Substances, whether in the solid, liquid, or gaseous state, possess properties which are independent of the force of cohesion; but they also posses others which appear to be modified by this force (so variable in its intensity), and which no longer follow any regular law. The same pressure applied to all solid or liquid substances would produce a diminution of volume differing in each case, while it would be equal for all elastic fluids. Similarly, heat expands all substances; but the dilations of liquids and solids have hitherto presented no regularity, and it is only those of elastic fluids which are equal and independent of the nature of each gas. The attraction of the molecules in solids and liquids is, therefore, the cause which modifies their special properties; and it appears that it is only when the attraction is entirely destroyed, as in gases, that bodies under similar conditions obey simple and regular laws. At least, it is my intention to make known some new properties in gases, the effects of which are regular, by showing that these substances combine amongst themselves in very simple proportions, and that the contraction of volume which they experience on combination also follows a regular law. I hope by this means to give a proof of an idea advanced by several very distinguished chemists--that we are perhaps not far removed from the time when we shall be able to submit the bulk of chemical phenomena to calculation.
It is a very important question in itself, and one much discussed amongst chemists, to ascertain if compounds are formed in all sorts of proportions. M. Proust, who appears first to have fixed his attention on this subject, is of opinion that the metals are susceptible of only two degrees of oxidation, a minimum and a maximum; but led away by this seductive theory, he has seen himself forced to entertain principles contrary to physics in order to reduce to two oxides all those which the same metal sometimes presents. M. Berthollet thinks, on the other hand--reasoning from general considerations and his own experiments--that compounds are always formed in very variable proportions, unless they are determined by special causes, such as crystallisation, insolubility, or elasticity. Lastly, Dalton has advanced the idea that compounds of two bodies are formed in such a way that one atom of the one unites with one, two, three, or more atoms of the other. It would follow from this mode of looking at compounds that they are formed in constant proportions, the existence of intermediate bodies being excluded, and in this respect Dalton's theory would resemble that of M. Proust; but M. Berthollet has already strongly opposed it in the Introduction he has written to Thomson's Chemistry, and we shall see that in reality it is not entirely exact. Such is the state of the question now under discussion; it is still very far from receiving its solution, but I hope that the facts which I now proceed to set forth, facts which have entirely escaped the notice of chemists, will contribute to its elucidation.
Suspecting, from the exact ratio of 100 of oxygen to 200 of hydrogen, which M. Humboldt and I had determined for the proportions of water, that other gases might also combine in simple ratios, I have made the following experiments. I prepared fluoboric, muriatic, and carbonic gases, and made them combine successively with ammonia gas. 100 parts of muriatic gas saturate precisely 100 parts of ammonia gas, and the salt which is formed from them is perfectly neutral, whether one or the other of the gases is in excess. Fluoboric gas, on the contrary, unites in two proportions with ammonia gas. When the acid gas is put first into the graduated tube, and the other gas is then passed in, it is found that equal volumes of the two condense, and that the salt formed is neutral. But if we begin by first putting the ammonia gas into the tube, and then admitting the fluoboric gas in single bubbles, the first gas will then be in excess with regard to the second, and there will result a salt with excess of base, composed of 100 of fluoboric gas and 200 ammonia gas. It may, however, be proved that neutral carbonate of ammonia would be composed of equal volumes of each of these components. M. Berthollet, who has analysed this salt, obtained by passing carbonic gas into the sub-carbonate, found that it was composed of 73.34 parts by weight of carbonic gas and 26.66 of ammonia gas. Now, if we suppose it to be composed of equal volumes of its components, we find from their known specific gravity, that it contains by weight
| 71.81 | of carbonic acid |
| 28.19 | of ammonia |
| 100.00 |
If the neutral carbonate of ammonia could be formed by the mixture of carbonic gas and ammonia gas, as much of one gas as of the other would be absorbed; and since we can only obtain it through the intervention of water, we must conclude that it is the affinity of this liquid which competes with that of the ammonia to overcome the elasticity of the carbonic acid, and that the neutral carbonate of ammonia can only exist through the medium of water.
Thus we may conclude that muriatic, fluoboric, and carbonic acids take exactly their own volume of ammonia gas to form neutral salts, and that the last two take twice as much to form sub-salts. It is very remarkable to see acids so different from one another neutralise a volume of ammonia gas equal to their own; and from this we may suspect that if all acids and all alkalis could be obtained in the gaseous state, neutrality would result from the combination of equal volumes of acid and alkali.
It is not less remarkable that, whether we obtain a neutral salt or a sub-salt, their elements combine in simple ratios which may be considered as limits to their proportions. Accordingly, if we accept the specific gravity of muriatic acid determined by M. Biot and myself, and those of carbonic gas and ammonia given by M. Biot and Arago, we find that dry muriate of ammonia is composed of
| Ammonia, | 100.0 | or | 38.35 |
| Muriatic acid, | 160.7 | 61.65 | |
| 100.00 |
| 100 | of ammonia |
| 213 | of acid. |
| Ammonia, | 100.0 | or | 43.98 |
| Carbonic acid, | 127.3 | 56.02 | |
| 100.00 |
| Ammonia, | 100.0 | or | 28.19 |
| Carbonic acid, | 254.6 | 71.81 | |
| 100.00 |
We might even now conclude that gases combine with each other in very simple ratios; but I shall still give some fresh proofs.
According to the experiments of M. Amédée Berthollet, ammonia is composed of
| 100 of nitrogen |
| 300 of hydrogen, |
I have found ... that sulphuric acid is composed of
| 100 of sulphurous gas, |
| 50 of oxygen gas. |
| 100 of carbonic oxide gas, |
| 50 of oxygen gas. |
| Nitrogen | Oxygen | |
|---|---|---|
| Nitrous oxide | 63.30 | 36.70 |
| Nitrous gas | 44.05 | 55.95 |
| Nitric acid | 29.50 | 70.50 |
| Nitrogen | Oxygen | |
|---|---|---|
| Nitrous oxide | 100 | 49.5 |
| Nitrous gas | 100 | 108.9 |
| Nitric acid | 100 | 204.7 |
We may then admit the following numbers for the proportions by volume of the compounds of nitrogen with oxygen:
| Nitrogen | Oxygen | |
|---|---|---|
| Nitrous oxide | 100 | 50 |
| Nitrous gas | 100 | 100 |
| Nitric acid | 100 | 200 |
Auf diesem Webangebot gilt die Datenschutzerklärung der TU Braunschweig mit Ausnahme der Abschnitte VI, VII und VIII.