sugar of milk 40 + 5 C + 10 H, or, according to the composition of saccolate of ammonia, 8 0 + 10 C + 16 H, which constitute per cent. Hydrogen ... Sugar of milk then contains more carbon and less oxygen than common sugar. This explains why, when we burn the compound of these two bodies with oxide of lead, the first reduces much more lead than the other. We understand also why sugar of milk is more easily carbonized than common sugar. 12. Gum Arabic.-I mixed caustic ammonia with a filtered and boiling solution of gum arabic. I then mixed it with a solution of subnitrate of lead, likewise boiling hot. I took care not to add enough to precipitate the whole of the gum. I decanted off the liquid from the precipitate, which I washed repeatedly with boiling water. I then subjected it to pressure, and dried it in a vacuum, finally exposing it to the heat of 2120. When analyzed by combustion, the gummate of lead left for residue 38 25 per cent. of oxide of lead. It was therefore composed of The oxygen of these 62.105 of oxide of lead is 4:44. To obtain a subgummate of lead I digested a solution of gum with oxide of lead. A subgummate was formed, very heavy and coherent; but which could not be entirely separated from the gummy liquid. Of course I was unable to analyze it. 0'648 of gummate of lead, equivalent to 0.4 of gum, produced by combustion 0.2297 of water, and 0.617 of carbonic acid, equivalent to 6.75 per cent. of hydrogen, and 41.956 of carbon. 0.4 of gum arabic, in the state of a fine powder and dried in a vacuum at the temperature of 212°, produced by combustion 0.231 water and 0.6196 of carbonic acid, equivalent to 6.788 per cent. of hydrogen and 41.906 of carbon. Hence it apppears, that dried gum arabic contains no water; for it is probable that gummate, of lead cannot retain water with greater force than the other combina. tions having oxide of lead for their base. Gum arabic is then composed as follows: But we see that gum arabic ought to contain 12 times as much water as the base by which it is saturated: for 4:44 × 12 = 53.28. This small difference ought to be ascribed to a small error in the analysis, or in the preparation of gummate of lead; which error is in the present case increased 12 fold in the calculation. But if gum arabic contain 12 atoms of oxygen it must contain 13 of carbon and 24 of hydrogen, which make in 100 parts This agrees very well with the result of direct experiments. Gum arabic then is 12O+ 13 C + 24 H. The analysis of Gay-Lussac and Thenard gave 6.93 hydrogen, 42.23 carbon, and 50.84 oxygen. I ought to observe, that in my experiments, gum, whether pure or combined with oxide of lead, produced traces of nitric acid; so that what in the analysis I considered as pure hydrogen, contains in fact a trace of the radicle of nitric acid; which, as is known, has the same capacity for oxygen that hydrogen has. I am, however, far from pretending that gum arabic contains nitricum among its elements. It is more probable, that the formation of the nitric acid is owing to the presence of a small quantity of vegetable albumen in the gum. Probably the excess of of a per cent. of carbon obtained in the analysis, is owing to the same cause. Gum arabic, when incinerated, leaves a small quantity of ashes, the weight of which is very variable; and, of course, it cannot be considered as an essential constituent of the gumn. So much the less, as both Vauquelin and Cruikshanks found that gum contained vegetable salts with a base of lime. To see whether gum contained any secondary element, I endeavoured to separate it from gummate of lead. I found that this could not be accomplished either by means of sulphuric acid, or sulphureted hydrogen; for the disengaged gum causes the insoluble precipitates to pass through the filter, and it prevents them from being ever deposited. I therefore dissolved gummate of lead in acetic acid, and into the solution I poured alcohol, which precipitated the gum. I washed the gum very well in alcohol. This gum, being dried and burnt in a glass capsule, left oxide of lead, retained probably in the state of a super-gummate of lead. The ashes were easily soluble in acetic acid. The liquid being evaporated to dryness, and burnt, left sulphate of lime, with traces of sulphate of potash, weighing together of a per cent. of the gum. But sulphuric acid constituting more than one half of these ashes, it appears that the small quantity of the radicles of the bases cannot be considered as of any value in the composition of gum arabic, Thenard and Gay-Lussac obtained 24 per cent. of the gum in ashes, of which they kept an account in the exposition of the result of their analysis of gum arabic. These ashes consisted chiefly of carbonate of lime, the carbonic acid of which constituted nearly one per cent of the gum. No attention was paid to this; so that what they considered as 100 gum, was in reality 101. Such an error is too considerable to be neglected. Gum in its ordinary state contains water; but this water is a hygroscopic substance, whose quantity varies according to the state of the hygrometer. I have found that gum in powder, dried in a vacuum at the temperature of 212, lost about 17 per cent. of water. From this we may conclude, that gum ought to contain a quantity of water, the oxygen in which is that in the gum. I have not found that gum when dried slowly forms other combinations with water. 13. Potatoe Starch.-I took some potatoe starch, mixed it with a little water, and poured it by small portions at a time into boiling water, till I had obtained a solution of the requisite degree of consistency. I passed it through a linen cloth, and then mixed it with a boiling solution of subnitrate of lead, which I added in excess, and with which I digested the precipitate for a long time, that no part of the starch might remain uncombined. I then washed the precipitate by boiling it repeatedly in water, till that liquid ceased to take up any more subnitrate of lead. I then subjected it to pressure, and dried it in a vacuum in the temperature of 212°. his amylate, when analyzed by combustion, left 28 per cent. of oxide of lead. Hence it is composed of Starch..... 72..... 100 28 100 38.89 These 38.89 parts of oxide of lead contain 2.78 of oxygen. I endeavoured, likewise, to form an amylate containing more base. I found that such a compound exists, though I was not possessed of any method of separating it in a state of purity. We form it by mixing ammonia with a boiling solution of starch, and precipitating the mixture by a boiling solution of subnitrate of lead. But we cannot (unless by pure accident) find the point at which no neutral amylate is formed, or no subnitrate of the last degree. A subamylate, which I endeavoured to obtain as near the point of supersaturation as possible, without being mixed with insoluble subnitrate, gave by combustion half its weight of oxide of lead; so that it seems to contain the starch combined with three times as much base as in the neutral amylate. 0.4 of starch, dried in a vacuum, gave by combustion 0.2405 water, and 0-6395 carbonic acid, equivalent to 7064 per cent. of hydrogen, and 43.481 of carbon. 0.555 of amylate of lead, equivalent to 0.4 of starch, produced by combustion 0.239 water, and 0·643 carbonic acid, which gives us per cent. 7.023 hydrogen, and 43-724 carbon. It appears then that starch dried in a vacuum does not retain any water. starch then is composed of Potatoe But we find that in amylate of lead the starch contains 18 times as much oxygen as the base, and in the subamylate six times as much. For 2.78 x 18 = 50·04, which differs very little from 49.455. Starch then contains either six or 18 atoms of oxygen. It is therefore composed of 6 0 + 7 C + 13 H, or of 18 O + 21 C + 39 H. According to this statement, its composition should be This agrees well with the analytical result. 7.090 43.327 49.583 Thenard and Gay-Lussac found wheat starch composed of 677 hydrogen, 43.55 carbon, and 49.68 oxygen. 20 parts of starch, when incinerated in a platinum crucible, furnish 0.046 of ashes, consisting entirely of the earthy phosphates. Of course they ap pear to have been only mechanically mixed with the starch; but if they be chemically combined, it is difficult to determine the relation of their elementary atoms to those of the primary elements. Before finishing this first set of experiments on the chemical proportions in organic nature, I shall make some observations relative to the substances which have come under our review. As to the number of elementary atoms of which an organic atom is composed, it does not seem necessary that the most simple ratio between the elements should express that number. Thus it does not seem necessary that an atom of starch ought to contain 6 0 + 7C+ 13 H, or 26 elementary atoms; it is just as possible that it contains three times that number, and that it is upon such a composition that the proportion between the starch and oxide of lead in the neutral amylate depends. In the same way, we may say, that gallic acid is composed of 3 0 + 6C + 6 H, and not of O + 2 C 2 H. The great number of elementary atoms combined in a compound atom does not constitute any objection to this conclusion; for if the atom of starch contains in fact 78 elementary atoms, we may, on the other side, point out in organic nature compound atoms of the second and third order, which contain a still greater number of elements. Thus the atom of crystallized alum contains one atom of potassium, two of aluminium, eight of sulphur, 80 of oxygen, and 96 of hydrogen, constituting altogether VOL. V. N° IV. S 187 elementary atoms: or, even supposing potash to contain only one atom of oxygen, the atom of crystallized alum will still contain 94 elementary atoms. The organic atoms must be much larger than those of the first order in organic nature: hence the reason why their capacity of saturation is in general so small. It is well known that sugar of milk and gum arabic form mucous acid when treated with nitric acid, while sugar and starch do not furnish any of this acid. In the two first the hydrogen has to the oxygen the same ratio as in water. The two last contain hydrogen in excess. Sugar of milk is composed of...... 80+ 10 C + 16 H 80 + 6 C + 10 H If from the first you take 4 C + 6 H, you obtain the second. In the same manner, by taking from two atoms of gum arabic 4 C + 9 H, you will leave three atoms of mucous acid. As to sugar and starch, if you represent the first as containing 20 atoms of oxygen, and the last as containing 18 atoms, we shall find it impossible to form mucous acid without taking away some atoms of oxygen. We may then form the idea that the organic atoms have a certain mechanical structure, which enables us to deprive some of them of certain elementary atoms without altering the whole very much. In this way we remove certain atoms of sugar of milk, and there remains mucous acid. If we continue to remove other atoms, this acid is likewise destroyed, and the whole reduced to the common products of the decomposition of the ternary oxides, namely, oxalic and malic acids. The construction of the atom of common sugar is such that, as soon as you take away the first elementary atom, it separates (so to speak) into oxalic and malic acids. It is only by such a structure that we can explain the different products from the action of nitric acid on the ternary oxides, composed of the same elements, and in proportions (stated in per cents.) but little different from each other. I am persuaded that an attempt to study the probabilities of the construction of organic atoms, nearly in the same way as Dr. Wollaston endeavoured to represent the composition of boracite, by means of differently coloured balls-I am persuaded, I say, that such a study would be of the greatest importance, and might be even capable of correcting analysis; as analysis might probably indicate a number of elementary atoms, incapable of forming any regular figure whatever. If we were acquainted with the composition of alcohol, and of several varieties of sugar, the theory of fermentation would follow as a consequence from this knowledge. It is natural to suppose that fermentation is a very simple operation, and that it connects merely in the formation of carbonic acid gas, from the carbon of the sugar uniting partly with the oxygen of the sugar, and partly |