that has been added is a multiple of the first quantity. Gases, on the contrary, in whatever proportions they may combine, always give rise to compounds whose elements by volume are multiples of each other. Not only, however, do gases combine in very simple proportions, as we have just seen, but the apparent contraction of volume which they experience on combination has also a simple relation to the volume of the gases, or at least to that of one of them. I have said, following M. Berthollet, that 100 parts of carbonic oxide gas, prepared by distilling oxide of zinc and strongly calcined charcoal, produce 100 parts of carbonic gas on combining with 50 of oxygen. It follows from this that the apparent contraction of the two gases is precisely equal to the volume of oxygen gas added. The density of carbonic gas is thus equal to that of carbonic oxide gas plus half the density of oxygen gas; or, conversely, the density of carbonic oxide gas is equal to that of carbonic gas, minus half that of oxygen. gas. Accordingly, taking the density of air as unity, we find the density of carbonic oxide gas to be 0.9678, instead of 0.9569 experimentally determined by Cruickshanks. We know, besides, that a given volume of oxygen produces an equal volume of carbonic acid; consequently oxygen gas doubles its volume on forming carbonic oxide gas with carbon, and so does carbonic gas on being passed over red-hot charcoal. Since oxygen produces an equal volume of carbonic gas, and the density of the latter is well known, it is easy to calculate the proportion of its elements. In this way we find that carbonic gas is composed of 27.38 of carbon, and carbonic oxide of 42.99 of carbon, 57.01 of oxygen. Pursuing a similar course, we find that if sulphur takes 100 parts of oxygen to produce sulphurous acid, it takes 150 parts to produce sulphuric acid. As a matter of fact, we find that sulphuric acid, according to the experiments of MM. Klaproth, Bucholz, and Richter, is composed of 100 parts by weight of sulphur and 138 of oxygen. On the other hand sulphuric acid is composed of 2 parts by volume of sulphurous gas, and I of oxygen gas. Consequently the weight of a certain quantity of sulphuric acid should be the same as that of 2 parts of sulphurous acid and I of oxygen gas, i. e., 2x2.265, plus 1.10359= 5.63359; seeing that, according to Kirwan, sulphurous gas weighs 2.265, the density of air being taken as unity. But from the proportion of 100 of sulphur to 138 of oxygen, this quantity contains 3.26653 of oxygen, and if we subtract from it 1.10359 there will remain 2.16294 for the weight of oxygen in 2 parts of sulphurous acid, or 1.08147 for the weight of oxygen contained in I part. Now as this last quantity only differs by 2 per cent. from 1.10359, which represents the weight of I part of oxygen gas, it must be concluded that oxygen gas, in combining with sulphur to form sulphurous gas, only experiences a diminution of a fiftieth of its volume, and this would probably be nil if the data I have employed were more exact. On this last supposition, using Kirwan's value for the specific gravity of sulphurous gas, we should find that this acid is composed of 100.00 of sulphur, But if, adopting the preceding proportions for sulphuric acid, we allow, as appears probable, that 100 of sulphurous gas contain 100 of oxygen gas, and that 50 have still to be added to convert it into sulphuric acid, we shall obtain for the proportions in sulphurous acid 100.00 of sulphur, 92.0 of oxygen. Its specific gravity calculated on the same suppositions, and referred to that of air, would be 2.30314, instead of 2.2650 as Kirwan found directly. Phosphorus is very closely connected with sulphur, seeing that both have nearly the same specific gravity. Consequently phosphorus should take up twice as much oxygen to become phosphorous acid, as to pass from this state into phosphoric acid. Since the latter is composed, according to Rose, of 100.0 of phosphorus, it follows that phosphorous acid should contain 100.0 of phosphorus, 76.0 of oxygen. We have seen that 100 parts of nitrogen gas take 50 parts of oxygen gas to form nitrous oxide, and 100 of oxygen gas to form nitrous gas. In the first case, the contraction is a little greater than the volume of oxygen added; for the specific gravity of nitrous oxide, calculated on this hypothesis, is 1.52092, while that given by Davy is 1.61414. But it is easy to show, from some of Davy's experiments, that the apparent contraction is precisely equal to the volume of oxygen gas added. On passing the electric spark through a mixture of 100 parts of hydrogen and 97.5 of nitrous oxide the hydrogen is destroyed, and 102 parts of nitrogen remain, including that quantity which is almost always mixed with the hydrogen, and a little of the latter gas which has escaped combustion. The residue, after making all corrections, would be very nearly equal in volume to the nitrous oxide employed. Similarly, on passing the electric spark through a mixture of 100 parts of phosphuretted hydrogen and 250 of nitrous oxide, water and phosphoric acid are formed, and exactly 250 parts of nitrogen remain,-another evident proof that the apparent contraction of the elements of nitrous oxide is equal to the whole volume of oxygen added. From this circumstance, its specific gravity referred to that of air should be 1.52092. The apparent contraction of the elements of nitrous gas appears, on the other hand, to be nil. If we admit, as I have shown, that it is composed of equal parts of oxygen and nitrogen, we find that its density, calculated on the assumption that there is no contraction, is 1.036, while that determined directly is 1.038. Saussure found that the density of water vapour is to that of air as 10 is to 14. Assuming that the contraction of volume of the two gases is only equal to the whole volume of oxygen added, we find instead of this a ratio of 10 to 16. This difference, and the authority of a physicist so distinguished as Saussure, would seem to be enough to make us reject the assumption I have just made; but I shall mention several circumstances that render it very probable. Firstly, it has a very strong analogy in its favour; secondly, M. Tralès found by direct experiment that the ratio of the density of water-vapour to air is 10 to 14.5, instead of 10 to 14; thirdly, although we do not know very exactly the volume occupied by water on passing into the elastic state, we do know, from the experiments of Watt, that a cubic inch of water produces nearly a cubic foot of steam, i. e., a volume 1728 times as great. Now, adopting Saussure's ratio, we find only 1488 for the volume occupied by water when it is converted into steam; but adopting the ratio of 10 to 16, we should have 1700.6. Finally, the refraction of water-vapour, calculated on the assumption of the ratio 10 to 14, is a little greater than the observed refraction; but that calculated from the ratio 10 to 16 is much more in harmony with the results of experiment. These, then, are the considerations which go to make the ratio 10 to 16 very probable. Ammonia gas is composed of three parts by volume of hydrogen and one of nitrogen, and its density compared to air is 0.596. But if we suppose the apparent contraction to be half of the whole volume, we find 0.594 for the density. Thus it is proved, by this almost perfect concordance, that the apparent contraction of its elements is precisely half the total volume, or rather double the volume of nitrogen. I have already proved that oxygenated muriatic gas is composed of 300 parts of muriatic gas and 100 of oxygen gas. Admitting that the apparent contraction of the two gases is half the whole volume, we find 2.468 for its density, and by experiment 2.470. I have also assured myself by several experiments that the proportions of its elements are such that it forms neutral salts with the metals. For example, if we pass oxygenated muriatic gas over copper, there is formed a slightly acid green muriate, and a little oxide of copper is precipitated, because the salt cannot be obtained perfectly neutral. It follows from this that in all the muriates, as in oxygenated muriatic acid, the acid reduced to volume is thrice the oxygen. It would be the same for carbonates and fluorides, the acids of which have for equal volumes the same saturation capacity as muriatic acid. We see, then, from these various examples, that the contraction experienced by two gases on combination is in almost exact relation with their volume, or rather with the volume of one of them. Only very slight differences exist between the densities of compounds obtained by calculation and those given by experiment, and it is probable that, on undertaking new researches, we shall see them vanish entirely. AVOGADRO AMADEO AVOGADRO was born in Turin, Italy, August 9, 1776. He studied law at the Turin University and received his doctor's degree in 1796. For the next ten years he was in the government employ. He did not begin his scientific work until 1806. In 1809 he was made professor of physics at Vercelli. After considering the recently discovered laws that all gases expand alike for like temperature and pressure, that they combine in definite multiple proportions by volume and weight to make a definite volume of the compound, he advanced the theory that this could occur only if the molecules of all gases are the same distance apart for the same temperature and pressure, that is, that the same volume, under like conditions, always contains the same number of molecules. It was long before this law was accepted, but half a century later its truth became pretty well acknowledged. The law, of course, implies that the weights of the same volume of two gases are in the same relation as their molecular weights. In 1820 he became professor of physics at Turin University. He died July 9, 1865. A still further extension of the atomic theory was made by Pierre Louis Dulong. Dulong was born at Rouen, France, February 12, 1785. He was one of Berthollet's pupils. In 1813 with Petit he discovered that elementary atoms have the same capacity for heat in proportion to their atomic weights. Dulong died in 1838. Thus by the labors of Dalton, Gay-Lussac, Avogadro, and Dulong, the greatest theory of chemistry and one of the greatest of all the natural sciences was developed and established. THE MOLECULES IN GASES PROPORTIONAL TO THE VOLUMES I. M. Gay-Lussac has shown in an interesting Memoir (Mémoires de la Société d'Arcueil, Tome II.) that gases always unite in a very simple |
