CONVERSATION VIII.
ON SULPHUR AND PHOSPHORUS.

----

MRS. B.

Sulphur is the next substance that comes under our consideration. It differs in one essential point from the preceding, as it exists in a solid form at the temperature of the atmosphere.

CAROLINE.

I am glad that we have at last a solid body to examine; one that we can see and touch. Pray, is it not with sulphur that the points of matches are covered, to make them easily kindle?

MRS. B.

Yes, it is; and you therefore already know that sulphur is a very combustible substance. It is seldom discovered in nature in a pure unmixed state; so great is its affinity for other substances, that it is almost constantly found combined with some of them. It is most commonly united with metals, under various forms, and is separated from them by a very simple process. It exists likewise in many mineral waters, and some vegetables yield it in various proportions, especially those of the cruciform tribe. It is also found in animal matter; in short, it may be discovered in greater or less quantity, in the mineral, vegetable, and animal kingdoms.

EMILY.

I have heard of flowers of sulphur, are they the produce of any plant?

MRS. B.

By no means: they consist of nothing more than common sulphur, reduced to a very fine powder by a process called sublimation.—You see some of it in this phial; it is exactly the same substance as this lump of sulphur, only its colour is a paler yellow, owing to its state of very minute division.

EMILY.

Pray what is sublimation?

MRS. B.

It is the evaporation, or, more properly speaking, the volatilisation of solid substances, which, in cooling, condense again in a concrete form. The process, in this instance, must be performed in a closed vessel, both to prevent combustion, which would take place if the access of air were not carefully precluded, and likewise in order to collect the substance after the operation. As it is rather a slow process, we shall not try the experiment now; but you will understand it perfectly if I show you the apparatus used for the purpose. (Plate XI. fig. 1.) Some lumps of sulphur are put into a receiver of this kind, which is called a cucurbit. Its shape, you see, somewhat resembles that of a pear, and is open at the top, so as to adapt itself exactly to a kind of conical receiver of this sort, called the head. The cucurbit, thus covered with its head, is placed over a sand-bath; this is nothing more than a vessel full of sand, which is kept heated by a furnace, such as you see here, so as to preserve the apparatus in a moderate and uniform temperature. The sulphur then soon begins to melt, and immediately after this, a thick white smoke rises, which is gradually deposited within the head, or upper part of the apparatus, where it condenses against the sides, somewhat in the form of a vegetation, whence it has obtained the name of flowers of sulphur. This apparatus, which is called an alembic, is highly useful in all kinds of distillations, as you will see when we come to treat of those operations. Alembics are not commonly made of glass, like this, which is applicable only to distillations upon a very small scale. Those used in manufactures are generally made of copper, and are, of course, considerably larger. The principal construction, however, is always the same, although their shape admits of some variation.

Plate XI.

Vol. I. p. 237.

see text and caption

Fig. 1.   A Alembic.   B Sand-bath.   C Furnace.
Fig. 2.   Eudiometer.
Fig. 3.   A Retort containing water.   B Lamp to heat the water.   C.C Porcelain tube containing Carbone.   D Furnace through which the tube passes.   E Receiver for the gas produced.   F Water bath.

Larger view

CAROLINE.

What is the use of that neck, or tube, which bends down from the upper piece of the apparatus?

MRS. B.

It is of no use in sublimations; but in distillations (the general object of which is to evaporate, by heat, in closed vessels, the volatile parts of a compound body, and to condense them again into a liquid,) it serves to carry off the condensed fluid, which otherwise would fall back into the cucurbit. But this is rather foreign to our present subject. Let us return to the sulphur. You now perfectly understand, I suppose, what is meant by sublimation?

EMILY.

I believe I do. Sublimation appears to consist in destroying, by means of heat, the attraction of aggregation of the particles of a solid body, which are thus volatilised; and as soon as they lose the caloric which produced that effect, they are deposited in the form of a fine powder.

CAROLINE.

It seems to me to be somewhat similar to the transformation of water into vapour, which returns to its liquid state when deprived of caloric.

EMILY.

There is this difference, however, that the sulphur does not return to its former state, since, instead of lumps, it changes to a fine powder.

MRS. B.

Chemically speaking, it is exactly the same substance, whether in the form of lump or powder. For if this powder be melted again by heat, it will, in cooling, be restored to the same solid state in which it was before its sublimation.

CAROLINE.

But if there be no real change, produced by the sublimation of the sulphur, what is the use of that operation?

MRS. B.

It divides the sulphur into very minute parts, and thus disposes it to enter more readily into combination with other bodies. It is used also as a means of purification.

CAROLINE.

Sublimation appears to me like the beginning of combustion, for the completion of which one circumstance only is wanting, the absorption of oxygen.

MRS. B.

But that circumstance is every thing. No essential alteration is produced in sulphur by sublimation; whilst in combustion it combines with the oxygen, and forms a new compound totally different in every respect from sulphur in its pure state.—We shall now burn some sulphur, and you will see how very different the result will be. For this purpose I put a small quantity of flowers of sulphur into this cup, and place it in a dish, into which I have poured a little water: I now set fire to the sulphur with the point of this hot wire; for its combustion will not begin unless its temperature be considerably raised.—You see that it burns with a faint blueish flame; and as I invert over it this receiver, white fumes arise from the sulphur, and fill the vessel.—You will soon perceive that the water is rising within the receiver, a little above its level in the plate.—Well, Emily, can you account for this?

EMILY.

I suppose that the sulphur has absorbed the oxygen from the atmospherical air within the receiver, and that we shall find some oxygenated sulphur in the cup. As for the white smoke, I am quite at a loss to guess what it may be.

MRS. B.

Your first conjecture is very right: but you are mistaken in the last; for nothing will be left in the cup. The white vapour is the oxygenated sulphur, which assumes the form of an elastic fluid of a pungent and offensive smell, and is a powerful acid. Here you see a chemical combination of oxygen and sulphur, producing a true gas, which would continue such under the pressure and at the temperature of the atmosphere, if it did not unite with the water in the plate, to which it imparts its acid taste, and all its acid properties.—You see, now, with what curious effects the combustion of sulphur is attended.

CAROLINE.

This is something quite new; and I confess that I do not perfectly understand why the sulphur turns acid.

MRS. B.

It is because it unites with oxygen, which is the acidifying principle. And, indeed, the word oxygen is derived from two Greek words signifying to produce an acid.

CAROLINE.

Why, then, is not water, which contains such a quantity of oxygen, acid?

MRS. B.

Because hydrogen, which is the other constituent of water, is not susceptible of acidification.—I believe it will be necessary, before we proceed further, to say a few words of the general nature of acids, though it is rather a deviation from our plan of examining the simple bodies separately, before we consider them in a state of combination.

Acids may be considered as a peculiar class of burnt bodies, which during their combustion, or combination with oxygen, have acquired very characteristic properties. They are chiefly discernible by their sour taste, and by turning red most of the blue vegetable colours. These two properties are common to the whole class of acids; but each of them is distinguished by other peculiar qualities. Every acid consists of some particular substance, (which constitutes its basis, and is different in each,) and of oxygen, which is common to them all.

EMILY.

But I do not clearly see the difference between acids and oxyds.

MRS. B.

Acids were, in fact, oxyds, which, by the addition of a sufficient quantity of oxygen, have been converted into acids. For acidification, you must observe, always implies previous oxydation, as a body must have combined with the quantity of oxygen requisite to constitute it an oxyd, before it can combine with the greater quantity that is necessary to render it an acid.

CAROLINE.

Are all oxyds capable of being converted into acids?

MRS. B.

Very far from it; it is only certain substances which will enter into that peculiar kind of union with oxygen that produces acids, and the number of these is proportionally very small; but all burnt bodies may be considered as belonging either to the class of oxyds, or to that of acids. At a future period, we shall enter more at large into this subject. At present, I have but one circumstance further to point out to your observation respecting acids: it is, that most of them are susceptible of two degrees of acidification, according to the different quantities of oxygen with which their basis combines.

EMILY.

And how are these two degrees of acidification distinguished?

MRS. B.

By the peculiar properties which result from them. The acid we have just made is the first or weakest degree of acidification, and is called sulphureous acid; if it were fully saturated with oxygen, it would be called sulphuric acid. You must therefore remember, that in this, as in all acids, the first degree of acidification is expressed by the termination in ous; the stronger, by the termination in ic.

CAROLINE.

And how is the sulphuric acid made?

MRS. B.

By burning sulphur in pure oxygen gas, and thus rendering its combustion much more complete. I have provided some oxygen gas for this purpose; it is in that bottle, but we must first decant the gas into the glass receiver which stands on the shelf in the bath, and is full of water.

CAROLINE.

Pray, let me try to do it, Mrs. B.

MRS. B.

It requires some little dexterity—hold the bottle completely under water, and do not turn the mouth upwards, till it is immediately under the aperture in the shelf, through which the gas is to pass into the receiver, and then turn it up gradually.—Very well, you have only let a few bubbles escape, and that must be expected at a first trial.—Now I shall put this piece of sulphur into the receiver, through the opening at the top, and introduce along with it a small piece of lighted tinder to set fire to it.—This requires being done very quickly, lest the atmospherical air should get in, and mix with the pure oxygen gas.

EMILY.

How beautifully it burns!

CAROLINE.

But it is already buried in the thick vapour. This, I suppose, is sulphuric acid?

EMILY.

Are these acids always in a gaseous state?

MRS. B.

Sulphureous acid, as we have already observed, is a permanent gas, and can be obtained in a liquid form only by condensing it in water. In its pure state, the sulphureous acid is invisible, and it now appears in the form of a white smoke, from its combining with the moisture. But the vapour of sulphuric acid, which you have just seen to rise during the combustion, is not a gas, but only a vapour, which condenses into liquid sulphuric acid, by losing its caloric. But it appears from Sir H. Davy’s experiments, that this formation and condensation of sulphuric acid requires the presence of water, for which purpose the vapour is received into cold water, which may afterwards be separated from the acid by evaporation.

Sulphur has hitherto been considered as a simple substance; but Sir H. Davy has suspected that it contains a small portion of hydrogen, and perhaps also of oxygen.

On submitting sulphur to the action of the Voltaic battery, he observed that the negative wire gave out hydrogen; and the existence of hydrogen in sulphur was rendered still more probable by his observing that a small quantity of water was produced during the combustion of sulphur.

EMILY.

And pray of what nature is sulphur when perfectly pure?

MRS. B.

Sulphur has probably never been obtained perfectly free from combination, so that its radical may possibly possess properties very different from those of common sulphur. It has been suspected to be of a metallic nature; but this is mere conjecture.

Before we quit the subject of sulphur, I must tell you that it is susceptible of combining with a great variety of substances, and especially with hydrogen, with which you are already acquainted. Hydrogen gas can dissolve a small portion of it.

EMILY.

What! can a gas dissolve a solid substance?

MRS. B.

Yes; a solid substance may be so minutely divided by heat, as to become soluble in a gas: and there are several instances of it. But you must observe, that, in this case, a chemical union or combination of the sulphur with the hydrogen gas is produced. In order to effect this, the sulphur must be strongly heated in contact with the gas; the heat reduces the sulphur to such a state of extreme division, and diffuses it so thoroughly through the gas, that they combine and incorporate together. And as a proof that there must be a chemical union between the sulphur and the gas, it is sufficient to remark that they are not separated when the sulphur loses the caloric by which it was volatilized. Besides, it is evident, from the peculiar fetid smell of this gas, that it is a new compound totally different from either of its constituents; it is called sulphuretted hydrogen gas, and is contained in great abundance in sulphureous mineral waters.

CAROLINE.

Are not the Harrogate waters of this nature?

MRS. B.

Yes; they are naturally impregnated with sulphuretted hydrogen gas, and there are many other springs of the same kind, which shows that this gas must often be formed in the bowels of the earth by spontaneous processes of nature.

CAROLINE.

And could not such waters be made artificially by impregnating common water with this gas?

MRS. B.

Yes; they can be so well imitated, as perfectly to resemble the Harrogate waters.

Sulphur combines likewise with phosphorus, and with the alkalies, and alkaline earths, substances with which you are yet unacquainted. We cannot, therefore, enter into these combinations at present. In our next lesson we shall treat of phosphorus.

EMILY.

May we not begin that subject to-day; this lesson has been so short?

MRS. B.

I have no objection, if you are not tired. What do you say, Caroline?

CAROLINE.

I am as desirous as Emily of prolonging the lesson to-day, especially as we are to enter on a new subject; for I confess that sulphur has not appeared to me so interesting as the other simple bodies.

MRS. B.

Perhaps you may find phosphorus more entertaining. You must not, however, be discouraged when you meet with some parts of a study less amusing than others; it would answer no good purpose to select the most pleasing parts, since, if we did not proceed with some method, in order to acquire a general idea of the whole, we could scarcely expect to take interest in any particular subjects.

PHOSPHORUS.

Phosphorus is considered as a simple body; though, like sulphur, it has been suspected of containing hydrogen. It was not known by the earlier chemists. It was first discovered by Brandt, a chemist of Hamburgh, whilst employed in researches after the philosopher’s stone; but the method of obtaining it remained a secret till it was a second time discovered both by Kunckel and Boyle, in the year 1680. You see a specimen of phosphorus in this phial; it is generally moulded into small sticks of a yellowish colour, as you find it here.

CAROLINE.

I do not understand in what the discovery consisted; there may be a secret method of making an artificial composition, but how can you talk of making a substance which naturally exists?

MRS. B.

A body may exist in nature so closely combined with other substances, as to elude the observation of chemists, or render it extremely difficult to obtain it in its separate state. This is the case with phosphorus, which is always so intimately combined with other substances, that its existence remained unnoticed till Brandt discovered the means of obtaining it free from other combinations. It is found in all animal substances, and is now chiefly extracted from bones, by a chemical process. It exists also in some plants, that bear a strong analogy to animal matter in their chemical composition.

EMILY.

But is it never found in its pure separate state?

MRS. B.

Never, and this is the reason that it has remained so long undiscovered.

Phosphorus is eminently combustible; it melts and takes fire at the temperature of one hundred degrees, and absorbs in its combustion nearly once and a half its own weight of oxygen.

CAROLINE.

What! will a pound of phosphorus consume a pound and half of oxygen?

MRS. B.

So it appears from accurate experiments. I can show you with what violence it combines with oxygen, by burning some of it in that gas. We must manage the experiment in the same manner as we did the combustion of sulphur. You see I am obliged to cut this little bit of phosphorus under water, otherwise there would be danger of its taking fire by the heat of my fingers. I now put into the receiver, and kindle it by means of a hot wire.

EMILY.

What a blaze! I can hardly look at it. I never saw any thing so brilliant. Does it not hurt your eyes, Caroline?

CAROLINE.

Yes; but still I cannot help looking at it. A prodigious quantity of oxygen must indeed be absorbed, when so much light and caloric are disengaged!

MRS. B.

In the combustion of a pound of phosphorus, a sufficient quantity of caloric is set free to melt upwards of a hundred pounds of ice; this has been computed by direct experiments with the calorimeter.

EMILY.

And is the result of this combustion, like that of sulphur, an acid?

MRS. B.

Yes; phosphoric acid. And had we duly proportioned the phosphorus and the oxygen, they would have been completely converted into phosphoric acid, weighing together, in this new state, exactly the sum of their weights separately. The water would have ascended into the receiver, on account of the vacuum formed, and would have filled it entirely. In this case, as in the combustion of sulphur, the acid vapour formed is absorbed and condensed in the water of the receiver. But when this combustion is performed without any water or moisture being present, the acid then appears in the form of concrete whitish flakes, which are, however, extremely ready to melt upon the least admission of moisture.

EMILY.

Does phosphorus, in burning in atmospherical air, produce, like sulphur, a weaker sort of the same acid?

MRS. B.

No: for it burns in atmospherical air, nearly at the same temperature as in pure oxygen gas; and it is in both cases so strongly disposed to combine with the oxygen, that the combustion is perfect, and the product similar; only in atmospherical air, being less rapidly supplied with oxygen, the process is performed in a slower manner.

CAROLINE.

But is there no method of acidifying phosphorus in a slighter manner, so as to form phosphorus acid?

MRS. B.

Yes, there is. When simply exposed to the atmosphere, phosphorus undergoes a kind of slow combustion at any temperature above zero.

EMILY.

But is not the process in this case rather an oxydation than a combustion? For if the oxygen is too slowly absorbed for a sensible quantity of light and heat to be disengaged, it is not a true combustion.

MRS. B.

The case is not as you suppose: a faint light is emitted which is very discernible in the dark; but the heat evolved is not sufficiently strong to be sensible: a whitish vapour arises from this combustion, which, uniting with water, condenses into liquid phosphorus acid.

CAROLINE.

Is it not very singular that phosphorus should burn at so low a temperature in atmospherical air, whilst it does not burn in pure oxygen without the application of heat?

MRS. B.

So it at first appears. But this circumstance seems to be owing to the nitrogen gas of the atmosphere. This gas dissolves small particles of phosphorus, which being thus minutely divided and diffused in the atmospherical air, combines with the oxygen, and undergoes this slow combustion. But the same effect does not take place in oxygen gas, because it is not capable of dissolving phosphorus; it is therefore necessary, in this case, that heat should be applied to effect that division of particles, which, in the former instance, is produced by the nitrogen.

EMILY.

I have seen letters written with phosphorus, which are invisible by day-light, but may be read in the dark by their own light. They look as if they were written with fire; yet they do not seem to burn.

MRS. B.

But they do really burn; for it is by their slow combustion that the light is emitted; and phosphorus acid is the result of this combustion.

Phosphorus is sometimes used as a test to estimate the purity of atmospherical air. For this purpose, it is burnt in a graduated tube, called an Eudiometer (Plate XI. fig. 2.), and from the quantity of air which the phosphorus absorbs, the proportion of oxygen in the air examined is deduced; for the phosphorus will absorb all the oxygen, and the nitrogen alone will remain.

EMILY.

And the more oxygen is contained in the atmosphere, the purer, I suppose, it is esteemed?

MRS. B.

Certainly. Phosphorus, when melted, combines with a great variety of substances. With sulphur it forms a compound so extremely combustible, that it immediately takes fire on coming in contact with the air. It is with this composition that phosphoric matches are prepared, which kindle as soon as they are taken out of their case and are exposed to the air.

EMILY.

I have a box of these curious matches; but I have observed, that in very cold weather, they will not take fire without being previously rubbed.

MRS. B.

By rubbing them you raise their temperature; for, you know, friction is one of the means of extricating heat.

EMILY.

Will phosphorus combine with hydrogen gas, as sulphur does?

MRS. B.

Yes; and the compound gas which results from this combination has a smell still more fetid than the sulphuretted hydrogen; it resembles that of garlic.

The phosphoretted hydrogen gas has this remarkable peculiarity, that it takes fire spontaneously in the atmosphere, at any temperature. It is thus, probably, that are produced those transient flames, or flashes of light, called by the vulgar Will-of-the Whisp, or more properly Ignes-fatui, which are often seen in church-yards, and places where the putrefactions of animal matter exhale phosphorus and hydrogen gas.

CAROLINE.

Country people, who are so much frightened by those appearances, would soon be reconciled to them, if they knew from what a simple cause they proceed.

MRS. B.

There are other combinations of phosphorus that have also very singular properties, particularly that which results from its union with lime.

EMILY.

Is there any name to distinguish the combination of two substances, like phosphorus and lime, neither of which are oxygen, and which cannot therefore produce either an oxyd or an acid?

MRS. B.

The names of such combinations are composed from those of their ingredients, merely by a slight change in their termination. Thus the combination of sulphur with lime is called a sulphuret, and that of phosphorus, a phosphuret of lime. This latter compound, I was going to say, has the singular property of decomposing water, merely by being thrown into it. It effects this by absorbing the oxygen of water, in consequence of which bubbles of hydrogen gas ascend, holding in solution a small quantity of phosphorus.

EMILY.

These bubbles then are phosphoretted hydrogen gas?

MRS. B.

Yes; and they produce the singular appearance of a flash of fire issuing from water, as the bubbles kindle and detonate on the surface of the water, at the instant that they come in contact with the atmosphere.

CAROLINE.

Is not this effect nearly similar to that produced by the combination of phosphorus and sulphur, or, more properly speaking, the phosphuret of sulphur?

MRS. B.

Yes; but the phenomenon appears more extraordinary in this case, from the presence of water, and from the gaseous form of the combustible compound. Besides, the experiment surprises by its great simplicity. You only throw a piece of phosphoret of lime into a glass of water, and bubbles of fire will immediately issue from it.

CAROLINE.

Cannot we try the experiment?

MRS. B.

Very easily: but we must do it in the open air; for the smell of the phosphorated hydrogen gas is so extremely fetid, that it would be intolerable in the house. But before we leave the room, we may produce, by another process, some bubbles of the same gas, which are much less offensive.

There is in this little glass retort a solution of potash in water; I add to it a small piece of phosphorus. We must now heat the retort over the lamp, after having engaged its neck under water—you see it begins to boil; in a few minutes bubbles will appear, which take fire and detonate as they issue from the water.

CAROLINE.

There is one—and another. How curious it is!—But I do not understand how this is produced.

MRS. B.

It is the consequence of a display of affinities too complicated, I fear, to be made perfectly intelligible to you at present.

In a few words, the reciprocal action of the potash, phosphorus, caloric, and water are such, that some of the water is decomposed, and the hydrogen gas thereby formed carries off some minute particles of phosphorus, with which it forms phosphoretted hydrogen gas, a compound which spontaneously takes fire at almost any temperature.

EMILY.

What is that circular ring of smoke which slowly rises from each bubble after its detonation? 

MRS. B.

It consists of water and phosphoric acid in vapour, which are produced by the combustion of hydrogen and phosphorus.

CONVERSATION IX.
ON CARBON.

----

CAROLINE.

To-day, Mrs. B., I believe we are to learn the nature and properties of CARBON. This substance is quite new to me; I never heard it mentioned before.

MRS. B.

Not so new as you imagine; for carbon is nothing more than charcoal in a state of purity, that is to say, unmixed with any foreign ingredients.

CAROLINE.

But charcoal is made by art, Mrs. B., and a body consisting of one simple substance cannot be fabricated?

MRS. B.

You again confound the idea, of making a simple body, with that of separating it from a compound. The chemical processes by which a simple body is obtained in a state of purity, consist in unmaking the compound in which it is contained, in order to separate from it the simple substance in question. The method by which charcoal is usually obtained, is, indeed, commonly called making it; but, upon examination, you will find this process to consist simply in separating it from other substances with which it is found combined in nature.

Carbon forms a considerable part of the solid matter of all organised bodies; but it is most abundant in the vegetable creation, and it is chiefly obtained from wood. When the oil and water (which are other constituents of vegetable matter) are evaporated, the black, porous, brittle substance that remains, is charcoal.

CAROLINE.

But if heat be applied to the wood in order to evaporate the oil and water, will not the temperature of the charcoal be raised so as to make it burn; and if it combines with oxygen, can we any longer call it pure?

MRS. B.

I was going to say, that, in this operation, the air must be excluded.

CAROLINE.

How then can the vapour of the oil and water fly off?

MRS. B.

In order to produce charcoal in its purest state (which is, even then, but a less imperfect sort of carbon), the operation should be performed in an earthen retort. Heat being applied to the body of the retort, the evaporable part of the wood will escape through its neck, into which no air can penetrate as long as the heated vapour continues to fill it. And if it be wished to collect these volatile products of the wood, this can easily be done by introducing the neck of the retort into the water-bath apparatus, with which you are acquainted. But the preparation of common charcoal, such as is used in kitchens and manufactures, is performed on a much larger scale, and by an easier and less expensive process.

EMILY.

I have seen the process of making common charcoal. The wood is ranged on the ground in a pile of a pyramidical form, with a fire underneath; the whole is then covered with clay, a few holes only being left for the circulation of air.

MRS. B.

These holes are closed as soon as the wood is fairly lighted, so that the combustion is checked, or at least continues but in a very imperfect manner; but the heat produced by it is sufficient to force out and volatilize, through the earthy cover, most part of the oily and watery principles of the wood, although it cannot reduce it to ashes.

EMILY.

Is pure carbon as black as charcoal?

MRS. B.

The purest charcoal we can prepare is so; but chemists have never yet been able to separate it entirely from hydrogen. Sir H. Davy says, that the most perfect carbon that is prepared by art contains about five per cent. of hydrogen; he is of opinion, that if we could obtain it quite free from foreign ingredients, it would be metallic, in common with other simple substances.

But there is a form in which charcoal appears, that I dare say will surprise you.—This ring, which I wear on my finger, owes its brilliancy to a small piece of carbon.

CAROLINE.

Surely, you are jesting, Mrs. B.?

EMILY.

I thought your ring was diamond?

MRS. B.

It is so. But diamond is nothing more than carbon in a crystallized state.

EMILY.

That is astonishing! Is it possible to see two things apparently more different than diamond and charcoal?

CAROLINE.

It is, indeed, curious to think that we adorn ourselves with jewels of charcoal!

MRS. B.

There are many other substances, consisting chiefly of carbon, that are remarkably white. Cotton, for instance, is almost wholly carbon.

CAROLINE.

That, I own, I could never have imagined!—But pray, Mrs. B., since it is known of what substance diamond and cotton are composed, why should they not be manufactured, or imitated, by some chemical process, which would render them much cheaper, and more plentiful than the present mode of obtaining them?

MRS. B.

You might as well, my dear, propose that we should make flowers and fruit, nay, perhaps even animals, by a chemical process; for it is known of what these bodies consist, since every thing which we are acquainted with in nature is formed from the various simple substances that we have enumerated. But you must not suppose that a knowledge of the component parts of a body will in every case enable us to imitate it. It is much less difficult to decompose bodies, and discover of what materials they are made, than it is to recompose them. The first of these processes is called analysis, the last synthesis. When we are able to ascertain the nature of a substance by both these methods, so that the result of one confirms that of the other, we obtain the most complete knowledge of it that we are capable of acquiring. This is the case with water, with the atmosphere, with most of the oxyds, acids, and neutral salts, and with many other compounds. But the more complicated combinations of nature, even in the mineral kingdom, are in general beyond our reach, and any attempt to imitate organised bodies must ever prove fruitless; their formation is a secret that rests in the bosom of the Creator. You see, therefore, how vain it would be to attempt to make cotton by chemical means. But, surely, we have no reason to regret our inability in this instance, when nature has so clearly pointed out a method of obtaining it in perfection and abundance.

CAROLINE.

I did not imagine that the principle of life could be imitated by the aid of chemistry; but it did not appear to me ridiculous to suppose that chemists might attain a perfect imitation of inanimate nature.

MRS. B.

They have succeeded in this point in a variety of instances; but, as you justly observe, the principle of life, or even the minute and intimate organisation of the vegetable kingdom, are secrets that have almost entirely eluded the researches of philosophers; nor do I imagine that human art will ever be capable of investigating them with complete success.

EMILY.

But diamond, since it consists of one simple unorganised substance, might be, one would think, perfectly imitable by art?

MRS. B.

It is sometimes as much beyond our power to obtain a simple body in a state of perfect purity, as it is to imitate a complicated combination; for the operations by which nature separates bodies are frequently as inimitable as those which she uses for their combination. This is the case with carbon; all the efforts of chemists to separate it entirely from other substances have been fruitless, and in the purest state in which it can be obtained by art, it still retains a portion of hydrogen, and probably of some other foreign ingredients. We are ignorant of the means which nature employs to crystallize it. It may probably be the work of ages, to purify, arrange, and unite the particles of carbon in the form of diamond. Here is some charcoal in the purest state we can procure it: you see that it is a very black, brittle, light, porous substance, entirely destitute of either taste or smell. Heat, without air, produces no alteration in it, as it is not volatile; but, on the contrary, it invariably remains at the bottom of the vessel after all the other parts of the vegetable are evaporated.

EMILY.

Yet carbon is, no doubt, combustible, since you say that charcoal would absorb oxygen if air were admitted during its preparation?

CAROLINE.

Unquestionably. Besides, you know, Emily, how much it is used in cooking. But pray what is the reason that charcoal burns without smoke, whilst a wood fire smokes so much?

MRS. B.

Because, in the conversion of wood into charcoal, the volatile particles of the former have been evaporated.

CAROLINE.

Yet I have frequently seen charcoal burn with flame; therefore it must, in that case, contain some hydrogen.

MRS. B.

Very true; but you must recollect that charcoal, especially that which is used for common purposes, is not perfectly pure. It generally retains some remains of the various other component parts of vegetables, and hydrogen particularly, which accounts for the flame in question.

CAROLINE.

But what becomes of the carbon itself during its combustion?

MRS. B.

It gradually combines with the oxygen of the atmosphere, in the same way as sulphur and phosphorus, and, like those substances, it is converted into a peculiar acid, which flies off in a gaseous form. There is this difference, however, that the acid is not, in this instance, as in the two cases just mentioned, a mere condensable vapour, but a permanent elastic fluid, which always remains in the state of gas, under any pressure and at any temperature. The nature of this acid was first ascertained by Dr. Black, of Edinburgh; and, before the introduction of the new nomenclature, it was called fixed air. It is now distinguished by the more appropriate name of carbonic acid gas.

EMILY.

Carbon, then, can be volatilized by burning, though, by heat alone, no such effect is produced?

MRS. B.

Yes; but then it is no longer simple carbon, but an acid of which carbon forms the basis. In this state, carbon retains no more appearance of solidity or corporeal form, than the basis of any other gas. And you may, I think, from this instance, derive a more clear idea of the basis of the oxygen, hydrogen, and nitrogen gases, the existence of which, as real bodies, you seemed to doubt, because they were not to be obtained simply in a solid form.

EMILY.

That is true; we may conceive the basis of the oxygen, and of the other gases, to be solid, heavy substances, like carbon; but so much expanded by caloric as to become invisible.

CAROLINE.

But does not the carbonic acid gas partake of the blackness of charcoal?

MRS. B.

Not in the least. Blackness, you know, does not appear to be essential to carbon, and it is pure carbon, and not charcoal, that we must consider as the basis of carbonic acid. We shall make some carbonic acid, and, in order to hasten the process, we shall burn the carbon in oxygen gas.

EMILY.

But do you mean then to burn diamond?

MRS. B.

Charcoal will answer the purpose still better, being softer and more easy to inflame; besides the experiments on diamond are rather expensive.

CAROLINE.

But is it possible to burn diamond?

MRS. B.

Yes, it is; and in order to effect this combustion, nothing more is required than to apply a sufficient degree of heat by means of the blow-pipe, and of a stream of oxygen gas. Indeed it is by burning diamond that its chemical nature has been ascertained. It has long been known as a combustible substance, but it is within these few years only that the product of its combustion has been proved to be pure carbonic acid. This remarkable discovery is due to Mr. Tennant.

Now let us try to make some carbonic acid.—Will you, Emily, decant some oxygen gas from this large jar into the receiver in which we are to burn the carbon; and I shall introduce this small piece of charcoal, with a little lighted tinder, which will be necessary to give the first impulse to the combustion.

EMILY.

I cannot conceive how so small a piece of tinder, and that but just lighted, can raise the temperature of the carbon sufficiently to set fire to it; for it can produce scarcely any sensible heat, and it hardly touches the carbon.

MRS. B.

The tinder thus kindled has only heat enough to begin its own combustion, which, however, soon becomes so rapid in the oxygen gas, as to raise the temperature of the charcoal sufficiently for this to burn likewise, as you see is now the case.

EMILY.

I am surprised that the combustion of carbon is not more brilliant; it does not give out near so much light or caloric as phosphorus, or sulphur. Yet since it combines with so much oxygen, why is not a proportional quantity of light and heat disengaged from the decomposition of the oxygen gas, and the union of its electricity with that of the charcoal?

MRS. B.

It is not surprising that less light and heat should be liberated in this than in almost any other combustion, since the oxygen, instead of entering into a solid or liquid combination, as it does in the phosphoric and sulphuric acids, is employed in forming another elastic fluid; it therefore parts with less of its caloric.

EMILY.

True; and, on second consideration, it appears, on the contrary, surprising that the oxygen should, in its combination with carbon, retain a sufficient portion of caloric to maintain both substances in a gaseous state.

CAROLINE.

We may then judge of the degree of solidity in which oxygen is combined in a burnt body, by the quantity of caloric liberated during its combustion?

MRS. B.

Yes; provided that you take into the account the quantity of oxygen absorbed by the combustible body, and observe the proportion which the caloric bears to it.

CAROLINE.

But why should the water, after the combustion of carbon, rise in the receiver, since the gas within it retains an aëriform state?

MRS. B.

Because the carbonic acid gas is gradually absorbed by the water; and this effect would be promoted by shaking the receiver.

EMILY.

The charcoal is now extinguished, though it is not nearly consumed; it has such an extraordinary avidity for oxygen, I suppose, that the receiver did not contain enough to satisfy the whole.

MRS. B.

That is certainly the case; for if the combustion were performed in the exact proportions of 28 parts of carbon to 72 of oxygen, both these ingredients would disappear, and 100 parts of carbonic acid would be produced.

CAROLINE.

Carbonic acid must be a very strong acid, since it contains so great a proportion of oxygen?

MRS. B.

That is a very natural inference; yet it is erroneous. For the carbonic is the weakest of all the acids. The strength of an acid seems to depend upon the nature of its basis, and its mode of combination, as well as upon the proportion of the acidifying principle. The same quantity of oxygen that will convert some bodies into strong acids, will only be sufficient simply to oxydate others.

CAROLINE.

Since this acid is so weak, I think chemists should have called it the carbonous, instead of the carbonic acid.

EMILY.

But, I suppose, the carbonous acid is still weaker, and is formed by burning carbon in atmospherical air.

MRS. B.

It has been lately discovered, that carbon may be converted into a gas, by uniting with a smaller proportion of oxygen; but as this gas does not possess any acid properties, it is no more than an oxyd; it is called gaseous oxyd of carbon.

CAROLINE.

Pray is not carbonic acid a very wholesome gas to breathe, as it contains so much oxygen?

MRS. B.

On the contrary, it is extremely pernicious. Oxygen, when in a state of combination with other substances, loses, in almost every instance, its respirable properties, and the salubrious effects which it has on the animal economy when in its unconfined state. Carbonic acid is not only unfit for respiration, but extremely deleterious if taken into the lungs.

EMILY.

You know, Caroline, how very unwholesome the fumes of burning charcoal are reckoned.

CAROLINE.

Yes; but, to confess the truth, I did not consider that a charcoal fire produced carbonic acid gas.—Can this gas be condensed into a liquid?

MRS. B.

No: for, as I told you before, it is a permanent elastic fluid. But water can absorb a certain quantity of this gas, and can even be impregnated with it, in a very strong degree, by the assistance of agitation and pressure, as I am going to show you. I shall decant some carbonic acid gas into this bottle, which I fill first with water, in order to exclude the atmospherical air; the gas is then introduced through the water, which you see it displaces, for it will not mix with it in any quantity, unless strongly agitated, or allowed to stand over it for some time. The bottle is now about half full of carbonic acid gas, and the other half is still occupied by the water. By corking the bottle, and then violently shaking it, in this way, I can mix the gas and water together.—Now will you taste it?

EMILY.

It has a distinct acid taste.

CAROLINE.

Yes, it is sensibly sour, and appears full of little bubbles.

MRS. B.

It possesses likewise all the other properties of acids, but, of course, in a less degree than the pure carbonic acid gas, as it is so much diluted by water.

This is a kind of artificial Seltzer water. By analysing that which is produced by nature, it was found to contain scarcely any thing more than common water impregnated with a certain proportion of carbonic acid gas. We are, therefore, able to imitate it, by mixing those proportions of water and carbonic acid. Here, my dear, is an instance, in which, by a chemical process, we can exactly copy the operations of nature; for the artificial Seltzer waters can be made in every respect similar to those of nature; in one point, indeed, the former have an advantage, since they may be prepared stronger, or weaker, as occasion requires.

CAROLINE.

I thought I had tasted such water before. But what renders it so brisk and sparkling?

MRS. B.

This sparkling, or effervescence, as it is called, is always occasioned by the action of an elastic fluid escaping from a liquid; in the artificial Seltzer water, it is produced by the carbonic acid, which being lighter than the water in which it was strongly condensed, flies off with great rapidity the instant the bottle is uncorked; this makes it necessary to drink it immediately. The bubbling that took place in this bottle was but trifling, as the water was but very slightly impregnated with carbonic acid. It requires a particular apparatus to prepare the gaseous artificial mineral waters.

EMILY.

If, then, a bottle of Seltzer water remains for any length of time uncorked, I suppose it returns to the state of common water?

MRS. B.

The whole of the carbonic acid gas, or very nearly so, will soon disappear; but there is likewise in Seltzer water a very small quantity of soda, and of a few other saline or earthy ingredients, which will remain in the water, though it should be kept uncorked for any length of time.

CAROLINE.

I have often heard of people drinking soda-water. Pray what sort of water is that?

MRS. B.

It is a kind of artificial Seltzer water, holding in solution, besides the gaseous acid, a particular saline substance, called soda, which imparts to the water certain medicinal qualities.

CAROLINE.

But how can these waters be so wholesome, since carbonic acid is so pernicious?

MRS. B.

A gas, we may conceive, though very prejudicial to breathe, may be beneficial to the stomach.—But it would be of no use to attempt explaining this more fully at present.

CAROLINE.

Are waters never impregnated with other gases?

MRS. B.

Yes; there are several kinds of gaseous waters. I forgot to tell you that waters have, for some years past, been prepared, impregnated both with oxygen and hydrogen gases. These are not an imitation of nature, but are altogether obtained by artificial means. They have been lately used medicinally, particularly on the continent, where, I understand, they have acquired some reputation.

EMILY.

If I recollect right, Mrs. B., you told us that carbon was capable of decomposing water; the affinity between oxygen and carbon must, therefore, be greater than between oxygen and hydrogen?

MRS. B.

Yes; but this is not the case unless their temperature be raised to a certain degree. It is only when carbon is red-hot, that it is capable of separating the oxygen from the hydrogen. Thus, if a small quantity of water be thrown on a red-hot fire, it will increase rather than extinguish the combustion; for the coals or wood (both of which contain a quantity of carbon) decompose the water, and thus supply the fire both with oxygen and hydrogen gases. If, on the contrary, a large mass of water be thrown over the fire, the diminution of heat thus produced is such, that the combustible matter loses the power of decomposing the water, and the fire is extinguished.

EMILY.

I have heard that fire-engines sometimes do more harm than good, and that they actually increase the fire when they cannot throw water enough to extinguish it. It must be owing, no doubt, to the decomposition of the water by the carbon during the conflagration.

MRS. B.

Certainly.—The apparatus which you see here (Plate XI. fig. 3.), may be used to exemplify what we have just said. It consists in a kind of open furnace, through which a porcelain tube, containing charcoal, passes. To one end of the tube is adapted a glass retort with water in it; and the other end communicates with a receiver placed on the water-bath. A lamp being applied to the retort, and the water made to boil, the vapour is gradually conveyed through the red-hot charcoal, by which it is decomposed; and the hydrogen gas which results from this decomposition is collected in the receiver. But the hydrogen thus obtained is far from being pure; it retains in solution a minute portion of carbon, and contains also a quantity of carbonic acid. This renders it heavier than pure hydrogen gas, and gives it some peculiar properties; it is distinguished by the name of carbonated hydrogen gas.

CAROLINE.

And whence does it obtain the carbonic acid that is mixed with it?

EMILY.

I believe I can answer that question, Caroline.—From the union of the oxygen (proceeding from the decomposed water) with the carbon, which, you know, makes carbonic acid.

CAROLINE.

True; I should have recollected that.—The product of the decomposition of water by red-hot charcoal, therefore, is carbonated hydrogen gas, and carbonic acid gas.

MRS. B.

You are perfectly right now.

Carbon is frequently found combined with hydrogen in a state of solidity, especially in coals, which owe their combustible nature to these two principles.

EMILY.

Is it the hydrogen, then, that produces the flame of coals?

MRS. B.

It is so; and when all the hydrogen is consumed, the carbon continues to burn without flame. But again, as I mentioned when speaking of the gas-lights, the hydrogen gas produced by the burning of coals is not pure; for, during the combustion, particles of carbon are successively volatilized with the hydrogen, with which they form what is called a hydro-carbonat, which is the principal product of this combustion.

Carbon is a very bad conductor of heat; for this reason, it is employed (in conjunction with other ingredients) for coating furnaces and other chemical apparatus.

EMILY.

Pray what is the use of coating furnaces?

MRS. B.

In most cases, in which a furnace is used, it is necessary to produce and preserve a great degree of heat, for which purpose every possible means are used to prevent the heat from escaping by communicating with other bodies, and this object is attained by coating over the inside of the furnace with a kind of plaster, composed of materials that are bad conductors of heat.

Carbon, combined with a small quantity of iron, forms a compound called plumbago, or black-lead, of which pencils are made. This substance, agreeably to the nomenclature, is a carburet of iron.

EMILY.

Why, then, is it called black-lead?

MRS. B.

It is an ancient name given to it by ignorant people, from its shining metallic appearance; but it is certainly a most improper name for it, as there is not a particle of lead in the composition. There is only one mine of this mineral, which is in Cumberland. It is supposed to approach as nearly to pure carbon as the best prepared charcoal does, as it contains only five parts of iron, unadulterated by any other foreign ingredients. There is another carburet of iron, in which the iron, though united only to an extremely small proportion of carbon, acquires very remarkable properties; this is steel.

CAROLINE.

Really; and yet steel is much harder than iron?

MRS. B.

But carbon is not ductile like iron, and therefore may render the steel more brittle, and prevent its bending so easily. Whether it is that the carbon, by introducing itself into the pores of the iron, and, by filling them, makes the metal both harder and heavier; or whether this change depends upon some chemical cause, I cannot pretend to decide. But there is a subsequent operation, by which the hardness of steel is very much increased, which simply consists in heating the steel till it is red-hot, and then plunging it into cold water.

Carbon, besides the combination just mentioned, enters into the composition of a vast number of natural productions, such, for instance, as all the various kinds of oils, which result from the combination of carbon, hydrogen, and caloric, in various proportions.

EMILY.

I thought that carbon, hydrogen, and caloric, formed carbonated hydrogen gas?

MRS. B.

That is the case when a small portion of carbonic acid gas is held in solution by hydrogen gas. Different proportions of the same principles, together with the circumstances of their union, produce very different combinations; of this you will see innumerable examples. Besides, we are not now talking of gases, but of carbon and hydrogen, combined only with a quantity of caloric sufficient to bring them to the consistency of oil or fat.

CAROLINE.

But oil and fat are not of the same consistence?

MRS. B.

Fat is only congealed oil; or oil, melted fat. The one requires a little more heat to maintain it in a fluid state than the other. Have you never observed the fat of meat turned to oil by the caloric it has imbibed from the fire?