At the side of this corpuscular theory, M. Berzelius has placed another, that of volumes. As experiment proves that almost all bodies are capable of being volatilized in temperatures sufficiently elevated, it is allowable to con ceive all bodies as existing under the gaseous form, in which ;hey must of course obey the laws, discovered by M. Gay Lussac, concerning the volumes Of gases in a state of com bination. Regarding water as compounded of two mo lecules of hydrogen to one of oxygen, it follows that the weight of a volume of an elementary substance is equal to the weight of a molecule of the same substance. And hence the only difference between these two hypotheses lies in the circumstance, that the one views bodies in the solid, the other in the gaseous state. The latter is founded entirely on facts ; it is therefore less hypothetical than that of molecules, and serves better to direct our researches concerning chemical proportions. But, after all, when one attempts to form an idea of what a gas is, and of the state in which the solid particles, gasified by heat, really exist in such a substance, the speculation always reverts to molecules, and shows that both hypotheses are substan tially the same, their difference consisting solely in the words atom and volume.
What has now been laid down with regard to the state of combination among molecules, is applicable only to in organic nature. The case is widely different in the king doms of organic nature, where the great series of analo gous bodies display modes of combination much more nu merous, we might almost say, innumerable. In proof or this, we have only to consider the long list of essential oils, for example, in which the difference of specific gravity, smell, &c. prove that they cannot have the same compo sition; whilst, on the other hand, their general chemical characters prove that the difference in their composition must be very inconsiderable. How can this be reconciled with what we have just stated concerning inorganic nature ? M. Berzelius extended his experiments also to this very difficult and delicate point.; to see if it were possible to find the general differences among the laws, according to which these two different departments of nature have been form ed. He analysed the following vegetable substances : oxa lic, acetic, succinic, formic, tartaric, citric, saccolactic, benzoic, and gallic acids ; tannin, sugar, sugar of milk, gum, and starch. Although this is not the place for giv ing an account of the analytic method employed in those experiments, it may not be altogether useless to devote a few words to that point. He combined the substance to be analysed with oxyd of lead, and deprived this combina tion of all its water, and afterwards analysed it to discover the exact quantity of oxyd of lead and of vegetable mat ter contained in it. A quantity of this substance, correctly
weighed, was then burnt with superoxygenated muriate and oxymuriate of potass, in an apparatus contrived for the purpose. The water and carbonic acid extracted from it, indicated the quantity of hydrogen and carbon. The loss was the oxygen of the substance. On analyzing the fourteen substances above mentioned, he always found the oxygen of the substance to be an integer multiple of that contained by the oxyd of lead, with which it had been combined ; so that organic substances appear to obey the same law as inorganic oxyds. Now, according to the reasons already explained, the number by which the oxy gen of the analysed substance is a multiple of the oxygen contained in the oxyd of lead combined with it, must either be the number of molecules of oxygen in the analys ed substance, or else it must be an integer divisor of the number of those molecules. But, if it is allowable to con ceive substances as compounded of atoms or molecules, the resulting weights of hydrogen and of carbon must also be those of some number of entire molecules belonging to these two elements. Acetic acid, for example, is compos ed of 46.934 parts of oxygen, 46.871 parts of carbon, and G.195 parts of hydrogen. The quantity of oxyd of lead neutralized by this quantity of acetic acid, contains 15.645 parts of oxygen, and 15.645 X3 = 46.935 ; but, if this quantity of oxygen forms 3 molecules, 46.871 will form 4 molecules of carbon, and 6.195 will form 6 of hydrogen. So that each molecule of acetic acid is composed of 6 H + 4 C + 3 O. The following is a summary of the ana lytical results obtained by M. Berzelius from analysing the fourteen substances in question.
If an organic substance cannot be combined with an oxyd of composition, it is impossible to find, with any cer tainty, what number of molecules it contains ; because a very small difference in the numerical result of the analy sis, especially in the quantity of the hydrogen, may pro duce very great mistakes when the number of atoms con tained by each element is attempted to be calculated. To convince ourselves of this, we have only to compare the numbers resulting from the analysis of tartaric acid and of saccolactic acid, or the analysis of starch with that of su gar. In analysing inorganic substances, two experiments on the same substance frequently differ more widely than the analyses now mentioned.