itself entirely from the cavity in which it terminates, but its action as a capillary tube will not tend in the finallest degree to propel the lymph into the veins.

It is moft probable that the joint of the lymphatic, next to the cavity, having abforbed a fufficient quantity of lymph to fill it, is ftimulated to contract and propel the fluid into the next joint, and fo on to the thoracic duct, or vein, in which it terminates; and having emptied itself, and being relaxed, it fills itfelf again from the cavity, and fo continues to act: for there is apparently no other power in the body capable of producing a regular flow of the lymph through the lymphatics into the blood veffels.

For in a living animal where the veins are contracting, and preffing the blood, if one end of a capillary tube terminate in a vein, and the other in a cavity; and if there be no action in that tube, excepting that which arifes from its being a capillary one, or from the motion of the blood in the vein if there be any motion in that tube after it is full, it will always be from the vein into the cavity, and never from the cavity into the vein, let the tube be of any fize or fhape whatever.

Further; the alternate preffure of the lymphatics arifing from the alternate contractions and relaxations of the bloodveffels, or muscles, is not fufficiently powerful, univerfal, or equal, to produce a regular flow of the lymph through the lymphatics into the blood-veffels.

Neither does the cellular membrane and cavities force the lymph into the lymphatics, and through them into the veins.

The extravafation of fluids from the blood-veffels into the cellular membrane and cavities, and their re-abforption, generally take place in the above manner.

Sometimes the coagulable lymph is thrown out by the ex

halants.

When the coagulable lymph is thrown out, it most commonly coagulates.

If it coagulate, it cannot be taken up by the lymphatics, till it be rediffolved.

In many cafes it rediffolves, and is abforbed much fooner than it can be rendered foluble in water, by putrefaction when out of the body. At other times it continues in the cavity for many years.

The red part of the blood is alfo fometimes thrown out by the exhalants. In this cafe, its particles are broke down probably by the firft ftage of putrefaction, and it is afterwards reabforbed.

The fame things may happen, if the red particles and coagulable lymph are extravafated in confequence of the rupture of a blood-veffel.

In particular parts, as in the corpora cavernofa penis, the extravafation and abforption is probably performed in a different manner, and by different veffels.

All abforbent veffels must have a power of propelling the Aluids into the blood-veffels, fufficient to overcome the force of their contraction, by which they endeavour to propel the blood out of any opening.'

Dr Fordyce appears to poffefs a confiderable ftock of phyfiological knowledge, and, at the fame time, to have a happy fyftematic turn.

ART. IX. An Efay towards a Syftem of Mineralogy: By Axel Frederic Cronstedt. Tranflated from the Original Swedish, with Notes, by Gustav von Engeftrom. To which is added, A Treatise on the Pocket-Laboratory, containing, An easy Method, ufed by the Author, for trying Mineral Bodics, written by the Tranflator. The whole revifed and corrected, with fome additional Notes, by Emanuel Mendes Da Cofta. 8vo. Pr. 4s. Dilly. 1770.

IN

N this Effay, the great variety of fubjects which constitute the mineral kingdom, are divided into four claffes, viz. 1. Earths. 2. Inflammables. 3. Salts. 4. Metals.

Thefe claffes are divided into orders, and these orders are again fubdivided into varieties.

The four general claffes are thus defigned by our Author. 1. Earth, or thofe fubftances which are not ductile, are mostly indiffoluble in water or oil, and preferve their conftitution in a ftrong heat.

2. Inflammables, which can be diffolved in oils, but not in water, and are inflammable.

3. Salts: thefe diffolve in water, and give it a tafte; and when the quantity of water required to keep them in diffolution is evaporated, they concrete again into folid and angular bo

dies.

4. Metals are the heaviest of all bodies hitherto known; fome of which are malleable, and fome can be decompounded; nevertheless, in a melting heat they can again be recovered, or brought to their former ftate, by adding to them the phlogiston they loft during their decompofition.'

The earths are divided into nine orders, viz. 1. Calcareous: 2. Siliceous: 3. Garnet kind: 4. Argillaceous: 5. Micaceous: 6. Fluores: 7. Afbeftus-kind: 8. Zeolites: 9. Manganese. The following is our Author's defcription of the Argillaceous, or fourth order of earths.

The principal character whereby thefe may be diftinguished from other earths, is, that they harden in the fire, and are com

pounded

pounded of very minute particles, by which they receive a dead or dull appearance when broken.

Moreover, there are fome of this order which grow foft in water, and, when only moistened, become ductile and tenacious these are commonly called clays. Some crack in the water, after having imbibed a fufficient quantity of it, but do not grow fofter in it, and are therefore in the first degree of induration: fome imbibe the water, but do not crack or fall to pieces; these are yet more indurated: and finally, fome there are, in which the water has no ingrefs at all. Thus, by following the fucceffive gradation of induration of a fubftance, which throughout all thefe circumftances is eafily difcovered to be the fame, one may with great reafon conclude, that the hardness of the jafper may perhaps be the laft degree of hardnefs, and that this ftone confequently confifts of an argillaceous fubftance, that already poffefles a quality which the other clays cannot acquire but in the fire; having, befides, the fame effec as the boles when melted in the fire together with calcareous or other earths.'

The fubdivifions under this order, are, 1. Porcelane clay. 2. Stone marrow, Lithomarga: Keffekil of the Tartars. 3. Bole, 4. Tripoli. 5. Common clay, or brick-clay.

After pointing out the characters of thefe fubdivifions, and of the varieties likewife which occur under thefe fubdivifions; he concludes his account of this order with

Obfervations on clays in general.

Those who have taken upon themfelves to examine the mineral bodies according to the principles upon which this fyftem is built, will readily, I hope, excufe thofe faults which may have been committed in claffing the clays; because they muft well know, not only how difficult it is to procure a number of different varieties of this order in their natural ftate, which have not been previously washed or prepared for ufe, as the fealed earths, &c. but also that it is no eafy matter diftinctly to defcribe fome little circumstances that occur to the eye, both in their natural state, and during the experiments. Befides, they cannot but remember, that the progreffional degrees, both of hardness, and of the quantity of mixed heterogeneous bodies,. efpecially iron, produce a number of imperceptible differences between them, in regard to colour and effects; fo that they cannot with due precifion be feparated and divided into their true genera, fpecies, and varieties, before fome more evident differences between them may, by repeated experiments, and perhaps by proceffes yet unknown, be difcovered. In examining the clays, one ought carefully to obferve the different degrees of fire due to each kind; for without this knowledge they can ne

ver

ver be employed to any real ufe in common life. Next to this, there is another point equally neceffary to be taken notice of, that is, the manner of working the clays, which is often different in different kinds, and which, not less than the different degrees of fire, is productive of different effects; and therefore, if both thefe circumftances are not at the fame time exactly defcribed, it is as wrong to affert with fome authors, that a refractory clay does never crack in the fire, as it is deceiving to pretend that the fame clay does never imbibe the water, when it has been baked. Hence comes that great difference in regard both to appearances and qualities, between a tobacco-pipe, which is very little baked, and a jar from Waldenburg, between a common brick and the other fort called a water clinkert.

The ufe of clays, in common life, is more extensive than I have been able to inform myfelf of; for which reafon I will only mention fome particulars relating to it.

The porcelane clay is employed to make veffels which have that quality already mentioned. I make no doubt but it enters into the compofition for making the fine porcelane ware at fome places; at least veffels are prepared from it of the fame goodness in every refpect: and there are likewife fome varieties of this clay, which become quite white in the fire, a quality which is efteemed the most valuable in the fine China ware.

The indurated porcelane clay cannot be eafily heated without cracking, and is therefore of no great fervice, if hardened in the fire alone, and in its natural ftate: though this circumftance is of lefs inconveniency, than when it has original cracks, or is mixed with heterogeneous fubftances. The fteatites is found purer and more folid in China than in any place in Europe. The natural faults of the European ones may, however, be altered by adding fome fat fubftance to it, when it is to be burnt; by which means it becomes black or brown; and this method is faid to be used at Bareith. The coarfe porcelane-like earth, which goes by the name of French clay, is ufed at the glasshoufes, fteel-furnaces, and other works of the fame nature, for the fame reasons, as it is the principal ingredient in the making of crucibles, retorts, &c.

The boles have almoft loft their value as medicines, and are employed to make bricks, potters-ware, and pig iron.

The tripoli is an indifpenfible article for the polishing of metals, and fome forts of ftones; it is likewife on certain occafions preferred for making moulds to caft metals in.

The common clay is of the greatest benefit in agriculture, except however the white clay and the fermenting clay, which varieties we know not yet how to apply to any ufe. By virtue of its coherency, this clay retains humidity, on which perhaps its chief benefit to vegetables depends, its other effects being oc

cafional,

cafional, owing either to nature or art; unless the clay has formerly been a mould or humus ater, in which cafe it is juft, that part of it should enter again into the formation of the new vegetables. The clay ufed in the refining of fugar, wants no other quality than that it may not dry too foon. But that fpecies which is to be employed in fulling, muft, if we were to judge à priori, befides the finenefs of its particles, be of a dry nature, or fuch as attracts oils; though this quality may perhaps not be found in all thofe clays which are now employed in that bufinefs.'

ers

As a further fpecimen of this work, we fhall give our Read

THE SEVENTH ORDER.

The Afbeftus kind, Afbeftina.

Thefe are only yet difcovered in an indurated state: their characters are as follow.

1. When pure, they are very refractory in the fire.

2. In large pieces they are flexible.

3. They have dull or uneven furfaces.

4. In the fire they become more brittle.

5. They do not strike fire with the steel.

6. They are not attacked by acids.

7. They are easily brought into fufion by borax.

In this order are included both thofe varieties which by foffilogifts have been mentioned under the names of Amianti and Afbeli, and have often been confounded together.

SEC T. CIII.

1. Afbeftus, which is compounded of foft and thin membranes, Afbeftus membranaceus; Amiantus l'allerii.

A. Of parallel membranes, Afbeflus membranis conflans parallelis: Corium, five Caro Montana, mountain-leather.

Yellowish brown, from Storrginningen, at Dannemora, in the province of Upland.

This melts pretty cafily in the fire to a black flag, or glass.

B. Of twisted foft membranes, Asbestus membranus conftans contortis: Suber montanum, Mountain-cork.

1. Pure.

a. White, from Salberg in Weftmanland. 2. Martial.

sa. Yellow