How does this property of matter operate?

It operates at sensible and at insensible distances.
What instances are there of the former kind of repulsion?

The only kinds of repulsion that can be exhibited to the senses, are those of electricity*, and magnetism+; but it is insensible repulsion with which chymists are more particularly concerned.

What instances have you of this latter kind, or of insensible repulsion ? The only example that we are acquainted with is the repulsion of the particles of calorict amongst themselves; which repulsion would constantly tend to infinite separation, were it not for a chymical union, which, by an irrevocable law of nature, they form with the first surrounding body. For by that law it seems the particles of caloric cannot exist in an isolated state.

How does this repulsive force operate upon other bodies?

It diminishes the cohesion of the integrant particles of all heatad bodies, in consequence of the particles of caloric repelling each other; so that chymical unions, as well as chymical decomposi tions, are wonderfully facilitated by this species of repulsion§.

• If two cork balls be suspended from a body with silk threads so as to touch each other, and we charge that body with electricity, the cork balls will separate immediately. The balls of course repel each other.

† When we present the north pole of a manet A to the same pole of another magnet B, suspended on a pivot, and at liberty to move, the magnet B recedes as the other approaches; and by following it with A at a proper distance, it may be made to turn round on its pivot with considerable velocity. There is then a repulsion between the two magnets➡a repulsion which increases with the power of the magnets; and this power has been made so great, by a proper combination of magnets, that all the force of a strong man is insufficient to make the two north poles touch each other.

It is now generally imagined that what is called insensible repulsion is owing to the presence of caloric. It is well known that the elasticity of air and all other gaseous bodies is increased by heat; that is, that the repulsion between the particles of air, the distance remaining the same, increases with the temperature, so that at last it becomes so great as to overcome every obsta cle which can be opposed to it. This subject is fully treated by Dr. Thomson, to whom I refer the reader.

It is evident, that whatever diminishes the cohesion which exists between the particles of any body, must tend to facilitate their chymical union with the particles of other bodies. One reason why some bodies require a high temperature to cause them to combine, is, that at a low temperature the attrac tion of cohesion is in them superior to that of affinity; accordingly it becomes necessary to weaken that attraction by caloric, till it becomes inferior to that of affinity. In like manner bodies combine more easily when held in solution by water, or when they have previously been reduced to a fine powder, as these operations diminish the cohesion which exists among the primitive or integrant particles. Sulphuric acid has no action upon a lump of Auate of lime; but if that earthy salt be reduced to powder, a violent action will ensue on the addition of the sulphuric acid, and the fluate of lime will be decomposed.

Will you endeavour to explain this action of caloric with more pres

cision?

As chymical affinity takes place only, between the ultimate molecules of bodies, while the attraction of cohesion remains superior to that of affinity, no other union can take place; but whenever caloric has sufficiently diminished this attraction in any substance, the particles are then at liberty to form new combinations, by their union with the particles of other bodies*.

Is the addition of caloric always necessary to promote chymical affinity?

In order for the attraction of composition to take place between two bodies, it is generally necessary either that one of the substances should be in a state of fluidity, or that heat should be applied; so that caloric acts an important part either sensibly or insensibly in all cases of chymical affinity.

Does chymical affinity operate in consequence of the universal law of

attraction?

We have reason to believe that every new compound is produced by virtue of the attraction to which all matter is subject, and which is equally operative on the most minute atom, as on a planetary systemf.

How do you imagine that the same force which operates upon the

The formation of the red oxide of mercury will exemplify the above chymical axiom. If mercury be submitted to a heat little superior to that of boiling water, no new combination will be formed, but the metal will remain unaltered. If the heat be increased to 600°, or thereabouts, the attraction of cohesion of the mercury will be broken; its particles will unite with the oxygen of the surrounding atmosphere; and a new substance, red oxide of mercury, will be produced. If this new substance be again submitted to the operation of caloric, and the heat be raised to 1000°, the combination will again be broken, and new affinities will take place. The affinity of oxygen for calorie will now be greater than that of oxygen for mercury; the oxygen will quit the mercury, unite with the caloric, and be expelled as oxygen gas: thus the mercury will consequently once more appear in its metallic state.

Red lead is formed by long exposure of metallic lead to atmospheric air in a high temperature; but by a great increase of temperature, it is made to give out its oxygen in sufficient abundance to be collected in appropriate receivers in the form of oxygen gas, and the metal becomes revived.

†The attraction of the particles of bodies for each other is exemplified by small quantities of water, or other fluids, which, when dropped upon a flat surface, form themselves into spherical masses.

That very law which moulds a tear,
And bids it trickle from its source,
That law preserves the earth a sphere,
And guides the planets in their course.

ROGERS.

ultimate particles of bodies, so as to produce composition and decomposition, can be sufficient to preserve the planets in their orbits*?

We can neither comprehend the one nor the other; nor can we see why the Almighty might not as easily bestow upon one species of matter the power of acting upon another when at a distancet, as the power of being acted upon and changed by matter when in actual contact‡.

Is the consideration of this universal property of matter calculated to produce any peculiar reflections?

The contemplation of this subject has a natural tendency to promote the most profound feelings of awe and admiration; for the understanding of the highest intelligencies sinks into nothing when compared with the energy of that Onnipotent Being, who had wisdom to contrive, and ability to endue the matter which he had formed, with the astonishing Power of operating upon its fellow matter either in contact, or when separated by the infinity

A passage of Dr. Watson's will perhaps furnish as good a reply to this question as can be given. "We feel the interference of the Deity every where, but we cannot apprehend the nature of his agency any where. A blade of grass cannot spring up, a drop of rain cannot fall, a ray of light cannot be emitted from the sun, nor a particle of salt be united, with a never failing symmetry to its fellow, without him; every secondary cause we discover, is but a new proof of the necessity we are under of ultimately recurring to him as the one primary cause of every thing."

+ Dr. Herschel has shown, that not only the planets in our system are preserved in their orbits by mutual attraction, but that in the sideral systems the double stars are so situated with respect to each other, that they must be subjected to mutual gravitation, and that they can only preserve their relative distances by a periodical revolution round a common centre. What he calls the insulated stars he imagines to be nearly out of the reach of mutual gravitation. He considers our sun and all the brightest stars to be of this class. They are of such immense distances, that he calculates that Sirius (the nearest of the fixt stars to us) and the Sun, if left alone would be 33 millions of years in falling together. The sam- philosopher has said, that though light travels at the astonishing velocity of 200,000 miles in a second, some of the nebula are so far from us that the rays of light must have been nearly two millions of years in passing from them to our system. According to a writer in the thirty second volume of the Monthly Review, N. S. 523, astronomers are now acquainted with no less than 2120 of these nebulous stars. Doubtless they are so many distinct worlds, appropriated by the Author of nature for the reception of intelligent beings, and for the abodes of rectitude and felicity.

Lightnings and storms His mighty word obey,

And planets roll where He has mark'd their way.

Thomson's Chymistry.

of space. Well might a writer of antiquity assert, that God saw every thing that he had made, and behold it was very good*.

Having now completed my original design of furnishing the YOUNG with an elementary treatise on chymistry, it may be necessary to apologize to some readers for the introduction of those moral reflections which so frequently occur. This cannot be done better than in the language of a late popular writer:-"Every man," says he, has a particular train of thought into which his mind falls, when at leisure from the impressions and ideas that occasionally excite it; and if one train of thinking be more desirable than another, it is surely that which regards the phenomena of nature with a constant reference to a supreme intelligent Author," Paley.

ADDITIONAL NOTES.

I. Of Specific Gravity.

HE common method of taking the specific gravity of the metals, or of

weight when weighed in air and in water; that is, to divide the absolute weight by the loss, and the quotient is the specific gravity. Thus, if a mineral which weighs three ounces in air, weighs only two ounces when weighed in water, the spec fic gravity of such mineral is 3; that is, if water, as it generally is, be called 1.000, the substance now examined is 3.000; or, to make it plain to the young student, if a pint of water weigh one pound, the same buik of the mineral will weigh three pounds. See page 38.

A more ready way to determine the specific gravity of solids is to fill a phial with water, and note the weight of the whole accurately in grains. Then weigh 100 grains of the mineral or other substance to be exam ned, and drop it gradually into the phial of water. The difference of weight of the bottle with its contents now, and when it was filled with water only, will give the specific gravity of the matter under examination. For example, if the bottle weighs 50 grains more than it did when it was filled with water only, it shows that 100 grains of the mineral displace only 50 grains of water, and consequently that it is twice the specific gravity of water. This method is said to have been discovered by Archimedes. See Note, page 35. The specific gravity of fluids is generally determined by an areometer, which is a graduated glass tube with a bulb, so contrived that it may swim in the fluid in a perpendicular position. The specific gravity is shown by the degree to which this instrument sinks in the fluid to be examined, and this will consequently always be lower in proportion as the liquid is lighter. The specific gravity of ardent spirits is generally ascertained by means of an hydrometer, of which various kinds are sold by the mathematical instrument makers.

The following method, which was contrived by Dr. Lewis, the celebrated author of the Commercium Philosophico-Technicum, and which was communicated to me by the amiable Samuel Moore, esq. late secretary to the Society for the promotion of arts, manufactures, and commerce, I prefer to every other