tle, more penetrating, moveable, and light. If the quantity of heat is accumulated till it becomes equal to 100°, it is diffolved into elastic vapours; fome of which are already generated before the degree of heat is equal to 100°; but fo much the lefs, the lefs the quantity of heat exceeds the abovementioned degree of faturation.In the very moment they are separated from the mafs it cools; for all evaporation generates cold. Does this cold arife because the increased volume requires more to its faturation, and can in confequence of its effect, fix more heat than before? Or is the heat (which was united to the water and was increased to a certain degree) now enabled to confolidate itself clofer and in greater abundance, and to carry off in confequence that part of the water which is nearest at hand? -This is what experiments have taught us of the compofition of water; plainly demonftrating that it by no means ought to be confidered as a fimple fubftance.

I have before mentioned fomething about air, and proved, that the fubftance commonly called by that name, is by no means a fimple and homogeneous body. I need not likewise be prolix on this, and the thus called fourth element or fire; fince these two are the objects of the following performance;-whofe author, Mr. Scheele, has great merit in chemistry by several important difcoveries; all his inquiries fhewing not only his reflection and reafoning, but also a peculiar fkill and perfeverance in inveftigating truth, both by analyfis and by fynthesis. Newton's difcovery to

nearer

divide light (the infinitely fubtle light) into colours, has opened the way to many very curious myfteries of nature, though it was no more than a mechanical divifion. Mr Scheele discloses a more fubtle, becaufe a chemical analyfis; which inffructs us not only about light, but alfo about fire, whofe explication has hitherto been the crux philofophiæ. I have, with feveral alterations, repeated his principal experiments on which he grounds his doctrine on this fubject, and found them perfectly accurate. Though in fome leis material circumstances a confirmation might become neceffary; it does however no injury to the main fubject; which is grounded on feveral correfponding experiments. Heat, fire, and light, are, in regard to the elementary principle, the fame with good air and phlogifton; but their proportion, and perhaps the manner of their compofition, caufe the great difference. Phlogiston feems to be a real elementary principle, which enters the chief part of fubftances, and adheres to them moft obftinately. There are feveral means to separate it more or lefs perfectly: of thofe known fubftances, good air is most active; for which reafon, I put its fign at the very top of the column of phlogifton in my new table of attractions; what it cannot do fuddenly, is however done gradually by the intervention of favourable circumstances.

How interefting the more refined chemistry is, will not be neceffary to prove more circumftantially on the prefent occafion. It requires a great deal of prejudice, or the greatest ignorance, to treat

it with contempt under the fpecious pretence of unneceffary refinement and fubtleties. Earth, water, air, heat, light, and many more fuch fubtle fubftances are every where to be met with; and as long as their properties, remain unknown, the effects both of nature and art, must remain involved in the moft perfect ob.

fcurity. In chemistry, there are none of the veritates otiofe; the leaft phænomenon, when examined in all its caufes, is always connected with others of the greatest importance; in fuch a manner, that every thing is fhewn connected in the great economy of nature.

USEFUL

The diforder in question has been, i believe, more confidered from its eff. &ts, its remote, and concurrent caufes than from its immediate caufe: hence we may account for the inefficacy of the various attempts to cure it.

The pen of writers has done little more in the bloody flux, than record the times and places when and where it proved most fatal; the appearance it put on; its fympt ms; its devaftation ; variety of modes of treatment that had no certain fuccefs: now and then a remarkable cafe, and the phenomena difcovered on diffecting the dead.

The great author above mentioned, following nature as an unerring guide, never stopped at effects, but proceeded on to the caufes of diseases; and affifted the means employed by nature to remove them, or fubftitute a safer and better me:hod;-to which principle the world is indebted for that ineftimable work that can only perifh with it; a work founded in nature, on a bafis applicable to all climes; that stands as the Palladium of phyfic against the fuperftitious errors of the middle ages and the ingenious chimeras of later times;-he difcovered the dyfentery to be, " fever of the jeason, or of it. own kind, turned inwards upon the inteftines ;" and yet his fucceffors have made but little father use of this excellent aphorifm, than quoting it, as their rules laid down for treating the disease sufficiently prove.

a

In the courfe of twelve years experience in this ifland, and from every account I have been able to procure from all parts of the Weft-Indies, I have invariably found the truth of Sydenham's opinion; and have remarked that as the flux diftinguishes, by the num

ber

ber of ftools, the quantity, fo it does the state of the fever of the feafon, when it prevails, or of the fubject difeafed; the ftools being more frequent at thofe hours when fevers are in their exacerbation, and the reverse when in their remiffion; befides, their alternate fucceffion is frequently obferved; nor can it be doubted that this fever, like most o hers, is caused by obftructed perspiration; not confined to cold, hot, wet, or dry feasons, particular food, water, liquors, or fruit; but chiefly depending on fudden tranfitions, and fuch other caufes, as expofe people to have this difcharge haftily stopped.

I know that writers lay great ftrefs on exciting, and internal pre-difpofing caufes; heat and moisture; putrid ferments; infection, &c. &c.-but, upon a ftri&t examination, we fhall find, that there has been too much attention employed on thefe imaginary circumstances, whilft the immediae caufe, or primum mobile remains unnoticed. It is not to be doubted, that a conjunct caufe is neceffary, otherwife obftructed perfpiration, the parent of fo many, would always produce the fame disease.

The fkin being the great outlet for infenfible perfpiration, which is faid by Sanctorius to amount, in the temperate clime of Italy, to five-eighths of what is taken into the body, we cannot be furprised at the violent efforts nature immediately makes, on the fudden fuppreflion of a habit of fuch extent and if we attend to the ftools of fome patients, after the common contents of the bowels are difcharged, before the

blood-veffels are broken, and at intervals when there is no mixture of blood or mucus, we shall find, they are nothing but a ferous, acrid fluid.

As I have conftantly practifed in the opinion, that a flux is a certain fever of the intestines, and that this fever is caufed by the obftructed perspiration being thrown there-fo I have ever found it relieved, by turning back that dif charge to its natural channel; nor have I often found difficulty in removing it fpeedily, when taken in the beginning.

The common and fatal practice, of attacking the disorder in the bowels, with opiates and aftringents, is but aggravating the effect, whilft the caufe is entirely neglected.

Among the multitude of formula propofed for the flux, we find Snake-root, Dover's powder, and other diaphoretic medicines; but exhibited in fuch a manner, that they must often have produced more harm than good:- however, it plainly demonftrates that the fkin has not been really looked to for relief,-much less has the procefs of fweating been confidered as the only one to be relied on.

Sir John Pringle recommends ipecacuanha in fmall dofes, united with philonium and opium—Dr. Huck, and many others, a course of ipecacuanha in stages of the difeafe when the inflammatory fymptoms are over; the good effects are attributed to aftringency;— but, with the greatest deference poffible to fuch authority, I believe ipecacuanha increases the tendency of the humours to the skin, and therein confifts its ufe in fluxes. I apprehend that no aftrin

gent,

The activity of emetic tartar, makes the direction of it difficult : it is in many refpects a dangerous medicine in hot climates, the nervous fyftem being fo irritable

Monfieur De Senac gave emetic tartar in fmall dofes; but he exprefly fays, he gave it as a laxative, to keep up a free paffage from the ftomach to the rectum. It is a common practice to give the glass, and other preparations of antimony, in cafual dofes, and uncertain periods; but the operation is always intended for the firft paffages. In this practice, though the prime via are fo neceffary to be cleanfed, I attribute the principal fuccefs to the effects which antimonials produce, in opening the obftructed capillaries, and preventing a reflux of humours to the bowels: for often in fluxes, when, from careleffness and cold, antimonials have had their whole force, and action turned upon the bowels, they have increased the determination of the fluids there, and brought on fudden death; and in fevers alfo, the ftomach is fometimes deftroyed by them. When emetic tartar is injudiciously given to young, irritable, plethoric people, in the beginning of a fever, and previous to proper evacuations, inftead of exciting a diaphorefis, a fpafm is produced in the ftomach, inceffant vomiting, inflammation, the veffels of the thorax and head are ftifled with blood, and the patient vomits away his life.

Such preparations of antimony as, from the effects, I fhould fup. pofe James's powder to be, that have its phlogiston mitigated, and the reguline part capable of action, from acidity, are beft in fevers, being moft certainly fudorific; their operation on the ftomach or bowels confiderably depends on the state of the humours contained there, and they principally become active when nature requires it.

Dr. Cullen objects, that the dofes of these preparations of antimony, cannot be fo well afcertained, as its folution by the vegetable acid; for which reafon he prefers the emetic tartar for use.

It must be admitted, that emetic tartar is a certain vomit, and when given for that purpose the dofe is eafily afcertained ;-but as it acts immediately on the ftomach, it is frequently impoffible to produce any other effect by it, dofe it how you will.-This learned phyfician has greatly contributed to the general use of emetic tartar; the abufe of it has arifen from our respect to his character.

When we obferve with what circumfpection and prudence the most enlightened and scientific in

troduce