Tutor. Come—the tea is ready. Lay by your book, and let us talk a little. You have assisted in tea-making a great many times, and yet I dare say you never considered what kind of an operation it was.

Pupil. An operation of cookery—is it not?

Tut. You may call it so: but it is properly an operation of chymistry.

Pup. Of chymistry! I thought that had been a very deep sort of a business.

Tut. O—there are many things in common life that belong to the deepest of sciences. Making tea is the chymical operation called infusion, which is, when a hot liquor is poured upon a substance in order to extract something from it. The water, you see, extracts from the tea-leaves their colour, taste, and flavour.

Pup. Would not cold water do the same?

Tut. It would, but more slowly. Heat assists almost all liquors in their power of extracting the virtues of herbs and other substances. Thus good housewives were formerly used to boil their tea, in order to get all goodness from it as completely as possible. The greater heat and agitation of boiling make it act more powerfully. The liquor in which a substance has been boiled is called a decoction of that substance.

Pup. Then we had a decoction of mutton at dinner to-day.

Tut. We had—broth is a decoction, and so are gruel and barley-water. But when anything is put to steep in a cold liquor it is called maceration. The ingredients of which ink is made are macerated. In all these cases, you see, the whole substance does not mix with the liquor, but only part of it. The reason is, that part of it is soluble in the liquor, and part not.

Pup. What is the meaning of that?

Tut. Solution is when a solid put into a fluid entirely disappears in it, leaving the liquor clear. Thus when I throw this lump of sugar into my tea, you see it gradually wastes away till it is all gone, and then I can taste it in every single drop of my tea; but the tea is as clear as before.

Pup. Salt would do the same.

Tut. It would. But if I were to throw in a lump of chalk, it would lie undissolved at the bottom.

Pup. But it would make the water white.

Tut. True, while it was stirred; and then it would be a diffusion. But while the chalk was thus mixed with the liquor, it would lose its transparency, and not recover it again till, by standing, the chalk had all subsided and left the liquor as it was before.

Pup. How is the cream mixed with the tea?

Tut. Why, that is only diffused, for it takes away the transparency of the tea. But the particles of cream being finer and lighter than those of chalk, it remains longer united with the liquor. However, in time the cream would separate too, and rise to the top, leaving the tea clear. Now, suppose you had a mixture of sugar, salt, chalk, and tea-leaves, and were to throw it into water, either hot or cold; what would be the effect?

Pup. The sugar and salt would be dissolved and disappear. The tea-leaves would yield their colour and taste. The chalk—I do not know what would become of that.

Tut. Why, if the mixture were stirred, the chalk would be diffused through it, and make it turbid or muddy; but on standing, it would leave it unchanged.

Pup. Then there would remain at bottom the chalk and tea-leaves?

Tut. Yes. The clear liquor would contain in solution salt, sugar, and those particles of the tea in which its colour and taste consisted; the remainder of the tea and the chalk would lie undissolved.

Pup. Then I suppose tea-leaves, after the tea is made, are lighter than at first.

Tut. Undoubtedly. If taken out and dried they would be found to have lost part of their weight, and the water would have gained it. Sometimes, however, it is an extremely small portion of a substance which is soluble, but it is that in which its most remarkable qualities reside. Thus a small piece of spice will communicate a strong flavour to a large quantity of liquid, with very little loss of weight.

Pup. Will all liquors dissolve the same things?

Tut. By no means. Many dissolve in water that will not in spirit of wine; and the contrary. And upon this difference many curious matters in the arts are founded. Thus, spirit-varnish is made of a solution of various gums or resins in spirits that will not dissolve in water. Therefore, when it has been laid over any surface with a brush, and is become dry, the rain or moisture of the air will not affect it. This is the case with the beautiful varnish laid upon coaches. On the other hand, the varnish left by gum-water could not be washed off by spirits.

Pup. I remember when I made gum-water, upon setting the cup in a warm place, it all dried away, and left the gum just as it was before. Would the same happen if I had sugar or salt dissolved in water?

Tut. Yes, upon exposing the solution to warmth, it would dry away, and you would get back your salt and sugar in a solid state as before.

Pup. But if I were to do so with a cup of tea, what should I get?

Tut. Not tea-leaves, certainly! But your question requires a little previous explanation. It is the property of heat to make most things fly off in vapour, which is called evaporation, or exhalation. But this it does in very different degrees to different substances. Some are very easily made to evaporate; others very difficultly; and others not at all by the most violent fire we can raise. Fluids in general are easily evaporable; but not equally so. Spirit of wine flies off in vapour much sooner than water; so that if you had a mixture of the two, by applying a gentle heat you might drive off almost all the spirit, while the greater part of the water would remain. Water, again, is more evaporable than oil. Some solid substances are much disposed to evaporate: thus, smelling salts may by a little heat be entirely driven away in the air. But in general, solids are more fixed than fluids; and, therefore, when a solid is dissolved in a fluid, it may commonly be recovered again by evaporation. By this operation common salt is got from seawater and salt springs, both artificially, and, in hot countries, by the natural heat of the sun. When the water is no more than is just sufficient to dissolve the salt, it is called a saturated solution, and on evaporating the water further, the salt begins to separate, forming little regular masses called crystals. Sugar may be made in like manner to form crystals, and then it is sugar-candy.

Pup. But what is a sirup?

Tut. That is when so much sugar is dissolved as sensibly to thicken the liquor, but not to separate from it. Well—now to your question about tea. On exposing it to considerable heat, those fine particles in which its flavour consists, being as volatile or evaporable as the water, would fly off along with it; and when the liquor came to dryness, there would be left only those particles in which its roughness and colour consist. This would make what is called an extract of a plant.

Pup. What becomes of the water that evaporates?

Tut. It ascends into the air, and unites with it. But if in its way it be stopped by any cold body, it is condensed, that is, it returns to the state of water again. Lift up the lid of the teapot and you will find water collected on the inside of it, which is condensed steam from the hot tea beneath. Hold a spoon or knife in the way of the steam which bursts out of the spout of the teakettle, and you will find it immediately covered with drops. This operation of turning a fluid into vapour, and then condensing it, is called distillation. For this purpose, the vessel in which the liquor is heated is closely covered with another called the head, into which the steam rises and is condensed. It is then drawn off by means of a pipe into another vessel called the receiver. In this way all sweet-scented and aromatic liquors are drawn from fragrant vegetables, by means of water or spirits. The fragrant part being very volatile rises along with the steam of the water or spirit, and remains united with it after it is condensed. Rosewater, and spirits of lavender, are liquors of this kind.

Pup. Then the water collected on the inside of the teapot-lid should have the fragrance of the tea.

Tut. It should—but unless the tea were fine, you could scarcely perceive it.

Pup. I think I have heard of making salt water fresh by distilling.

Tut. Yes. That is an old discovery lately revived. The salt in seawater, being of a fixed nature, does not rise with the steam; and therefore, on condensing the steam, the water is found to be fresh. And this indeed is the method nature employs in raising water by exhalation from the ocean, which, collecting in clouds, is condensed in the cold region of the air, and falls down in rain.

But our tea is done: so we will now put an end to our chymical lecture.

Pup. But is this real chymistry?

Tut. Yes, it is.

Pup. Why, I understand it all without any difficulty.

Tut. I intended you should.