This compound is white; and, when dried, it becomes greenish; but I have never obtained it of the same degree of saturation when prépared by different processes. The tannin in it was always combined with more than 11 times as much base as in the neutral tánnate; though it never contained so much as twice that quantity. I analyzed tannin by employing for the combustion both supertannate and tannate as neutral as possible, and the analyses furnished the same result : 0:4 of tannin produced 0.1425 water and 0.7625 carbonic acid. Hence tannin of nutgalls is composed of Hydrogen 4.186 Carbon 51:160 Oxygen 44.654 which salts atten will how differ who Filli fctly 100.000 PE STOLE carbo But we have seen that 100 of tannin combine with 52 oxide of lead, the oxygen in which is 3.718. Now 3-718 x 12 = 44.616. Hence we may conclude that tannin contains 12 volumes of oxygen. But there is no doubt that there must be an analogy between gallic acid and tannin, and this analogy can scarcely be any thing else . than the same compound radicle combined with different volumes of oxygen. Supposing, then, that tannin, like gallic acid, contains equal volumes of carbon and hydrogen, and that it is 12 0 + 18 C + 18 H, or (which comes to the same thing) 40 + 6C + 6 H, its composition ought to be per cent. Hydrogen 4:45 Carbon .. 50:55 Oxygen .. 45.00 N 100.00 Here we find a little more hydrogen and a little less carbon than the analysis indicates. This is a necessary consequence of the dishydrogenation which tannia undergoes by exposure to the air, in consequence of which the colour of its combinations becomes darker and darker; so that we never can procure this substance in a perfect state, excepting in fresh nutgalls in which the tannin is not yet coloured. (To be continued.) ARTICLE IV. Observations on some Points connected with the Atomic Theory. By Thomas Thomson, M.D. F.R.S. PROFESSOR BERZELIUS, having in his important dissertations on this subject published in the second, third, fourth, and fifth + 5+ volumes of the Annals of Philosophy, pointed out some difficulties which present themselves when we apply the atomic theory to the salts, and having in a recent paper refused to admit Mr. Dalton's attempts to remove these difficulties as validmperhaps the reader will not be displeased if I state here, in as few words as possible, how I have been in the habit of viewing these difficulties when they happened to present themselves during my examination of the different genera of salts. When a difficulty occurs in any branch of chemical investigation, the greater number of persons there are who attempt to explain it, so much the sooner, in all probability, will it be removed. Even should my explanations not prove perfectly satisfactory, they may serve to convey a lucky thought to some other person, who may be more fortunate in his endeavours. 1. It appears from the tables of the sulphates, carbonates, and nitrates, published in the second and third volumes of the Annals of Philosophy, that the yellow oxide of lead combines always with two integrant particles of acid when it constitutes neutral sulphate, carbonate, and nitrate of lead. The same law holds in the phosphate, borate, oxalate, and all the other neutral salts of lead, Nitrate of lead is composed of ...... 2 n t il : 41.580 Sulphate of potash +1p 11.000 52-580 Now if we mix 41.58 grains of nitrate of lead with 11 grains of sulphate of potash a double decomposition will take place, and two neutral salts will be produced, namely, nitrate of potash and sulphate of lead, composed as follows :Nitrate of potash .... In + 1 p 12.803 Sulphate of lead 2 st ) ? 37.974 50-777 Now it is obvious to the eye that if the two salts be composed as we have supposed, such a double decomposition is impossible, The first two salts contain two integrant particles of nitric acid ; the last two, only one integrant particle; while, on the contrary, there is only one integrant particle of sulphuric acid in the first two salts, but two in the last two. The weight of the first two salts is 52:58 grains; that of the last two, 50•777 grains. Thus about two grains of weight are lost by the decomposition; while a particle of nitric acid must be transmuted into a particle of sulphuric acid. The same absurdities and contradictions will be found to take place whenever we attempt to reduce any double decomposition, by means of a salt of lead, to calculation. It is very obvious, from the appearance of these contradictions and absurdities, that there must exist some error in our tables that the salts of lead cannot be constituted as we have supposed them. Now a very slight alteration will remove all the anomalies, and render the composition of the salts of lead quite conformable to experiment. Reduce the weight of an integrant particle of yellow oxide of lead to one-half the weight which I have given it in my original table, published in the second volume of the Annals of Philosophy. Let the weight be 13.987 instead of 27.974. In that case all the salts of lead will be composed of one integrant particle of acid and one integrant particle of oxide of lead; we have Nitrate of lead composed of In to Il 20.790 Sulphate of potash Is + 1 p 11.000 31.790 12.803 18.987 31.790 Here the double decomposition is obviously possible. The weight of the first two salts is just the same as that of the last two, and the number of integrant particles is the same in both. It seems to me to be absolutely necessary to remove this anomaly from the salts of lead ; nor do I see any other method of doing so except the one I have just now proposed ; but if we reduce the weight of an integrant particle of yellow oxide of lead to one-half, it is obvious that it must no longer be considered as a compound of 1 atom lead + 2 atoms oxygen, but of 1 atom lead + ) atom oxygen. It will be a protoxide instead of a deutoxide. If so, provided it be true that the brown oxide contains just twice as much oxygen as the yellow oxide, numbers adopted on the authority of Berzelius, the brown oxide must be a deutoxide of lead composed of 1 atom lead + 2 atoms oxygen. The red oxide, which is intermediate, must be considered as a compound of one integrant particle of yellow oxide and one integrant particle of brown oxide. This notion was first suggested by Proust, and appears to have been adopted by Mr. Dalton. I own that in consequence of the anomaly which I have just pointed out I have been for some time inclined to the same opinion; but a desire previously to examine the properties of the red oxide of lead under this point of view has hitherto prevented me from making any alteration in the weight of an atom of lead. Berzelius refuses to adopt this opinion. There is, no doubt, another method of getting rid of the anomaly which has been pointed out above without having recourse to it; namely, to double the weight of an atom of all the other metals; but that method would be attended with much greater inconveniences, and could not therefore be adopted with propriety. I do not see any alterpative, therefore, in the present state of our knowledge, but that of adopting the opinion of Proust respecting the nature of red lead, and considering yellow oxide of lead as a protoxide. If any person has taken the trouble to study the tables of the saļts which I have published, he will have been struck with some other anomalies of a similar nature to those belonging to the salts of lead; but I forbear touching upon them at present, till we are in possession of more perfect analyses than have been hitherto published. 2. Certain salts have been analyzed, the composition of which, when stated in symbols, presents us with the anomaly of li atoms of one substance combined with one atom of another. Thus subsulphate of iron is composed thus, 1 (8 03) + ! (F 02); or it contains one integrant particle of sulphuric acid and i} integrant particle of black oxide of iron. As such a composition is obviously impossible, it is clear that in such cases a certain number of integrant particles of sulphuric acid must be combined with a certain. number of integrant particles of oxide of iron. If we multiply by two, the anomaly will disappear. We shall then have 2 (S 09) + 3 (F 0%); that is to say, the salt is a compound of two integrant particles of sulphuric acid and three integrant particles of black oxide of iron. Such combinations do not present any thing incompatible with the atomic theory, which admits of such combinations ; but they constitute exceptions to one of the general laws which Berzelius has deduced from his numerous analyses. The law is, that in all inorganic compounds one of the constituents always enters in the state of a single atom. In the subsulphate of iron there is no single atom, either simple or compound. "It consists of 12 atoms of oxygen, three of iron, and two of sulphur; or of two integrant particles of sulphuric acid and three integrant particles of black oxide of iron. The composition of the subsulphate of copper may be explained in the same way. Its symbol is 1 (SOS) + 09 14 (CO2), or one integrant particle of sulphuric acid combined with 1 integrant particle of black oxide of copper. If we multiply by two we obtain 2 (S 09) + 3 (COR), which I conceive to be the real constitution of the salt; namely, a compound of two integrant particles of sulphuric acid with three integrant particles of black oxide of copper. The subarseniate of lead admits of the same explanation. Its symbol is 1 (As OS) + 11 (P 0%), or one integrant particle of arsenic acid combined with 14 integrant particle of yellow oxide of lead. When we multiply by two we obtain 2 (As 0%) + 3 (P 02); that is, two integrant particles of arsenic acid united with three integrant particles of yellow oxide of lead. Various other similar examples might be adduced ; but they are all explicable in the same way. They appear to me to constitute so many exceptions to Berzelius's law above-mentioned, and to show that it does not hold so universally as he had supposed. 3. Professor Berzelius has just favoured the chemical world with an analysis of a considerable number of the vegetable acids, and some other vegetable substances. That these experiments have been conducted with the greatest care is evident from the details into which Berzelius has entered ; nor have I the least doubt, from the uncommon precision which characterizes whatever is done by this of the very skilful chemist, that his results furnish very near approximations to the truth ; but from the extreme difficulty attending such analyses, I do not conceive that perfect precision can be attained at first; but think that the atomic theory furnishes us with such additional checks that, by a judicious application of them to the constitution of these acids as determined by Berzelius, we may obtain results approaching exceedingly near the truth. I shall at present apply that theory to the investigation of the composition of oxalic acid. According to Berzelius, that acid is composed as follows:-Oxygen 66.534 6 atoms Carbon 33:222 4 Hydrogen 0.244 But as I consider the weight of an atom of hydrogen as twice as great as Berzelius makes it, we must, in order to represent the composition of this acid according to my numbers, 'double the number of atoms of oxygen and carbon which it contains. It will then be composed of Oxygen 12 atoms Carbon 8 Hydrogen 1 21 So that it is a very complicated body. The weight of an integrant particle of it mụst be 18.140. We might, indeed, reduce the number of atoms in this acid to 11 by doubling the quantity of hydrogen, obtained by Berzelius; for the difference seems to be within the limits of the unavoidable errors to which sạch experiments are liable. But Berzelius does not think that he could have committed any such error. Let us, therefore, have recourse to another method of determining the weight of an integrant particle of oxalic acid. From the analysis of oxalate of lead made with great care by Berzelius it appears to be a compound of Oxalic acid 100 Yellow oxide of lead 307.5 Now there can be no doubt, from a comparison of all the genera of salts hitherto examined, that oxalate of lead is a compound of two integrant particles of oxalic acid and one integrant particle of Yellow oxide of lead; so that to find the weight of an integrant particle of oxalic acid we have this proportion :-307.5 : 27.974 : 4:548 = an integrant particle of oxalic acid. Now this is just the fourth part of the weight of that acid resulting from the 100 2 |