cefs which forms the main fubject of the prefent investigation, much new light was thrown upon the latter. When fulphuric acid, for example, is digested upon turpentine or refin, the oxygen of the former uniting with the hydrogen and carbon of the latter, feverally, leaves the acid in the state of fulphureous acid, and produces water and coal. If the process is carried on gradually, before the coal is obtained, we get fucceffively yellow refin, brown refin, and black refin. Now, Mr Hatchett digested with nitric acid, firft turpentine itself, then these three refins obtained from the treatment of turpentine with fulphuric acid, and lastly, the coal which is formed at the close of the fame procefs. Neither the turpentine, nor the yellow nor the brown refin, gave any of the tanning fubftance; the black refin yielded a confiderable portion of it, and the coal a great abundance. Other fubftances, reduced to coal by the fame procefs, yielded the tanning refiduum with equal facility; as various woods. copal, amber and wax. Nor is the treatment with nitrous acid the only method of obtaining this tanning substance, from coals made in the humid way. For after refins have been long digefted with fulphuric acid, fo as to give coal, if they are then digefted with alcohol, a folution is obtained, which confists in part of the fubftance in queftion. Our author ingeniously conjectures, that fome procefs of this fort takes place naturally in feveral formations of peat; and thus accounts for the complete tanning which is frequently found to go on in thofe moffes where animal bodies have been buried.

The substance resembling tannin, which our author's experiments yielded, was employed with perfect fuccess in tanning kins. This operation he effected with ease, by means of fawduft, pit-coal, wax-candle, part of the fkin itself, and various other materials, not hitherto fufpected of fubferviency to such a process.

The only property in which this artificial fubftance feems at firft fight to differ from tannin, is, that the former is produced by means of nitric acid; whereas, the latter is deftroyed by it. In order to examine the particulars of this diverfity, our author inftituted several experiments. The artificial fubftance was fubjected to repeated diftillations with nitric acid, and found to remain unchanged. The precipitate of gelatine by the artificial fubftance, was washed and dried, and then 'digested in nitric acid, which acted powerfully on it, and formed a dark folation with evolution of nitrous gas. The folution being evaporated to drynefs, and diffolved in water, was found to have the fame action on ifinglafs, acetite of lead, &c. as the fubftance which had not undergone thefe operations. The folutions of this fub

ftance,

tance, are alfo quite indeftructible by the putrefactive process. Nor do they become mouldy like thofe of galls, fumach, &c. But are there no varieties in point of deftructibility among the different forts of natural tannin? Our author thinks that his experiments entitle him to answer this question in the affirmative. For having compared, in this refpect, the folutions obtained from galls, fumach, oak-wood and oak-bark, he found that the laft was much lefs deftructible by treatment with nitrous acid, than the other three, though the artificial product was ftill lefs affected by the acid than any.

The artificial fubftance hitherto confidered, owes its origin to digeflion of nitric acid upon charcoal, whether of animal, vegetable, or mineral bodies. But it appears that a fimilar product may be obtained from the exhibition of this acid to bodies not in a charred or coally state; and that the process of charring only aflits the production of the tanning fubftance, by favouring the feparation of the carbonaceous particles from the other ingredients of the mafs. Our author afcertained this important point by well conducted experiments, firft with indigo, a body known to contain a large portion of carbon. Nitric acid acted violently upon this fubftance; and the application of a gentle heat was employed to evaporate the folution: The refiduum being diffolved in water, was found to contain a large tincture of the tanning fubftance; other bodies, though in a lefs degree, yet fenfibly yield the fame product, by repeated digeftions and diftillations with nitric acid. Thus, common refin, stick lac, balfam of Peru, benzoin, balfam of Tolu, all gave the tanning fubftance by digeftion with nitric acid; and from thefe experiments, and others which he details with a variety of different bodies, our author is induced to think, that there are very few vegetable substances from which a quantity of the tanning compound may not be obtained, by means of the fame acid properly exhibited to them. Many vegetable fubftances yield by decoction, after being roafted, a liquor refembling tannin; but Mr Hatchett found it very dithcult to apply the precife degree of heat which is required to develope whatever taunin they may contain. Even coffee did not yield a precipitate till fome time had elapfed, and then it was foluble in boiling water; but what he calls a coffee prepared from the chicoric root,' gave a precipitate, foluble indeed ia boiling water, but reproduced when the water cooled. All thefe decoctions, when treated with nitric acid, yielded a tanning fabitance fimilar to that obtained in the former courfe of experi

ments.

From the whole it appears, that the artificial fubftance resembling tansin may be produced in three feveral ways, by digeftion

of

of nitric acid on any carbonaceous fubftance, animal, vegetable, or mineral; by diftilling the fame acid from indigo, refins, and various other fubftances; by treating refin, camphor, &c. with alcohol, after they have previously been digefted with fulphuric acid. Of these three methods, the firft is that which produces the substance most easily, and in the greatest abundance, a hundred grains of vegetable charcoal yielding about 116 of the fubftance.

The properties of the body in queftion are juftly deemed by Mr Hatchett to be very fingular. Not only its entire refemblance to tannin, except in its relation to nitric acid, but feveral other particulars in its habitudes, merit our notice. If a portion of this substance, procured from pure vegetable charcoal, be expofed dry to the action of heat, it emits an odour refembling that of burnt feathers, horn, and other animal bodies. If it is expofed in a retort to the diftilling procefs, a red heat fends off the fuperfluous moisture, and nitrous fumes alfo rife into the retort; when the heat is pushed higher, a white cloud fuddenly fills the apparatus, faline matter is found on the retort, and gas efcapes, almost with explosive force. This is evidently caused by the evolution of ammoniacal gas, which unites with the nitrous fumes, and forms, as ufual, a cloud of nitrate of ammonia. Hence the artificial fubftance confifts of hydrogen, oxygen, and nitrogen, with a base of carbon; and, as our author had taken every precaution to exclude impurities from the charcoal employed in his experiments for obtaining the fubftance upon which he operated, he was led to infer, with much confidence, as a corollary from the experiments laft mentioned, that hydrogen exists in charcoal, but further confideration, he admits, had induced him to fufpend this judgment; for he has always found the dilution of the nitric acid employed in his experiments favour in an eminent degree the formation of the tanning fubftance; and this would feem to indicate, that the hydrogen which goes to the compofition of that body owes its origin to the water.

The different varieties of this fubftance exhibit fome little diverfity of properties. That which is obtained from carbonaceous bodies, by digeftion with nitrous acid, is much more abundantly produced than either of the other fpecies; the precipitates which it yields with gelatine are of a deep brown colour, while the colour of the fecond variety is bright yellow; both these varieties are more powerful in their action upon fkin than the third, which, moreover, feems not to contain any nitrogen; at least, fuch is our author's inference from confidering the manner of its formation; and by this deficiency in its compofition he thinks

its

its inferior ftrength may be explained. But upon these matters he promises a further communication.

We have little to add upon the fubitance, as we have now given it, of thefe fpeculations. Their importance can as little be queftioned as their general accuracy and folidity. We are difpofed to view the difcovery of Mr Hatchett as one of the most valuable that have been for many years prefented to the chemical world, whether we view it as introducing us to the knowledge of a new body, or as thewing how, in all probability, a known fubftance is elaborated by Nature in the procefs of vegetation. By profecut ing thefe interefting inquiries, we are fanguine in our hopes that much light will be thrown upon the physiology of plants; and entertain very little doubt that Mr Hatchett is on the eve of an improvement, perhaps the most valuable that has been made in the useful arts in modern times.

ART. VI. Journal des Mines, publié par l'Agence des Mines de la République. No. I. 8vo. Paris. An 3.

THE plan of this periodical publication, the mafs of important and accurate information which it contains, and the laudable zeal for the prosecution of scientific and practical mineralogy which we trust it will excite in our own country, have induced us to give a fhort account of it from the commencement of the series. It cannot be expected, however, that we should dwell on many of the articles feparately. Thofe, for example, which require the illuftration of plates, or are already too compreffed, or are copied from other works, or which, from their nature, are not fufceptible of abridgement or analyfis, we fhall not regard as belonging to our cognizance. Thus we are compelled to pafs in filence various defcriptions of machinery; fome excellent cryftallographical papers by Hauy, &c.; delineations of fubterraneous workings; fections of local stratification; the condenfed forms of several valuable memoirs; interefting analytical refults obtained by Klaproth, Vauquelin and others, and which are now generally known through other channels; various extracts and tranflations from the transactions of learned bodies, and from foreign or domestic publications; and fuch communications as are of a strictly technical or tabular aspect.

As our intention is rather to give our readers an idea of the plan on which the work proceeds, and to invite those whom it may concern to perufe its contents, than to fcrutinize its merits with critical minuteness, we shall even abstain from the mode of difquifition in reporting fuch articles as have chiefly attracted our

attention,

attention, and fhall, in most cases, be contented with intimating their object and principal refults.

In the most stormy and eventful period of the French revolution, the Committee of Public Safety inftituted a Board of Mines, confifting of three members. Subordinate to them were eight inspectors, twelve engineers, and forty pupils. The annual falary of the infpectors was fixed at 6000 livres, of the engineers at 3000, and of the pupils at 1500, not including travelling expences. The infpectors and engineers were propofed by the members of the Board, and approved by the Committee of Safety, and the nomination of the pupils was determined by a public comparative trial. Infpectors, engineers, and pupils were enjoined to travel eight months in the year, and to refide the remaining four at Paris. Two pupils were affigned by lot to each infpector and engineer, to accompany them on their profeffional million. The French territory, in regard to the mining department, was divided into eight circles. To the annual survey of each circle one infpector and one engineer were appointed by lot; and each of thefe officers examined the fame circle for two fucceffive years. The four fupernumerary engineers were deftined to replace fuch of their colleagues as happened to be indisposed, or employed by government in other functions.

The principal duties required of the infpectors and engineers in their mineralogical tours, were the vifitation of mines, the communication of ufeful advice to the directors of the works, and infpection of the machinery, &c. with regard to folidity and the fafety of the workmen. They were, moreover, inftructed to vifit founderies, and all establishments connected with the mining art, and to favour the directors of fuch establishments with fuitable hints and fuggeftions. They were particularly defired to inftruct their pupils, and to give them practical leffons on all matters connected with their profeffion. Befides collecting fpecimens of all the fofil fubftances contained in the circle, and forwarding the collection, with proper catalogues, to the Board at Paris, they were requested to sketch plans of their difcoveries; to detail the practical operations which obtain in founderies and manufactories connected with mining; to make drawings of machines, furnaces, and of the modes of working under ground; to keep a regifter of their travelling ftations, and of the fubftances which they found, and the experiments which they made at each; and to tranfmit their memoirs, journals, and drawings, once in ten days, to the Board. When they discovered any foffil fubftance which could be turned to good account, they were to invite the proprietors of the ground, or, in their default, the nearest inhabitants, to work it, and to afford them every encouragement, af

Eftances