rior to that employed in the beginning of this century. The Engineer, he says, obferves, that fluices, which formerly stood 40 or 50 years, now laft only ten or a dozen. The Architect fees likewife with concern, that, notwithstanding all his attention in chufing timber of the best quality, in the conftruction of grand edifices, he finds himself, in the courfe of a few years, under the neceffity of fubftituting others in their room. He himself has feen veffels that had been built 40 years, and yet had the greateft part of their beams in a found ftate: whereas, in thofe of modern conftruction, the timbers evidently rot in the space of a few years. Indeed, the Author had formerly declared, in his Compleat Treatise on Forefts, that there is not at present a tree of a large fcantling to be found, that is not effentially distempered at its heart, or in which there is not at leaft a commencement of decay; which fometimes, indeed, is not perceptible, when the tree is first felled, but which will fhew itfelf in a very short space of time afterwards. Some have attributed this depravation of the wood in our times, to the great froft in 1709. The Author, though he allows this caufe to have had fome fhare in producing this effect, is of opinion that it is chiefly owing to other circumstances which he enumerates. The principal of these are, that for a very confiderable time paft, trees have been conftantly felled, and none planted in their room; that the timber now cut down is the refuse of our predeceffors; and that the trees in the major part of forefts are the produce of old ftumps and roots, vegetating in a foil almost intirely exhaufted. He Whatever be the caufe, or caufes, of this diminution in the ftrength of the modern timber, the Author obferves that it would be both erroneous and unfafe for the architect or shipbuilder to estimate its present strength, from the refult of the experiments made for that purpofe formerly by M. Parent and others. here relates fome trials made to determine the refiftance of large beams, at Breft, by the engineers at that place, under the direction of the commandant; the refults of which confirm the truth of the foregoing.obfervation, and evince the neceffity of eftimating the ftrength of modern timber by a new standard. In the last memoir of this clafs, which is of a local nature, M. Deparcieux proposes his ideas on the best expedients to prevent the inconveniences and dangers, which frequently enfue on the breaking up of the ice, in the river Seine. CHEMISTRY. CHEMISTRY. MEMOIR I. On the Caoutchouc, or the Elaflic Refin of Cayenne; and on the Discovery of a Method of diffolving it, without impairing or destroying its Properties. By M. Macquer *. The fubftance treated of in this article is in some respects one of the most fingular productions of the vegetable kingdom; both on account of its remarkable chemical qualities, and of its other still more interefting properties. As it appears to be very little known in this country, and as this very able Chemist has at length fucceeded in his repeated attempts to discover a perfect and innoxious folvent of this hetroclite fubftance, which had hitherto been ineffectually fought after by other chemists; we fhall dwell fomewhat largely on its hiftory, and properties, and on the method here indicated of compleatly diffolving it, and thereby rendering it a useful acquifition to the arts and to experimental philofophy. This refin, as it is called, has been hitherto brought from different parts of South America and Afia. Little however was known concerning it, (though fome utenfils and other works formed of it, by the natives of those countries that produce it, were preserved in the cabinets of the curious) till the return of the French Academicians, who were fent to measure the earth in Peru. Of thefe, Mr. Condamine particularly, in the relation of his voyage down the River of Amazons, first entered into fome detail concerning its origin, and the manner in which the Indians collect it, and form it, by means of earthen moulds, into various fhapes. From his and other accounts it appears that it is a milky exudation, or a kind of natural emulfion, flowing from incifions made in a certain tree. While in this liquid ftate, it receives from them the particular form intended to be given to it. The liquor foon dries, and acquires a folid confiftence; manifefting at the fame time a most extraordinary degree of flexibility and elasticity. It has indeed been faid that a ring of this fubftance, fo fmall as to fit the finger, would bear fuch a degree of extenfion as to become a girdle for the body, which, on being flipped off, would inflantly return to its former dimenfions; and that a ball of this refin, being dropped on the ground, would rebound to a greater height than that from which it fell †. The first affertion is un Our Readers are referred to a fhort account which we formerly gave [in our 37th volume, September 1767, page 164] of Mr. Heriffant's and the prefent Author's experiments on this fubftance, as fummarily related in the volume of thefe memoirs for the year 1763. Notwithfanding what we have there faid, it now appears, from this article, that at that time thefe two Chemifts had only difcovered the means of foftening, and not of compleatly diffolving this refin. See Father Charlevoix's Hiftory of St. Domingo. doubtedly doubtedly an exaggeration, and the latter implies a manifeft impoffibility. It really however poffeffes fuch a degree of elaf ticity and fuppleness, as renders it an object equally interefting to the experimental philofopher, and to the artift; who muž naturally wish to avail themselves of its properties, if a method were difcovered of giving it any form that was required. Its chemical properties are not lefs extraordinary; as this intractable fubftance had hitherto refifted every attempt that had been made to reduce it to its original fluid ftate: at least so as that, after it had acquired a new form, by means of a proper mould, it might be dried, and at the fame time recover its for. mer pliability and elafticity. We fhall pals over the fruitless effays made for this purpose by M. Frefneau and others, that we may have room to relate more at large thofe of the prefent Author: premifing only that it had before been found not to be foluble in water; that, though called a refin, it was perfectly indiffoluble likewife in fpirit of wine; and that though it has been diffolved in certain oils; the folution, in whatever manner afterwards treated, remained foft, of a viscous confiftence, and totally incapable of being reduced to a folid and elaftic state. M. Macquer nevertheless fubjected it afresh to the action of various oils, those called drying particularly, and in different combinations; but without effe&t. He entertained hopes that camphire might be made inftrumental in diffolving it; and as that fubftance is the most volatile of all the oily concretes with which we are acquainted (being the only one that will evaporate intirely in a moderate heat, without leaving any refiduum) it feemed that it might eafily be afterwards feparated from the refin. But as the camphire must be melted in order to act upon this substance, and as it can scarce undergo the heat neceffary for this purpose, without fubliming, M. Macquer first liquified the camphire with a fmall quantity of rectified fpirit. In this ftate it really acted upon the refin, and diffolved a part of it; but when the camphire was afterwards feparated from it by evaporation, or other means, the refin which was left was always obferved to have loft its clafticity. Defpairing of fucceeding in the attempt to diffolve this refractory fubftance, by means of oils, the Author applied to it different kinds of falts; the cauftic alcali particularly, and the various acids. He fubjected it likewife to the powerful action of Papin's digeftor, which reduces the hardest bones to jelly, He afterwards entertained fome icemingly well grounded hopes of effecting its diffolution by means of the milky juices of fome of our European plants; of the milk thistle in particular, the lacteous juice of which, after having been dried, refembles in fome refpects the Cayenne refin, and even poffeffes a certain degree of elafticity:-but all his proceffes were equally inefficacious. In fome of them, the refin was not at all affected; and, in others, was altered or deftroyed. After thus exhaufting almoft every probable refource, one menftruumi only remained to be tried; to which the Author had recourfe with regret, on account of its scarcity and dearness, by its means however he at length refolved this very difficult chemical problem. This menftruum is the vitriolic æther, which quickly and eafily diffolves the whole of this anomalous fubftance; forming with it a transparent tincture, and on its evaporation leaving the refin behind, poffeffed of its former confiftence, elafticity, and all its other properties; and of fuch a form as the operator has chofen to give to it, while in its liquid ftate. Great nicety however, we are informed, is requifite in the choice of the æther employed in this procefs. It is abfolutely neceffary to the fuccefs of this experiment, to rectify 8 or 10 pints of the common æther by a gentle heat, and to set apart for this purpose the two first pints that come over. This, by the bye, our Author obferves, is the only æther on which the chemist can depend, who would investigate the qualities, or the proper action of ether, quatenus æther, on other fubftances. The ufes to which this discovery is applicable appear to be various. The folidity, flexibility, and elafticity of the Caquschouc, and its property of not being affected by aqueous, spirituous, faline, oily, or other common folvents, renders it a proper and valuable matter for the conftruction of tubes, catheters, and various other inftruments, in which thefe united properties are wanted. The method by which the Author made Imali tubes of it is fimple and ingenious. He fit prepares a folid cylindrical mould of wax, of the proper fize and fhape; and then dipping a pencil into the ætherial folution of the refin, daubs the mould over with it, till it is covered with a refinous coat of a fufficient thickness. In order that the tube may be smooth and even, this work must be executed with great expedition; as the æther flies off from the wax and leaves the refin upon it, almoft immediately on its application. He then throws the piece into boiling water; by the heat of which the wax is foon melted, and rifes to the furface; leaving the refinous tube compleatly formed behind. The remaining memoirs of this clafs, and volume, shall be the subjects of a fucceeding article. ART. ART. IX. Joannis Frederici Meckel Nova Experimenta et Obfervationes, &c.— New Experiments and Obfervations relating to the Extremities of the Veins and Lymphatic Veffels of the Human Body; and on the Intentions of Nature in their particular Organifation. By John Frederick Meckel. Svo Berlin, 1772. TH HESE experiments and obfervations, which are addreffed to the long and juftly celebrated Morgagni, do not appear to be undeferving the refpectable patronage of that anatomical and medical Neftor of the prefent age: as they prefent fome new and curious circumftances, relating to the ftructure and œconomy of the lymphatic veffels, and veins, in different organs of the human body, which had hitherto escaped the detection of the moft accurate and expert anatomifts. The effay is divided into five fections; from the first of which it appears that the Author's mercurial injections made their way from the fmall lymphatic veffels of the conglobate glands, directly into the branches of the fanguiferous vein of the gland; and this, without any rupture of the veffels, or extravafation of the fluid, attending the experiment. From hence it neceffarily follows that there is an immediate anastomosis or inofculation of the lymphatic veffels with the extremities of the veins belonging to these glands. The fecond fection contains an account of fome eafy and fimple experiments, in which the quickfilver was introduced into the lactiferous ducts of the papilla, in the breafts of two females; and which prove, not only that there is an immediate vascular connection between the minute branches of these ducts, and the lymphatic veins; (an inofculation which had been before detected by our Author's colleague, Walterus) but that there is likewife a fimilar and ftill more evident and open communication between thefe ducts, and the extremities of the red or fanguiferous veins. By means of this peculiar and hitherto undifcovered organifation, the milk is occafionally reconveyed, from the lactiferous tubes, by a direct courfe, into the mafs of blood, from which it had before been fecreted. In the course of thefe experiments the Author difcovered likewise an inofculation of the finalleft branches of the lactiferous ducts with each other. Thefe and the other discoveries and obfervations contained in the following fections are fucceeded by fome phyfiological and pathological remarks; in which the Author inveftigates the intentions of nature in the ftructure of the parts, and points out the medical or curative indications to be derived from the new lights here thrown upon it. As there seems to be nothing peculiar in M. Meckel's manner of conducting the experi 7 ments |