the medical fcience without the application of a chemical analyfis? The mufes were not without reafon thought to be fifters; and they are a moft excellent emblem of that harmonic union, by which all the fciences mutually affift one another; and without which they never can attain any degree of perfection.

Next to health, there is nothing more preffing and neceffary than common food. In order to convince us of the utility produced by chemistry in regard to the neceffaries of life, we fhall only take a view of agriculture, that most antient and noble occupation. If we confult Columellä, and many of the most antient writers on hufbandry, we find to our humiliation and fhame, that they were as well inftructed as us, if not better; though in later times fo much pains have been taken, fo many encouragements have been given, and fo many rewards have been diftributed. This ought to be confidered in the following manner. The great Lord of nature has fo bountifully taken care of us, that corn grows without ány great care and knowledge. The improvements which this art in general is capable of from experience and collected experiments, are likewife foon enough acquired; and in this ftate it remains till the science of nature throws a new light upon it. They are two very diftin&t things, to raife corn on a certain piece of ground, and to raife as much corn as will poffibly grow there:

The last defideratum is not always obtained by ploughing, ditching and manuring; for befides thefe mechanical operations,

there are two things more requir ed: fuch a mixture as will afford to the vegetables not only proper nourishment; but alfo fuch a one as keeps humidity as long as the ufual drought makes it requifite; for nothing grows, even in the most exquifite foil, without water. The best compound, therefore, ought to be adapted to the nature of the foil, the expofure, the climate, and the common temperature of the weather; as I have proved more at large in another place. In the mean time it will be eafly found, that chemiftry is of the fame importance to agriculture and all the more particular branches of rural œconomy, that aftronomy is to navigation.

The arts and mechanical trades, are occupied with the melioration of raw materials. One part of them, from beginning to end, is a feries of chemical operations; others are more mechanical ; however there is hardly one of them which contains not one cr more problems whofe more perfect folution depends upon chemiftry only. What a number of years must have elapfed before they arrived by chance only, or by unpremeditated experiments, to their prefent perfection; or before they learned to avoid all occurring inconveniences. A perfect knowledge of the raw mate. rials, often furnishes the best inftructions, in a direct way. And it has been hitherto a great misfortune, that the practical part of the arts has been kept very fe cret: but fince the French Acade my of Sciences has begun to remove this obftacle, we have the moft certain expectations of their G 2

quick

quick and amazing progrefs, by the affiftance of the fcience of nature. Without the knowledge of the true causes and their connections, it is impoffible either to obviate or to remove all the obftacles arifing from chance or accidental circumftances.

lows, that chemiftry fhould not be able to difclofe to our eyes many a fcene of wonders. Could we only discover with certainty, the elementary principles of bodies (principia proxima) together with their connections and proportions, chemistry would be able to do great things.

From what has been faid in a few words, it must evidently appear, that chemistry in a peculiar manner, throws a great light on all mechanical trades, concerned with corporeal fubftances.-However the property of the fubject itfelf feems to prefcribe limits to this fcience. The quality of our fenfes, even when affifted and improved by art, will not let us penetrate farther than to a certain point. The fubtlenefs of our intruments is infufficient, and the beft become at laft ufelefs. All thefe difficulties are ftill more increased, from the most subtle particles which cannot well fall under the examination of our bare fenfes, having not only the greateft adhesion and confequently exercifing the greatest refiftance to the attempts of dividing them, but also affording the most effectual and active means for this end. How imperfect therefore, must be our moft perfect knowledge of the mysteries of nature?

From the most early periods, certain fubftances were thought to be fo fimple, that art gave up all hopes of analyfing them any further, and these were therefore confidered as the ftamina prima. Such are more efpecially the four Ariftotelic elements, earth, water, air, and fire: to discover the compofition of which is the business of higher and more refined chemiftry. Let us therefore examine, whether all hopes are entirely loft of difcovering any thing here.Earth is the fixed principle, which remains after the fire has exerted its deftroying power against a body, and which is not foluble in water in the common way. This is the coarseft of all the four common elements, and makes but a fmall part of the bodies. Whatever analyfis has hitherto been able to eftablish with certainty, may be reduced to this; that earth (which after all proves to be of different fubftances) is by no means the fame matter, nor homogeneous, but a compound of feveral; and is found to be more or lefs of a faline nature, at leaft it is fo on the surface of our globe, in its moft pure ftate. There have been found fix different fpecies; having all quite different properties, and which hitherto have neither been decompounded into more fimple, nor been changed into another: viz. 1. The earth

This is all perfectly right; and the pretenfion is fupremely filly, to be able at a future period to inveftigate the firft powers, which the Creator has established at the creation and for the prefervation of the material world. Such a fcience is too abftrufe, and reaches beyond our attainment; it is referved for the power of the Creator, and not for that of a creature. But it by no means fol

of the ponderous Spar; 2. calcareous earth; 3. magnefia; 4. clay; 5. filiceous earth; and 6. earth of gems. I have in another place mentioned the characteristics of them. Whether thefe, which till a further investigation may be called primitive earths, are really different, or only varieties of the fame, I cannot tell; the laft opinion feems to be the most fimple. I have however before obferved the dangerous error of limiting the order of nature to our confined ideas. The conclufion ought not to be formed before the premises are ascertained by experiments. Patience and affiduous application may perhaps in future times make difcoveries; fince we have at least fome confiderable number of notions about their properties, by which a great deal is already gained. But fince the acid of йuor and water, meeting one another in the form of vapours, coagulate into filiceous earth; and acid of arfenic with phlogifton coagulate into folid white arfenic; there is fome indication that terreous fubftances, as well as metallic calxes, may be confidered in their firft principles as acids; which in the first cafe are become fixed by water, and in the laft by phlogiston. Thus much at least is certain, that nature has indiçated itself to be poffeffed of an abundance and variety of acids; and that it particularly employs them in its various operations.

means prove that which in the beginning had been fufpected of them. It is generally known, that heat caufes peculiar changes in water. The particles of water ftrongly attract the particles of heat; and after they have been charged with, or enveloped by a certain quantity of them, this compounded matter becomes fo eafily moveable, that its furface endeavours conftantly to form a horizontal line; it has a great fimilarity with a fubtle earth melted by fire. If you diminish the heat, by which operation the furface of the particles either come in contact and by their friction hinder this reciprocal motion, or the elasticity and power of repulfion is fufficiently diminished by the feparation of one of these elementary principles, then the mafs becomes indurated and ice is formed. It is not yet determined, which of these causes is here prevalent. If ice is to be melted, a quantity of the employed heat is loft, amounting to very near 72° of our thermometers, and forms a kind of faturation; fo that its effect is concealed by its union with the ice, almoft in the fame manner as if an acid were hindered from exercifing its characteristic properties by a faturation with alkalies. 'The fame takes place with quicklime: it contains heat, which is inactive till a ftronger elective attraction fets free and expels it. By the abforption of 72° of heat, ice is made fluid; that which it receives beyond it is fuperfluous; which may be eafily obferved, in the fame manner as in adding an acid to a neutral falt: the water expands, grows warmer, more fub

Water is ftill more fubtle, and with more difficulty decompounded.-Upon more accurate examination we find, that the experiments according to which it was imagined, that water could be changed into earth, do by no

G ́3

tle,

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 mo. ment they are separated from the mafs it cools; for all evaporation generates cold. Does this cold arise 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 likewife be prolix on this, and the thus called fourth element or fire; fince thefe two are the objects of the following performance; whofe author, Mr. Scheele, has great merit in chemistry by feveral important difcoveries; all his inquiries fhewing not only his reflection and reasoning, but also a peculiar fkill and perfeverance in inveftigating truth, both by analysis and by fynthesis. Newton's difcovery to

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 difclofes a more fubtle, becaufe a chemical analyfis; which inftructs us not only about light, but also about fire, whofe explication has hitherto been the crux philofophia. 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 lefs material circumstances a nearer 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 phlogiston; 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 feparate 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 circumftances.

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 unneceflary 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, muft 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 greateft importance; in fuch a manner, that every thing is fhewn connected in the great economy of nature.

G4

USEFUL