Calcium Usnate. When pure usnic acid was moistened with spirit, and then rubbed up in a mortar with milk of lime, it combined and formed a deep yellow paste, which, on the addition of more water and filtration, yielded a lemon-coloured solution, containing calcium usnate, and hydrate. When this solution was heated it became turbid, and after boiling some time, the whole of the usnic acid was deposited as an insoluble calcium compound, in the form of small deep yellow rhomboidal crystals. Although I made several analyses of this compound, prepared at different times, I was unable to obtain it of a constant composition, probably owing to its being mixed with variable quantities of calcium carbonate and hydrate. The formation of this insoluble calcium salt is very characteristic of usnic acid, and is an excellent test of its presence. As with the sodium salt, carbonic anhydride entirely decomposes the calcium compound. Usnic acid appears, therefore, to be a very feeble acid. An attempt was made to prepare ethylic usnate by treating usnate of silver with ethylic iodide, but without success. When usnic acid was treated with bromine it was completely decomposed, and converted into an orange-coloured uncrystallizable resin. Evernia prunastri-Evernic Acid. The evernic and usnic acids that this lichen contains were extracted by the lime process, which consists in macerating the lichen two or three times successively with milk of lime for about half an hour each time. The solution of the mixed acids was then filtered, precipitated by a slight excess of hydrochloric acid, and the precipitate collected and dried. In order to extract the evernic acid from the mixture, it was agitated for about five minutes with four parts boiling alcohol and filtered. The acids remaining undissolved were treated two or three times with the same quantity of boiling alcohol, and the dissolved evernic acid precipitated by the addition of an equal bulk of water. By this means the evernic acid, being readily soluble in boiling alcohol, was in a great measure separated from the usnic acid, which dissolves with difficulty in that menstruum unless digested with it for a considerable time. The crude evernic acid thus obtained amounted to about one-third of the mixed acids, and was purified by repeated crystallization from strong spirit, taking care not to digest it for any length of time. The process is much facilitated by completely removing the mother liquors by Bunsen's vacuum filter. Pure evernic acid, as has been already described by myself* and Hesset, consists of aggregations of minute needles, melting at 164° C. It is a feeble acid, and does not decompose solutions of bicarbonate of sodium in the cold; as, however, the adhering colouring-matter is somewhat soluble in that menstruum, it may be employed to free the crude acid to a great * Ann. der Chem. und Pharm. vol. lxviii. p. 84. † Ibid. vol. cxvii. p. 298. extent from that impurity. The solution of calcium evernate is decomposed by a long-continued current of carbonic anhydride, which precipitates calcic carbonate and unaltered evernic acid. On theoretical grounds it has been stated* that, by the action of potassic or baric hydrate, evernic acid should be resolved into orsellinic and everninic acids. This prediction, however, is incorrect, as I find, as formerly stated, that everninic acid is the only fixed product. Tetrabrom-evernic Acid. Perfectly dry and finely powdered evernic acid was treated in the cold with a slight excess of dry bromine, large quantities of hydrobromic acid were given off, and a brominated compound produced. In order to prevent any portion of the acid escaping bromination, the product was finely powdered and again treated with bromine. After standing some time to allow the excess of bromine to volatilize, the finely powdered compound was well washed with bisulphide of carbon, to remove the last traces of bromine, and a small quantity of a resinous body which is produced at the same time. Two or three crystallizations from boiling spirit render it quite pure. When subjected to analysis, it gave the following results: I. 312 grm. acid gave 362 grm.carbonic anhydride and '067 grm. water. II. 321 grm. acid gave 373 grm. bromide of silver. 12 This analysis agrees very well with the formula C,, H1, Br, O., four equivalents of hydrogen in evernic acid being replaced by bromine. Tetrabrom-evernic acid is rather soluble in hot alcohol, from which it crystallizes on standing some time in small colourless prisms. It is insoluble in water and bisulphide of carbon, slightly soluble in hot benzol, and readily in ether, which when quickly evaporated leaves it as a transparent colourless resin; it melts at 161° C. The acid is very soluble in alkaline solutions, which on evaporation dry up to a gummy mass. When heated with concentrated sulphuric acid it decomposes. Usnic Acid from Evernia prunastri. The usnic acid left undissolved in the preparation of evernic acid usually retained traces of that acid even after repeated treatment with alcohol; but this was entirely removed by boiling with lime, as described in the first part of this paper. This decomposed and removed the evernic acid and other impurities, leaving the usnic acid in the form of an insoluble calcium * Watts's Dict. Chem. vol. ii. p. 611.! † Ann. der Chem. und Pharm, vol. lxviii. p. 86. salt. The acid when freed from lime and purified, melted at 20 2o C., and by analysis gave the following results : I. 409 grm. usnic acid gave 939 grm. carbonic anhydride and 188 grm. water. From the above analyses it will be seen that the usnic acid from Evernia prunastri is identical in composition with that from Usnea barbata. It has the same melting-point, and agrees with it in all its other properties. Cladonia rangiferina. In 1848 I extracted the lichen acid from Cladonia rangiferina, and by analysis found it to have the same composition as usnic acid, with which it agrees very closely in its properties. Hesse, however, observed that this acid had a different melting-point (175° C.) from ordinary usnic acid (203° C.), and proposed, therefore, as it so closely resembled ordinary usnic acid in its general character, to call it ẞ-usnic acid. Cladonic Acid, ß-orcin. I formerly obtained‡ ß-orcin by subjecting to destructive distillation a mixture of the acids from Cladonia rangiferina and various species of Usnea; but I have lately found that ordinary usnic acid, melting at 203° C., obtained from Evernia prunastri, Ramalina calicaris, and the various Usneas, does not yield a trace of ß-orcin when distilled, whilst, on the contrary, the acid extracted from Cladonia (Hesse's ẞ-usnic acid melting at 175° C.), on being subjected to the same treatment, yields ẞ-orcin, thus showing a marked difference in the products of its decomposition from ordinary usnic acid, as well as in its melting-point. Under these circumstances, therefore, I think that it would be better to name the acid from Cladonia rangiferina "Cladonic Acid," instead of ß-usnic acid, as proposed by Hesse. I expected to have been able to subject cladonic acid to a more careful examination, and procured for that purpose a quantity of Cladonia rangiferina from the neighbourhood of Moffat. Unfortunately, however, it was not gathered until the beginning of December, and I was surprised to find that it contained scarcely a trace of cladonic or any similar acid. I intend to obtain a new quantity next summer, when I hope to be more successful. I cannot conclude this paper without acknowledging the efficient assistance I have received from Mr. Charles E. Groves. Ann. der Chem. und Pharm. vol. lxviii. p. 98. Ibid. vol. lxviii. p. 104. II. "On the successive Action of Sodium and Iodide of Ethyl upon Acetic Ether." By E. FRANKLAND, F.R.S., and B. F. DUPPA, Esq., F.R.S. Received January 13, 1870. In a paper by Mr. J. Alfred Wanklyn, bearing the above title, and published in the Proceedings of the Royal Society, vol. xviii. p. 91, the author refers to our memoir on the same subject printed in the Philosophical Transactions for 1866, vol. clvi. p. 37, and expresses his opinion that our interpretation of the nature of the reaction must be erroneous because it involves the disengagement of hydrogen. This opinion is founded upon certain experiments which Mr. Wanklyn has himself made, and which are described in the number of Liebig's Annalen' for January 1869, and in the Chemical Society's Journal, vol. ii. p. 371. In reference to this opinion we have to remark, first, that it is founded upon experiments which differ essentially from our own; and, second, that even the results obtained in those experiments by the author do not warrant the conclusion, at variance with ours, which he has drawn from them, viz. that the evolution of hydrogen in this reaction is inadmissible. The reaction, the theoretical explanation of which Mr. Wanklyn seeks to controvert, is described in the Philosophical Transactions, vol. clvi. p. 38, as follows:- -"When acetic ether is placed in contact with sodium it becomes hot, and a considerable quantity of gas is evolved, which, after being passed first through alcohol and then through water, burns with a nonluminous flame, and the products of combustion do not produce the slightest turbidity on agitation with baryta-water. In fact the gas is pure hydrogen. When the action is complete, the liquid solidifies on cooling to a mass resembling yellow beeswax. By putting the sodium into the acetic ether as just described, it is difficult to conduct the operation to completion, owing to the liquid gradually assuming such a thick and pasty condition as to prevent the further action of the sodium." Owing to the difficulty of carrying the reaction far enough in this way we frequently employed a modification of this process, which is minutely described in the same memoir. The modification consisted in placing the sodium in a separate vessel and causing the acetic ether to distil continuously over it; thus the portions of acetic ether still unacted upon were brought, again and again, into contact with the sodium, whilst the non-volatile product of the operation was retained in a lower vessel. As we acted upon several pounds of acetic ether at once, the operation frequently lasted several days, and during the whole time torrents of hydrogen were evolved. The temperature of the liquid in the distillation vessel was allowed to rise to 130° C., and the amount of sodium consumed was not much less than one atom for each molecule of acetic ether employed. We have made several attempts to determine quantitatively the volume of hydrogen given off from a known weight of sodium, and also from & known weight of acetic ether, but in neither operation could we obtain a trustworthy result. In the first case because the sodium, which fuses. during the reaction, breaks up into a vast number of very minute globules, the final disappearance of which in the highly coloured and pasty product it is impossible to verify. In the second case because the thickening of the liquid prevents the reaction being pushed far enough to decompose the whole of the acetic ether employed. In a quantitative experiment, in which 4.857 grammes of acetic ether were acted upon by sodium in slight excess, 344.79 cub. centims. of hydrogen at 0° C. and 760 millims. pressure were obtained. If one molecule of acetic ether had lost one atom of hydrogen, 615.9 cub. centims. of gas ought to have been collected. It was evident, however, that a large proportion of acetic ether still remained unattacked at the close of the experiment. Such, then, was our mode of operating; the hydrogen evolved was allowed freely to escape, the whole process was conducted at the ordinary atmospheric pressure, and the temperature varied from the boiling-point of acetic ether to 130° C. Moreover the acetic ether used was prepared with the greatest care so as to ensure the absence of alcohol and water. By our method of preparation, described in the memoir already cited, no traces of the former could be detected even in the crude ether; nevertheless it was first placed for several days over fragments of fused calcic chloride, which apparently remained perfectly dry and unaffected; it was then in some cases boiled for ten days or a fortnight upon many pounds of sodiumamalgam, which we find to be entirely without action upon pure acetic ether, whilst it rapidly attacks and removes alcohol, if the latter be added even in very small proportion to the acetic ether. When acetic ether, so treated and then distilled from the sodium-amalgam, was brought into contact with the sodium, an abundant evolution of hydrogen immediately commenced, and continued during the entire treatment, which, as already remarked, frequently lasted several days. The general impression, however, produced upon us by the whole of our operations was, that the evolution of hydrogen was not quite so great as that theoretically required by the reactions which we believe to take place; nevertheless it was obvious that no equations, from which free hydrogen was excluded, could possibly correctly express the chemical changes effected in this action. Certain experiments were undertaken to trace the missing hydrogen, but as they have not hitherto been completed we will not further allude to them here. We now turn to Mr. Wanklyn's mode of experimenting. This is not stated in his communication to the Royal Society, but is given in the Journal of the Chemical Society, vol. xvii. p. 371, and in the Ann. Chem. u. Pharm. for January 1869, as follows: Exp. 1. "I sealed up a quantity of sodium with acetate of ethyl, which had been very carefully deprived of alcohol and water, and weighed the tube containing these materials. I then heated the tube to 130° C. for some time, until the contents had changed from liquid to solid. After opening the tube and allowing any gas that might have formed to escape, I weighed it again. The loss amounted to 0·5 in 100 parts of acetic ether." |