ARTICLE IV. On a new Variety of Ulmin. By Thomas Thomson, M. D. F. R.S. THE experiments detailed in the first number of these Annals upon the ulmin from the elm show us that it is a peculiar vegetable principle, distinguished by the following properties:1. Of a dark brown colour, and little taste. 2. Soluble in water, but insoluble in alcohol and ether. 3. Not precipitated by solution of gelatine. 4. Precipitated brown by iron, tin, mercury, and lead, when these metals are in the state of saline solutions. 5. Precipitated by acids. 6. Swells greatly when heated, as is the case with gum, but does not melt. These characters do not apply to any other vegetable principle at present known. Hence it is obvious that we must constitute this substance a new vegetable principle. Some chemists are inclined to refer ulmin to extractive; but it is high time to render that very indefinite class of vegetable substances somewhat more precise. Nobody has ever examined extractive in a state of purity. Hence its properties are unknown, and it has been customary to refer to that class all substances which could not be referred to any other. It constitutes a kind of sirk, or common sewer, in vegetable chemistry; but such an indefinite mode of proceeding is highly injurious to the progress of this branch of the science. If we wish to make ourselves accurately acquainted with the vegetable kingdom, we must distinguish every substance which possesses peculiar properties by a peculiar name. No risk of error results from multiplying the number of vegetable principles: the error into which we are most likely to run is classing the most dissimilar substances under the same name; thus enabling us to satisfy ourselves and others with giving a substance a name without being in the least aware of its distinguishing characters. What, for example, could be more preposterous than to give the same name to vegetable substances, some of which are soluble, and some insoluble, in alcohol? Yet this has been proposed by some of the most eminent chemists, both in this country and on the continent. Now that the vegetable principle which constitutes the subject of this article has been distinguished by a name, and that the attention of men of science and observation has been turned to it, we may expect to find different species of it exuding from different species of trees besides the elm. The variety which I am going to describe is an example of this. I got it from Mr. Sowerby, who informed me that he collected it from the oak. It possesses the following properties, which distinguish it from the ulmin of the elm : 1. Its colour is a very dark brown, almost black, and it leaves a chocolate coloured stain on paper. It readily crumbles to powder between the fingers. Lustre, resinous. Taste, more astringent than the ulmin from the elm, and inclining to bitter. 2. Dissolves readily in water. The colour of the solution is dark brown, and so intense as to be opake. When left to spontaneous evaporation upon a watch-glass the ulmin remains, divided into a great number of minute portions by sections, which issue in rays from the centre, and the ulmin adheres but weakly to the glass. 3. Insoluble in alcohol and ether. 4. When the aqueous solution is dropped into alcohol of the specific gravity 0 809, brown flocks precipitate, but the alcohol retains a brown colour, and of course a portion of the ulmin remains in solution. 5. The aqueous solution is not precipitated by the solution of gelatine in water. 6. Some of the precipitates which the aqueous solution of this variety of ulmin forms with the metalline salts differ in colour from the precipitates formed by the ulmin from the elm. The following were the metalline salts tried: (1.) Sulphate of iron is thrown down dark green, and the colour is permanent, though the liquid be left 24 hours in an open glass. (2.) Sulphate of copper is precipitated also green. (3.) Sulphate of zinc is precipitated brown, and the colour of the precipitate speedily deepens, and becomes at last a dirty black. (4.) Nitrate of silver is precipitated in brown flocks. (5.) Acetate of lead is precipitated in brown flocks. 7. The aqueous solution is precipitated in brown flocks by a few drops of nitric acid. This solution being evaporated to dryness in a watch-glass, a yellow tasteless powder remained, insoluble in alcohol, but soluble in water. This powder was charred at a very moderate heat; owing probably to the action of the nitric acid which it still retained. Acetic acid does not precipitate this variety of ulmin from water. 8. Neither potash, carbonate of potash, nor ammonia, precipitate it from water. 9. When exposed to heat it swells up like gum, and readily burns away before the blow-pipe, leaving behind it a minute portion of white matter, which did not melt by the continuation of the heat. This matter dissolved with effervescence in nitric acid, except some hardly perceptible flocks, which had the aspect of silica, but were too minute to be subjected to a chemical examination. The addition of ammonia to the nitric acid solution occasions the separation of a few flocks, which redissolve by agitation. Carbonate of potash occasions a more copious precipitate. Hence it would appear that the ash consists of carbonate of lime, with some traces of magnesia and silica. This variety of ulmin resembles the bitter principle from coffee described by Chenevix, and the tannin of Kino, in striking a green colour with sulphate of iron. Its effect upon sulphate of zinc I consider as its most remarkable property. Zinc is usually precipitated of a white colour from its solutions; but the ulmin of the oak throws it down almost black. The appearance of the ulmin of the oak, its taste, and the tree from which it was obtained, led me to expect that it would contain tannin; but if not forming a precipitate with gelatine be characteristic of the absence of that principle, as we consider it at present, we must conclude that the ulmin of the oak contains no tannin whatever. Mr. Sowerby likewise collected ulmin from the hornbeam; but as he unfortunately mixed it with ulmin from the elm, it was not possible to determine its peculiar characters. I mention the circumstance to induce such of my readers as are interested in the progress of vegetable chemistry, and have an opportunity of examining the trunks of trees, to look for exudations from them, that we may have information as speedily as possible of the various trees that yield this hitherto neglected vegetable principle. ARTICLE V. On Sir H. Davy's Theory of Chlorine, and its Compounds.* By Mr. William Henderson, Member of the Royal Medical Society of Edinburgh. THE reasons which may be alleged in proof of the simple nature of oxymuriatic gas seem easily reducible to four heads, viz. : I. It is converted into muriatic acid by union with bydrogen; and this change is unaccompanied by the evolution of any aqueous vapour. 11. The products of its action on combustibles, and on metals, differ essentially from those which arise from the action of oxygen on the same bodies. *This essay was honoured with the prize medal of the Medical Society of Edinburgh for 1812, III. It cannot, when perfectly dry, be made to act on, or unite with, charcoal. IV. In most, if not in all cases of its evolution, a portion of water is formed. Each of these will be the subject of separate examination. 1. Of the conversion of Oxymuriatic Gas into Muriatic Acid, by the action of Hydrogen. It is stated in Dr. Thomson's System of Chemistry,* that water is an essential ingredient of muriatic acid; and that, hitherto, all attempts to procure it in an insulated elastic form have failed. M. Berthollet remarks, that, after having been exposed to a cold equal to 10° of Fahrenheit's scale, the proportion of real acid was to the water as 26.6 to 34.9.† This proportion, as Dr. T. observes, is probably excessive; but it must be noted that the means employed by Berthollet were not adequatè to the condensation of water held in the elastic form by an affinity so powerful as that between the muriatic acid and its water appears to be. Dr. Thomson considers the proportion of 25 per cent. given by MM. Gay-Lussac and Thenard, as being probably near the truth. Mr. Dalton is, however, inclined to believe that muriatic acid gas contains no aqueous vapour; and the reasoning employed by him is to the following effect. § If oxygen, hydrogen, nitrogen, or any of the other gases which are not readily, and in considerable quantity, absorbed by water, be brought into contact with that fluid, the vaporific force of the heat to which they may be exposed will raise a portion of it into the interstices of their particles; but if fluoric, muriatic, sulphuric, or nitric acid, in the state of gas, be placed in similar circumstances, an attraction is exerted between it and the water; in consequence of which the acid assumes the liquid form. "Hence," adds Mr. Dalton, "it should seem that these acid gases, so far from obstinately retaining their vapour, as is commonly imagined, cannot be induced to admit any vapour at all, in ordinary circumstances." This reasoning is very plausible, and certainly highly ingenious; but it seems to me not unobjectionable. The gas experimented on by Mr. Dalton was of necessity previously saturated with aqueous vapour; and,, therefore, could not admit into its constitution an additional quantity. No one would hazard the assertion that muriate of lime contains no water of crystallization, assigning as a reason, that, if a very small portion of water be added to the crystals of this salt-they assume the liquid form. Yet it appears to me * Vol. v. p. 778. + Troisième Suite des Recherches sur les Lois de l'Affinité, p. 103, &c. that this assertion and proof would be exactly analogous to those offered by Mr. Dalton. Since, then, unless we adopt the recent views of Sir H. Davy, his experiments, in conjunction with those of Dr Henry, † MM. Gay-Lussac and Thenard, M. Berthollet, § Mr. Murray, and Dr. Bostock,** may be looked on as proving satisfactorily the existence of water in muriatic acid gas; let us examine the relation, in regard to quantity, subsisting between it and the oxygen, which oxymuriatic gas used to be supposed to contain. According to the analysis of Chenevix, ++ oxymuriatic gas consists of 77.5 of muriatic acid, united to 22.5 of oxygen by weight. If to this compound a quantity of hydrogen be added, and if the mixture be then exposed to the sun's light, muriatic acid is produced. In Mr. Dalton's detail of his experiments on this subject (which are by far the most complete set that have. fallen under my notice), he mentions that he always employed a quantity of water to condense the residual muriatic acid: he could not, of course, easily ascertain whether or not any water was evolved along with the acid. By calculation, I am led to believe there was not: for 22.5 of oxygen are capable of forming, by union with 3.76479 of hydrogen, a quantity of water equal to 26 26479, which approaches singularly near to the estimate of MM. Gay-Lussac and Thenard; and which may acquire some additional probability from the circumstance that all others who have experimented on the quantity of water in this gas, have stated it as being greater than that which is assigned by these chemists. ‡‡ Let us pursue the subject a little farther. Mr. Dalton, speaking of the quantity of hydrogen necessary to decompose oxymuriatic gas, says, "From the mean of five experiments, I am induced to conclude, that 100 measures of hydrogen require 94 measures of oxymuriatic acid gas. In every one of the experiments the acid was less than the hydrogen."§§ I have already stated that 3.76479 of hydrogen are sufficient to unite with the oxygen which 100 of oxymuriatic gas has been thought to contain. Now 3-76479 grs. of hydrogen occupy, according to * Phil. Trans. 1809, p. 92, 458. + Nicholson's Journal, 4to. vol. iv. p. 247. Rech. Phys. Chim. tome ii. p. 94, &c. Journal de Physique, tome Ixiv. p. 196. Nicholson's Journal, vol. xxxi. p. 123, &c. **Nicholson's Journal, vol. xxxii. ++ See Thomson's Syst. vol. ii. p. 257. It may not be unworthy of notice that 1 cubic inch of hydrogen, by union with very nearly 2 inches of oxygen, forms a quantity of water, whose weight is to that of the real muriatic acid contained in 2 inches of the acid gas, as 26 to 100. New System, p. 307, |