Chemical Experiments on Guaiacum

IV. Chemical Experiments on Guaiacum. By Mr. William Brande. Communicated by Charles Hatchett, Esq. F.R.S. Read December 19, 1805. Among the numerous substances which are comprehended under the name of resins, there is perhaps no one which possesses so many curious properties, as that now under consideration; and it is remarkable that no more attention has been paid to the subject, since many of the alterations which it undergoes when treated with different solvents, have been mentioned by various authors. § I. Guaiacum has a green hue externally; is in some degree transparent; and breaks with a vitreous fracture. When pulverised it is of a gray colour, but gradually becomes greenish on exposure to air. It melts when heated, and diffuses at the same time a pungent aromatic odour. It has when in powder a pleasant balsamic smell, but scarcely any taste, although when swallowed it excites a very powerful burning sensation in the throat. Its specific gravity is 1.2289. MDCCCVI. § II. 1. When pulverised guaiacum is digested in a moderate heat with distilled water, an opaque solution is formed, which becomes clear on passing the whole through a filter. The filtrated liquor is of a greenish-brown colour; it has a peculiar smell, and a sweetish taste. It leaves on evaporation a brown substance, which is soluble in alcohol, nearly soluble in boiling water, and very little acted upon by sulphuric ether. This solution was examined by the following re-agents. Muriate of alumina occasioned a brown insoluble precipitate after some hours had elapsed. Muriate of tin formed a brown flaky precipitate under the same circumstances. Nitrate of silver gave a copious brown precipitate. Suspecting the presence of lime in the solution, I added a few drops of oxalate of ammonia, when the liquid immediately became turbid, and deposited brown flakes, which, after having been treated with boiling alcohol, yielded traces of oxalate of lime. These effects, therefore, indicate the presence of a substance in guaiacum, which possesses the properties of extract;* the action of the reagent is however somewhat modified, by a small quantity of lime which is also in solution. One hundred grains of guaiacum yielded about nine grains of this impure extractive matter. * By the term extract, I mean that substance, which by chemists is called the Extractive Principle of Vegetables. Vide Thomson's Syst. of Chemistry, 2d edit. Vol. IV. p. 276. Alcohol dissolves guaiacum with facility, leaving some extraneous matter, which generally amounts to about 5 per cent. This solution is of a deep brown colour; the addition of water separates the resin, forming a milky fluid which passes the filter. Acids produce the following changes: A. Muriatic acid throws down an ash-coloured precipitate, which is not re-dissolved by heating the mixture. In this case the resin appears but little altered. B. Liquid oxy-muriatic acid when poured into this solution, forms a precipitate of a very beautiful pale-blue colour, which may be preserved unaltered. C. Sulphuric acid, when not added in too large a quantity, separates the resin of a pale green colour. D. Acetic acid does not form any precipitate. This acid is indeed capable of dissolving most of the resins. E. Nitric acid diluted with one-fourth of its weight of water, causes no precipitate till after the period of some hours. The liquid at first assumes a green colour, and if water be added at this period, a green precipitate may be obtained; the green colour soon changes to blue, (when by the same means a blue precipitate may be obtained;) it then becomes brown, and a brown precipitate spontaneously makes its appearance, the properties of which will be afterwards mentioned. The changes of colour produced by nitric, and oxy-muriatic acids, in the alcoholic solution, are very remarkable, and I believe peculiar to guaiacum: there is moreover much reason to suppose that the above alterations in colour are occasioned by oxygen.* It likewise appears from that which has been stated, that the blue and green oxides (if they may be so called by way of distinction) are soluble in the mixture of nitric acid and alcohol, while the brown precipitate is insoluble. F. Alkalis do not form any precipitate when added to the solution of guaiacum in alcohol. 3. Guaiacum is less soluble in sulphuric ether than in alcohol; the properties of this solution nearly coincide with those just mentioned. 4. Muriatic acid dissolves a small portion of guaiacum, the solution assuming a deep brown colour; but if heat be applied, the resin melts into a blackish mass, preventing any farther action from taking place. 5. Sulphuric acid forms with guaiacum a deep red liquid, which, when fresh prepared, deposits a lilac coloured precipitate on the addition of water; a precipitate is also formed * The following experiments appear to verify this supposition: Fifty grains of freshly pulverised guaiacum were introduced into a glass jar containing 60 cubic inches of oxy-muriatic acid gas. The resin speedily assumed a brown colour, having passed through several shades of green and blue. Liquid ammonia was poured on this brown substance, while yet immersed in the acid; the whole became green; it therefore seemed thus to be deprived of part of the oxygen which it apparently had acquired by the preceding experiment. An equal portion of the same guaiacum was exposed under similar circumstances to the action of oxy-muriatic acid, excepting that the glass in which the experiment was made, was covered with a black varnish, and placed in a dark apartment. On examining the result of this experiment, the resin was found to have undergone precisely the same changes as when exposed to light. Ammonia had also the same effect. Guaiacum was also exposed over mercury to oxygen gas; the resin assumed after some days the green colour which a longer exposure to the atmosphere produces: this change was likewise found by a second experiment to be effected without the presence of light. by the alkalis. If heat be employed in forming this solution, the resin is speedily decomposed; and if the whole of the acid be evaporated, there remains a black coaly substance, together with some sulphate of lime. 6. Nitric acid appears to exert a more powerful action on guaiacum than on any of the resinous bodies. 100 grains of pure guaiacum previously reduced to powder, were cautiously added to two ounces of nitric acid, of the specific gravity of 1.39. The resin at first assumed a dark green colour, a violent effervescence was produced, attended with the emission of much nitrous gas, and the whole was dissolved without the assistance of heat, which is not the case with the resins in general, for when these bodies are thus treated with nitric acid, they are commonly converted into an orange-coloured porous mass. The solution thus formed, yielded while recent, a brown precipitate with the alkalis, which was redissolved on the application of heat, forming a deep brown liquid. Muriatic acid also separated the guaiacum from this solution, not however without having undergone some change. Sulphuric acid caused no precipitate. After this solution of guaiacum in nitric acid had remained undisturbed for some hours, a considerable proportion of crystallised oxalic acid was deposited. When guaiacum was treated with dilute nitric acid, the results were somewhat different. A slight effervescence took place, and part of the resin was dissolved, the remainder being converted into a brown substance, resembling the precipitate obtained from the alcoholic solution as above mentioned. (2. E.) This brown substance appears to be guaiacum, the properties of which are materially altered, by its combination with oxygen; and I am led to think that the changes of colour produced by nitric and oxy-muriatic acids, are the consequence of the different proportions of oxygen with which the guaiacum has been united; for we know that the colours of metallic, and many other bodies, are greatly influenced by the same cause. The brown substance was separated by filtration; the filtrated liquor yielded yellow flocculent precipitates with the alkalis, and on examination was found to hold nitrate of lime in solution. The undissolved portion was of a deep chocolate-brown colour. A similar substance may also be obtained, by evaporating the recent nitric solution to dryness, taking care not to apply too much heat towards the end of the process. The substance obtained by either of these means, possesses the properties of a resin in greater perfection than guaiacum; it is equally soluble in alcohol and sulphuric ether, insoluble in water, &c.; but when burned it emits a peculiar smell, more resembling animal than vegetable bodies. If, however, fresh portions of nitric acid be added three or four times successively; or if a large quantity be employed to form the solution; the product obtained by evaporation is then of a very different nature; for it has lost all the characteristic properties of a resin, having become equally soluble in water and alcohol; the solution of it in this state having an astringent bitter taste.* * Vide Mr. Hatchett's two Papers on an artificial Substance which possesses the principal characteristic Properties of Tannin. Phil.Trans. 1805, p. 211, and 285. 7. Guaiacum is copiously soluble in the pure and carbonated alkalis, forming greenish-brown liquids. Two ounces of a saturated solution of caustic potash took up rather more than 65 grains of the resin; the same quantity of liquid ammonia dissolved only 25 grains. Nitric acid formed in these solutions a deep brown precipitate, the shades of which varied according to the quantity of acid which had been employed. This precipitate was found on examination to possess the properties of that formed by nitric acid in the solution of guaiacum (2. E.) in alcohol. Dilute sulphuric acid, when poured into any of the above alkaline solutions, formed a flesh-coloured curdy precipitate. Muriatic acid produced the same effect. The two last mentioned precipitates differ from guaiacum, in being less acted upon by sulphuric ether and more soluble in boiling water, their properties therefore approach nearer to extract. Moreover, when these precipitates were redissolved in ammonia, and were again separated by muriatic acid, the above mentioned properties became more evident. § III. 100 grains of very pure guaiacum in powder, were put into a glass retort, to which the usual apparatus was adapted. The distillation was gradually performed on an open fire, until the bottom of the retort became red hot. The following products were obtained: | Product | Grains | |----------------------------------------------|--------| | Acidulated water | 5.5 | | Thick brown oil, becoming turbid on cooling | 24.5 | | Thin empyreumatic oil | 30.0 | | Coal remaining in the retort | 30.5 | | Mixed gases, consisting chiefly of carbonic acid and carbonated hydrogen | 9.0 | Total: 99.5 The coal, amounting to 30.5 grains, yielded on incineration 3 grains of lime. To discover whether any fixed alkali was present, 200 grains of the purest guaiacum (that in drops) were reduced to ashes; these were dissolved in muriatic acid, and precipitated by ammonia; the whole was then filtrated, and the clear liquor evaporated to dryness, but not any trace of a neutral salt with a basis of fixed alkali was perceptible. § IV. From the action of different solvents on guaiacum, it appears, that although this substance possesses many properties in common with resinous bodies, it nevertheless differs from them in the following particulars: 1. By affording a portion of vegetable extract. 2. By the curious alterations which it undergoes when subjected to the action of bodies, which readily communicate oxygen, such as nitric and oxy-muriatic acids; and the rapidity with which it dissolves in the former. 3. By being converted into a more perfect resin; in which respect guaiacum bears some resemblance to the green resin which constitutes the colouring matter of the leaves of trees, &c.* 4. By yielding oxalic acid. 5. By the quantity of charcoal and lime which are obtained from it when subjected to destructive distillation. § V. From the whole therefore of the above mentioned properties, it evidently appears that guaiacum is a substance very different from those which are denominated resins, and that it is also different from all those which are enumerated amongst the balsams, gum resins, gums, and extracts: most probably it is a substance distinct in its nature from any of the above, in consequence of certain peculiarities in the proportions and chemical combination of its constituent elementary principles; but as this opinion may be thought not sufficiently supported by the facts which have been adduced, we may for the present be allowed to regard guaiacum as composed of a resin modified by the vegetable extractive * This substance was found by Proust to be insoluble in water, and soluble in alcohol. When treated with oxy-muriatic acid, it assumed the colour of a withered leaf, acquiring the resinous properties in greater perfection. Vide Thomson's Syst. of Chemistry, 2d edit. Vol. IV. p. 318. MDCCCVI. principle, and as such, perhaps the definition of it by the term of an Extracto-Resin may be adopted without impropriety. P. S. I have observed that the action of oxygen on some of the other resinous bodies is very remarkable. It is well known that by digesting mastich in alcohol, a partial solution only is formed, and there remains an elastic substance, which is generally said to possess the properties of pure caoutchouc; it appears however to differ from this substance in becoming hard when dried by exposure to air. Moreover, I have remarked that the part of mastich which remains dissolved by alcohol, may be again precipitated by water, and, on examination, I found the precipitate to possess the properties of a pure resin: but when a stream of oxy-muriatic acid gas was made to pass through the solution, a tough elastic substance was thrown down, which became brittle when dried, and was soluble in boiling alcohol, but separated again as the solution cooled: its properties, therefore, somewhat approached to those of the original insoluble part.