ARTICLE III.

Experiments to determine the Definite Proportions in which the Elements of Organic Nature are combined. By Jacob Berzelius, M.D. F. R.S. Professor of Chemistry at Stockholm.

III. Analysis of the Ternary Oxides.

(Concluded from p. 184.)

Substances not Acid.—I mentioned before that the ternary oxides composed of carbon, hydrogen, and oxygen, have a strong tendency to combine with saline bases; and that in these combinations they act the part of acids. They possess the acid characters, however, in very different degrees. Many of them possess the property of combining at the same time with the strong acids, as is the case with tannin, and almost all the extractive and colouring matters. These oxides then are placed near the middle of the electro-chemical chain, and their affinities diminish in proportion as they approach the point of indifference of that chain. The only ternary oxide which contains nitricum, is a strong alkali; and the quaternary oxides, which contain nitricum, have likewise properties opposite to those of vegetable substances. They lie on the other side of the point of indifference of the electro-chemical chain; their tendency to unite with acids being more distinct than to combine with bases.

The ternary oxides already analyzed are all of a decided electronegative character, so that chemistry gives them the name of acids; if we except tannin, the acid properties of which are however very distinct.

It is known that the resins, fat oils, gums, extracts, &c., form insoluble compounds with various metallic oxides. These combinations are generally stated in such a manner in our Manuals of Chemistry, that a reader, whose attention is not specially directed towards these objects, considers these combinations as the only ones of which these organic bodies are capable: and, in fact, they are the only ones which are recognized by some striking property. These insoluble combinations of ternary oxides with binary oxides belonging to the class of salifiable bases, makes it probable that there exists a general affinity between these ternary oxides and bases. It is easy to convince ourselves of the truth of this suspicion by experiment.

Gum is precipitated by subacetate of lead, and sugar has the property of rendering lime more soluble in water. These facts were ascertained without the consequence being drawn from them, that these combinations owe their existence to a general affinity between saline bases and vegetable bodies, in consequence of which gum ought to have an affinity with lime and sugar for oxide of lead.

If we pour sugar into a solution of subacetate of lead, no precipitate takes place. But we should deceive ourselves, were we to conclude from this, that sugar does not combine with oxide of lead, or that it does not form an insoluble compound with that oxide. A solution of sugar not only dissolves oxide of lead; but by a long digestion it combines with an excess of that oxide, and forms an insoluble, light, white, and bulky compound. This compound dissolves in acetate of lead, subacetate of lead is formed, and the sugar is disengaged. I shall have occasion to speak more of this combination below. If we pour some drops of caustic ammonia into a solution of sugar of milk, we do not observe any change. The ammonia acts as a re-agent, just as if the sugar of milk were not present. We should deceive ourselves were we to conclude from this that sugar of milk and ammonia have no affinity for each other. We have only to macerate at the temperature of 122° a solution of sugar of milk with oxide of lead, and then to drop a little ammonia into the filtered liquid. This liquid, which is a combination of sugar of milk and oxide of lead, is decomposed, and an insoluble compound of sugar of milk with an excess of oxide of lead is precipitated. This precipitation is owing to the affinity of ammonia for sugar of milk, which it divides with the oxide of lead.

It is, in general, very difficult to obtain neutral combinations with these substances; at least unless this can be done when they are in solution in water, which has the same action on them as on the metallic oxides placed round the point of indifference of the electro-chemical chain; as the oxide of bismuth, antimony, tellurium, &c. We know that it is impossible to obtain a neutral muriate of these oxides, by treating them with liquid muriatic acid; we obtain only an insoluble submuriate and a soluble muriate with an enormous excess of acid. In the same manner when we digest a solution of common sugar, or sugar of milk, with oxide of lead, we obtain only an insoluble compound with an excess of oxide of lead, and a soluble combination with an enormous excess of sugar. If you pour ammonia into a solution of sugar, nothing indicates that the substances combine, and the ammonia evaporates from that solution as easily as from pure water. But if you expose sugar in powder to the action of ammoniacal gas, the sugar absorbs the gas, and forms with it a compound. Here the same thing takes place as when you expose oxide of antimony to the action of muriatic acid gas. These observations, I conceive, not only prove that the ternary vegetable oxides have a general tendency to combine with salifiable bases; but they point out also the reasons why this general tendency has hitherto remained unnoticed.

To be able to speak of these combinations it will be necessary to give them names, and I thought it would be agreeable to the principles of the chemical nomenclature to name, for example, a combination of sugar with oxide of lead, according to the different degrees of saturation, saccharate, sub-saccharate, super saccharate

of lead, In the same manner I shall use the terms gummates, amylates, saccolactates, to denote the combinations of gum, starch, sugar of milk with saline bases.

There is still a circumstance relative to the combination of the ternary oxides with the saline bases, which deserves to be mentioned here. An excess of these bases, especially the stronger ones, decomposes a great part of the ternary oxides in different ways, usually producing a great quantity of carbonic acid. The ternary oxides least exposed to this decomposition are these: 1. whose atoms of oxygen are equal in number to those of some one of the other elements, or surpass them in number: and 2. when the ratio of the hydrogen to the oxygen is less than in water. Such is the case with most of the acids analyzed. If the atoms of carbon and hydrogen surpass in number those of oxygen to a certain amount, the ternary oxide has a great tendency to undergo decomposition from the action of the salifiable bases. Such, for example, is the case with gallic acid, tannin; and, to a certain extent, with acetic acid. When, on the other hand, the atoms of each of the combustible elements surpass four or five times those of oxygen, the ternary oxide is more permanent: so that those oxides are best preserved which have either a great excess of combustible atoms or of oxygen. Of consequence, henzoic acid and the fat oils are but insensibly altered by the action of alkaline bodies.

This is the reason why, when the ternary oxides are gradually decomposed, either by the influence of air and water, or of acids, their atoms arrange themselves in such a manner as to form new products, in which, on one side, the oxygen is in excess, and, on the other, the atoms of the combustible elements greatly surpass those of the oxygen. Thus sugar is converted into carbonic acid and alcohol by fermentation; and gallic acid, by the influence of an alkali, yields on one side water and carbonic acid, and, on the other, an extractive matter abounding in carbon, to which it owes its dark colour. Perhaps it would be useful to class the ternary oxides into: 1, Oxides not easily decomposed in consequence of their excess of oxygen; such as oxalic, citric, tartaric acids, &c. 2. Oxides easily decomposed in consequence of the equilibrium of their elements, which is easily destroyed by a small force; such as tannin, gallic acid, sugar of milk, common sugar, &c. 3. Oxides not easily decomposed in consequence of the excess of their combustible atoms; such as benzoic acid, resins, fat oils, &c.

Let us now turn our attention more particularly to the ternary oxides destitute of acid properties.

10. Common Sugar.

I digested a solution of sugar with oxide of lead. At first the oxide dissolved, but after the digestion had been continued for some time, it was converted into a light white powder, by which the whole liquid was rendered opake. 1 separated the white powder

on a filter, washed it with boiling water, and dried it in a vacuum. This substance is a new combination of sugar and oxide of lead. It is quite insoluble in water, light, white, and destitute of taste. The acids, even carbonic acid gas, separate the sugar from it. When heated to a certain point it takes fire, and continues to burn of its own accord, leaving as a residuum oxide of lead mixed with metallic lead. It appears to contain no combined water. 1 have not been able to procure this substance quite free from carbonate of lead; but it is easy to determine how much of it is present by dissolving it in acetate of lead, which does not act upon the carbonate. By this means I found that in the subsaccharate of lead employed in my experiments, there was 1 per cent. of carbonate of lead; for 10 parts dissolved in acetate of lead left 0.15 of carbonate of lead undissolved.

Two parts of the subsaccharate of lead, when burnt, left 1.1728 of oxide of lead; but we must subtract 0.03 for carbonate of lead, that is, 0.025 of oxide of lead, and 0.005 of carbonic acid. There remains 1.1478 for the oxide of lead, and 0.8222 for the sugar; so that the subsaccharate is composed of

I repeated this analysis several times, and the results varied between 138 and 140 of oxide combined with 100 of sugar. The reason of this variation seems to be the difficulty of discovering when the oxide of lead is entirely penetrated with sugar. When any of it remains uncombined, it is obvious that the analysis will give an excess of base. The oxygen of 139.6 of oxide of lead is 9.98.

If we digest the above-mentioned subsaccharate in a solution of sugar, a part of it dissolves, and forms a clear liquid, with a slightly yellow colour, which contains lead. But the quantity of this metal is very small when compared with that of the sugar, of which the solution appears to contain an excess in the form of super-saccharate. When evaporated it leaves behind it a syrupy mass, which does not crystallize, and which attracts humidity from the atmosphere.

The crystalline form of sugar does not lead us to suspect that it contains water. I reduced it to a fine powder, and dried it in a vacuum. The loss of weight was only 0.1 per cent. I took ten parts of this sugar, and mixed them with 40 parts of yellow oxide of lead, reduced to a fine powder, and heated to redness afterwards. I digested this mixture in water, in the heat of a waterbath, till the oxide of lead had absorbed all the sugar. I then put it into a vacuum and dried it. The loss of weight was 0.53. I then heated it to 212° in a vacuum; but it sustained no farther loss of weight. This loss must have been water combined with the sugar; for, on dissolving the saccharate in nitric acid, not a single

bubble of carbonic acid gas made its escape. This shows that the sugar had not undergone decomposition. From this experiment it appears that sugar in its ordinary state is a compound of

But 5'6 of water contain 4.941 of oxygen, which is exactly the half of that found in the oxide of lead with which the sugar is combined in the sub-saccharate.

I took five parts of sugar dried in a vacuum, and put them into a small glass exactly weighed, the mouth of which was covered with paper. I put this glass in a jar over mercury, and then filled the jar with ammoniacal gas. The gas was slowly absorbed; the sugar contracted in bulk, and its surface acquired so strong a crystaЛline lustre as to appear humid. The saturated combination was a dense, coherent, flexible mass, which might be cut with a knife. It exhaled the odour of ammonia. The absorption of ammoniacal gas continued for four days; but I left the sugar in the gas 24 hours after it was saturated. It had gained 0.26 of its weight. This combination, which I consider as a neutral saccharate of ammonia, is composed of

But 5.49 ammonia contain 2.5 of oxygen, which is half the quantity that the water contains, and 4th of the oxygen in the oxide of lead.

0.4 of sugar dried in a vacuum, gave by combustion from 0.237 to 0.24 of water; and from 0.607 to 0.61 of carbonic acid gas. Hence it follows, that sugar is composed of

But we have seen that in these 100 parts of sugar there are 5.3 of water; containing 4.67725 oxygen. Now 4.67725 x 11 = 51-44975. Hence it follows, that the 94-7 parts of pure sugar contained ten times that quantity, or 46.7725, and consequently, that sugar contains ten times as much oxygen as the water, five times as much as the oxide of lead, and 20 times as much as the ammonia with which it was combined in the compounds mentioned above.