The constancy of these proportions left no doubt that the combinations of all gaseous bodies were definite. The theory of Dalton applied to them with great facility. We have only to consider a volume of gas to represent an atom, and then we see that in gases one atom of one gas combines either with one, two, or three atoms of another gas, and never with more. There is, indeed, a difficulty occasioned by the way in which we view the composition of water. If water be composed of one atom of oxygen and one atom of hydrogen, then it follows that a volume of oxygen contains twice as many atoms as a volume of hydrogen. Consequently, if a volume of hydrogen gas represent an atom, half a volume of oxygen gas must represent an atom.
Dr. Prout soon after showed that there is an intimate connexion between the atomic weight of a gas and its specific gravity. This indeed is obvious at once.I afterwards showed that the specific gravity of a gas is either equal to its atomic weight multiplied by 1·111[.1] (the specific gravity of oxygen gas), or by 0·555[.5] (half the specific gravity of oxygen gas), or by O·277[.7] (1-4th of the specific gravity of oxygen gas),(1-4th of the specific gravity of oxygen gas), these differences depending upon the relative condensation which the gases undergo when their elements unite. The following table exhibits the atoms and specific gravity of these three sets of gases:
| I. Sp. Gr. = Atomic Weight × 1·111[.1] | ||
|---|---|---|
| Atomic weight. | Sp. gravity. | |
| Oxygen gas | 1 | 1·1111 |
| Fluosilicic acid | 3·25 | 3·6111 |
| II. Sp. Gr. = Atomic Weight × 0·555[.5]. | ||
|---|---|---|
| Atomic weight. | Sp. gravity. | |
| Hydrogen | 0·125 | 0·069[.4] |
| Azotic | 1·75 | 0·072[.2] |
| Chlorine | 4·5 | 2·5 |
| Carbon vapour | 0·75 | 0·416[.6] |
| Phosphorus vapour | 2 | 1·111[.1] |
| Sulphur vapour | 2 | 1·111[.1] |
| Tellurium vapour | 4 | 2·222[.2] |
| Arsenic vapour | 4·75 | 2·638[.8] |
| Selenium vapour | 5 | 2·777[.7] |
| Bromine vapour | 10 | 5·555[.5] |
| Iodine vapour | 15·75 | 8·75 |
| Steam | 1·125 | 0·625 |
| Carbonic oxide gas | 1·75 | 0·972[.2] |
| Carbonic acid | 2·75 | 1·527[.7] |
| Protoxide of azote | 2·75 | 1·527[.7] |
| Nitric acid vapour | 6·75 | 3·75 |
| Sulphurous acid | 4 | 2.222[.2] |
| Sulphuric acid vapour | 5 | 2·777[.7] |
| Cyanogen | 3·25 | 1·805[.5] |
| Fluoboric acid | 4·25 | 2·361[.1] |
| Bisulphuret of carbon | 4·75 | 2·638[.8] |
| Chloro-carbonic acid | 6·25 | 3·472[.2] |
| III. Sp. Gr. = Atomic Weight × 0·277[.7]. | ||
|---|---|---|
| Atomic weight. | Sp. gravity. | |
| Ammoniacal gas | 2·125 | 0·5902[.7] |
| Hydrocyanic acid | 3·375 | 0·9375 |
| Deutoxide of azote | 3·75 | 1·041[.6] |
| Muriatic acid | 4·625 | 1·2847[.2] |
| Hydrobromic acid | 10·125 | 2·8125 |
| Hydriodic acid | 15·875 | 4·40973 |
When Professor Berzelius, of Stockholm, thought of writing his Elementary Treatise on Chemistry, the first volume of which was published in the year 1808, he prepared himself for the task by reading several chemical works which do not commonly fall under the eye of those who compose elementary treatises. Among other books he read the Stochiometry of Richter, and was much struck with the explanations there given of the composition of salts, and the precipitation of metals by each other. It followed from the researches of Richter, that if we were in possession of good analyses of certain salts, we might by means of them calculate with accuracy the composition of all the rest. Berzelius formed immediately the project of analyzing a series of salts with the most minute attention to accuracy. While employed in putting this project in execution, Davy discovered the constituents of the alkalies and earths, Mr. Dalton gave to the world his notions respecting the atomic theory, and Gay-Lussac made known his theory of volumes. This greatly enlarged his views as he proceeded, and induced him to embrace a much wider field than he had originally contemplated. His first analyses were unsatisfactory; but by repeating them and varying the methods, he detected errors, improved his processes, and finally obtained results, which agreed exceedingly well with the theoretical calculations. These laborious investigations occupied him several years. The first outline of his experiments appeared in the 77th volume of the Annales de Chimie, in 1811, in a letter addressed by Berzelius to Berthollet. In this letter he gives an account of his methods of analyses together with the composition of forty-seven compound bodies. He shows that when a metallic protosulphuret is converted into a sulphate, the sulphate is neutral; that an atom of sulphur is twice as heavy as an atom of oxygen; and that when sulphite of barytes is converted into sulphate, the sulphate is neutral, there being no excess either of acid or base. From these and many other important facts he finally draws this conclusion: "In a compound formed by the union of two oxides, the one which (when decomposed by the galvanic battery) attaches itself to the positive pole (the acid for example) contains two, three, four, five, &c., times as much oxygen, as the one which attaches itself to the negative pole (the alkali, earth, or metallic oxide)." Berzelius's essay itself appeared in the third volume of the Afhandlingar, in 1810. It was almost immediately translated into German, and published by Gilbert in his Annalen der Physik. But no English translation has ever appeared, the editors of our periodical works being in general unacquainted with the German and other northern languages. In 1815 Berzelius applied the atomic theory to the mineral kingdom, and showed with infinite ingenuity that minerals are chemical compounds in definite or atomic proportions, and by far the greater number of them combinations of acids and bases. He applied the theory also to the vegetable kingdom by analyzing several of the vegetable acids, and showing their atomic constitution. But here a difficulty occurs, which in the present state of our knowledge, we are unable to surmount. There are two acids, the acetic and succinic, that are composed of exactly the same number, and same kind of atoms, and whose atomic weight is 6·25. The constituents of these two acids are
| Atomic weight. | |
| 2 atoms hydrogen | 0·25 |
| 4 " carbon | 3 |
| 3 " oxygen | 3 |
| 6·25 |
So that they consist of nine atoms. Now as these two acids are composed of the same number and the same kind of atoms, one would expect that their properties should be the same; but this is not the case: acetic acid has a strong and aromatic smell, succinic acid has no smell whatever. Acetic acid is so soluble in water that it is difficult to obtain it in crystals, and it cannot be procured in a separate state free from water; for the crystals of acetic acid are composed of one atom of acid and one atom of water united together; but succinic acid is not only easily obtained free from water, but it is not even very soluble in that liquid. The nature of the salts formed by these two acids is quite different; the action of heat upon each is quite different; the specific gravity of each differs. In short all their properties exhibit a striking contrast. Now how are we to account for this? Undoubtedly by the different ways in which the atoms are arranged in each. If the electro-chemical theory of combination be correct, we can only view atoms as combining two by two. A substance then, containing nine atoms, such as acetic acid, must be of a very complex nature. And it is obvious enough that these nine atoms might arrange themselves in a great variety of binary compounds, and the way in which these binary compounds unite may, and doubtless does, produce a considerable effect upon the nature of the compound formed. Thus, if we make use of Mr. Dalton's symbols to represent the atoms of hydrogen, carbon and oxygen, we may suppose the nine atoms constituting acetic and succinic acid to be arranged thus:
Or thus: