a candle, and that of a lamp, both produce water and carbonic acid gas. Can you tell me how these are formed?

Emily. Let me think . . . . . Both the candle and lamp burn by means of fixed oil-this is decomposed as the combustion goes on; and the constituent parts of the oil being thus separated, the carbone unites to a portion of oxygen from the atmosphere to form carbonic acid gas, whilst the hydrogen combines with another portion of oxygen, and forms with it water. The products therefore, of the combustion of oils, are water and carbonic acid gas.

Caroline. But we see neither water nor carbonic acid produced by the combustion of a candle?

Mrs. B. The carbonic acid gas, you know is invisible, and the water being in a state of vapour, is so likewise. Emily is perfectly correct in her explanation, and I am very much pleased with it,

All the vegetable acids consist of various proportions of carbone and hydrogen, acidified by oxygen. Gums, sugar, and starch, are likewise composed of these ingredients; but as the oxygen which they contain is not sufficient to convert them into acids, they are classed with the oxyds, and called vegetable oxyds.

Emily. I am very much delighted with all these new ideas; but at the same time, I cannot help being apprehensive that I may forget many of them,

Mrs. B. I would advise you to take notes, or, what would answer better still, to write down, after every lesson, as much of it as you can recollect. And, in order to give you a little assistance, I shall lend you the heads or index, which I occasionally consult for the sake of preserving some method and arrangement in these conversations. Unless you follow some such plan, you cannot expect to retain nearly all that you learn, how great soever be the impression it may make on you at first,

Emily. I will certainly follow your advice. Hither to I have found that I recollected pretty well what you have taught us; but the history of carbone is a more

extensive subject than any of the simple bodies we have yet examined.

Mrs. B. I have little more to say on carbone at present, but hereafter you will see that it performs a considerable part in most chemical operations.

Caroline. That is, I suppose, owing to its entering into the composition of so great a variety of substances? Mrs. B. Certainly; it is the basis, you have seen, of all vegetable matter; and you will find that it is very essential to the process of animalization. But in the mineral kingdom also, particularly in its form of carbonic acid, we shall often discover it combined with a great variety of substances.

In chemical operations, carbone is particularly useful, from its very great attraction for oxygen, as it will absorb this substance from many oxygenated or burnt bodies, and thus deoxygenate, or unburn them, and restore them to their original combustible state.

Caroline. I do not understand how a body can be unburnt, and restored to its original state. This piece of tinder, for instance, that has been burnt, if by any means the oxygen was extracted from it, would not be restored to its former state of linen; for its texture is destroyed by burning, and that must be the case with all organized or manufactured substances, as you observed in a former conversation.

Mrs. B. A compound body is decomposed by com bustion, in a way which generally precludes the possibility of restoring it to its former state; the oxygen, for instance, does not become fixed in the tinder, but it combines with its volatile parts, and flies off in the shape of gas, or watery vapour. You see therefore, how vain it would be to attempt the recomposition of such bodies. But, with regard to simple bodies, or at least bodies whose constituents are not disturbed by the process of oxygenation or deoxygenation, it is often possible to restore them, after combustion to their orig inal state. The metals, for instance, undergo no other alteration by combustion than a combination with oxygen; therefore, when the oxygen is taken from them, they return to their pure metallic state. But I

shall say nothing further of this at present, as the metals will furnish ample subject for another morning; and they are the class of simple bodies that come next under our consideration.

Conversation IX.

On Metals.

Mrs. B.

THE metals, which we are now to examine, are bodies of a very different nature from those which we have hitherto considered, They do not, like the elements of gasses, elude the immediate observation of our senses for they are the most brilliant, the most ponderous, and the most palpable substances in nature.

Caroline. I doubt, however, whether the metals will appear to us so interesting, and give us so much entertainment as those mysterious elements which conceal themselves from our view. Besides, they cannot af ford so much novelty; they are bodies with which we are already so well acquainted.

Mrs. B. But the acquaintance, you will soon per. ceive, is but very superficial; and I trust that you will find both novelty and entertainment in considering the metals in a chemical point of view. To treat of this subject fully, would require a whole course of lectures; for metals form of themselves a most important branch of practical chemistry. We must, therefore, confine ourselves to a general view of them. These bodies are seldom found naturally in their metallic form; they are generally more or less oxygenated or combined with sulphur, earths, or acids, and are often blended with each other. They are found buried in the bowels of

the earth in most parts of the globe, but chiefly in mountainous districts, where the surface of the globe has suffered from earthquakes, volcanoes, and other convulsions of nature. They are there spread in strata or beds, called veins, and these veins are composed of a certain quantity of metal, combined with various earthy substances, with which they form minerals of different nature and appearance, which are called ores.

Caroline. I am now amongst old acquaintance, for my father has a lead mine in Yorkshire, and I have heard a great deal about veins of ore, and of the roast ing and smelting of the lead; but, I confess, that I do not understand in what these operations consist.

Mrs. B. Roasting is the process by which the volatile parts of the ore are evaporated; smelting, that by which the pure metal is afterwards separated from the earthy remains of the ore. This is done by throwing the whole into a furnace, and mixing with it certain substances, that will combine with the earthy parts, and other foreign ingredients of the ore; the metal being the heaviest, falls to the bottom, and runs out by proper openings, in its pure metallic state.

Emily. You told us in a preceding lesson that metals had a strong affinity for oxygen. Do they not, therefore, combine with oxygen, when strongly heated in the furnace, and run out in the state of oxyds?

Mrs. B. No; for the scoriæ, or oxyd, which soon forms on the surface of the fused metal, when it is oxydable, prevents the air from having any further influence on the mass; so that neither combustion nor oxygenation can take place.

Caroline. Are all the metals combustible?

Mrs. B. Yes, without exception; but their attrac⚫ tion for oxygen varies extremely there are some tha will combine with it only at a very high temperature, or by the assistance of acids; whilst there are others that oxydate of themselves very rapidly, even at the lowest temperature, as manganese, which scarcely ever exists in its metallic state, as it immediately ab sorbs oxygen on being exposed to the air, and crum bles to an oxyd in the course of a few hours.

Emily. Is it not from that oxyd that you extracted

?

the oxygen gas Mrs. B. It is; so that, you see, this metal attracts oxygen at a low temperature, and parts with it when strongly heated.

Emily. Is there any other metal that oxydates at the temperature of the atmosphere?

Mrs. B. They all do, more or less, excepting gold, silver, and platina.

Copper, lead, and iron, oxydate slowly in the air, and cover themselves with a sort of rust, a process which depends on the gradual conversion of the surface into an oxyd. This rusty surface preserves the interior metal from oxydation, as it prevents the air from coming in contact with it. Strictly speaking, however, the word rust applies only to the oxyd, which forms on the surface of iron, when exposed to air and moisture, which oxyd appears to be united with a small portion of carbonic acid.

Emily. When metals oxydate from the atmosphere without an elevation of temperature, some light and heat, I suppose, must be disengaged, though not in sufficient quantities to be sensible.

Mrs. B. Undoubtedly; and, indeed, it is not surprising that in this case the light and heat should not be sensible, when you consider how extremely slow, and, indeed, how imperfectly, most metals oxydate by mere exposure to the atmosphere. For the quantity of oxygen with which metals are capable of combining, generally depends upon their temperature; and the absorption stops at various points of oxydation, according to the degree to which their temperature is raised.

Emily. That seems very natural; for the greater the quantity of caloric introduced into a metal, the further its particles are separated from one another, and the more easily, therefore, can they attract the oxygen and combine with it.

Mrs. B. Certainly; and besides, in proportion as the resistance diminishes on one hand, the affinity increases on the other. When the metal oxygenates