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9. What length of thread did 23 grains 16. Are not millions of insects found in ot suk make?
a single drop of liquid ? 10. Explain to ine how one grain of gold 17. Must noi parts of these creatures be may be divided into 5761 visible parts. inconceivably sınalı?
11. Give me further instances of the 18. Tell me about the piece of sugar in manner in which gold can be divided, par- the tea, the drop of wine in the tumbler ticularly in its covering silver wire and of water, the grain of copper in the nitric gilding buttons.
acid. 12. Are not the natural divisions of 19. What do you understand by ultimatter much more wonderful than the mate particles ? artiticial?
20, Explain to me the difference be13. What about the grain of musk in a tween mutter and body. room?
21. Is not the earth where we live teeni14. Before we can smell a body, must ing with wonders ? somne portions of the substance touch the 22. Must not the great Being who made, nostruls ?
supports, and governs all things, be 15. What does the dust of the Lycoper- worthy of all love and praise ? dun turn out to be under the inicroscope?
II.- A CHEMICAL TEA LECTURE.
.... vapor. Op-er-a'tion, n
.... halāre. In-fu'sion, n...............funděre. Sat'u-ra-ted, adj......... satis. Ex'tract, n....
.trahěre. Vola-tile, adj... .. volāre.
chem'is-try, n. Dis-persed', part.... .spargěre.
weighed, part. Dis-solves', v... ..solvěre.
mois'ture, n. Solvent n..... ..solvere,
fla'vour, n. Tur'bid, adj. ... turba.
Tutor. Come: the tea is ready. Lay by your book, and let us talk a little. You have often assisted in making tea, but perhaps have never considered what kind of an operation it is.
Pupil. An operation of cookery, is it not?
T. You may call it so; but it is properly an operation of chemistry.
P. Of chemistry! I thought that that had been a very deep sort of a business.
T. O there are many things in common life that belong to the deepest of sciences. Making tea is the chemical 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 and flavour.
P. Would not cold water do the same?
T. 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 the goodness from it as completely as possible. The greater heat and agitation of boiling makes the water act more powerfully. The liquor in which a substance has been boiled is called a decoction of that substance.
P. Then we had a decoction of mutton at dinner to-day.
T. We had_broth is a decoction, and gruel and barleywater are decoctions.
P. And ink
T. No-the materials of which ink is composed are steeped in a cold liquor, which operation is termed maceration. 'In all these cases, you see, the whole substance does not mix with the liquor, but only part of it. The reason of which is, that part of it is soluble in the liquor, and part not.
P. What do you mean by soluble ?
T. 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, the tea remaining as clear as before, though I can tell by the taste that the sugar is dispersed through all parts of it. The body which thus disappears, is said to be soluble, and the liquor it dissolves in, is called the solvent, or menstruum.
P. Salt is a soluble substance.
T. Yes. But what if I were to throw a lump of chalk into some water?
P. It would make the water white.
T. While you stirred it—no longer; afterwards it would sink undissolved to the bottom.
P. Chalk, then, is not soluble.
T. No, not in water; when stirred up in a liquor so as to cause it to lose its transparency, it is said to be diffused. 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?
P. The sugar and salt would disappear, being dissolved. The tea-leaves would yield their colour and taste. And the chalk—
T. The chalk would sink to the bottom with the tea-leaves, unless the water were stirred, when it would be rendered tur. bid or muddy. After the operation, the tea-leaves, if dried and weighed, would be found to have lost part of their weight, and the water would have gained it. In some cases, it is an extremely small portion of a substance that is soluble, but then 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, and yet lose but a trifle of its weight.
P. When I observed that chalk was insoluble, you said pointedly, in water it is: I suppose, then, that in some other liquid it is soluble.
T. Yes—in acids; that is, in vinegar and other liquids of a similar class. Indeed, in proper menstrua, not only is chalk soluble, but most other bodies ; even the metals, those solid and seemingly indestructible bodies, by being put into certain liquids, become converted into transparent fluids.
P. How exceedingly curious !
T. It is. Upon this principle are founded many curious matters in the arts. 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 substance with a brush, and is become dry, the rain or the 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.
P. I remember, when I made gum-water, upon setting the
cup in a warm place, the water all dried away, and left the gum just as it was before. Would the same happen if I had sugar or salt dissolved in the water.
T. Yes, upon exposing the solution to warmth, it would dry away,
your sugar solid state, as before.
P. But if I were to do so with a cup of tea, what should I get?
T. Not tea-leaves, certainly! But your question makes a few observations necessary. 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 easily made to evaporate; others very difficultly, and others not at all by the most violent fire we 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 by a little heat may entirely be 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. It is by this operation that common salt is obtained from sea-water and salt-springs, either by the artificial application of heat, or by the natural heat of the sun. When a quantity of water contains as much salt as it will dissolve, it is called a saturated solution ; upon evaporating which a little, the salt begins to assume the solid state, forming little regular masses called crystals. Sugar may be made in like manner to form crystals, and then it is sugar-candy. But, 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 infusion 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.
P. What becomes of the water that evaporates ?
T. A very proper question-it ascends into the air, and unites with it, causing it to become moist or dewy. however, the vapour in its way happen to 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 tea-pot, and you will see water collected on the inside of it, which is the condensed steam which rises from the hot tea beneath it. Hold a spoon or knife in the way of the steam which bursts out from the spout of the tea-kettle, and you will find it immediately covered with drops of water. This operation of turning a liquid 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 from this vessel called a still, into another called a 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. Rose-water and spirit of lavender are liquors of this kind.
P. Then the water collected on the inside of the tea-pot lid should have the fragrance of the tea.
T. It should-but unless the tea were extremely strong, you could scarcely perceive it.
P. I think I have heard of making salt water fresh by means of distillation.
T. Yes, that is an old discovery lately revived. The salt in sea-water 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 regions of the air, and falls down in rain.-But our tea is done ; so we will now put an end to our chemical lecture.
P. But is this real chemistry? T. Yes, it is. P. Why, I understand it all without any difficulty. T. I intended that you should. Evenings at Home. 1. What mean you by an infusion ? 10. How do you obtain common salt 2. What by a decoction ? 3. What by maceration?
11. If vapour be stopped by any cold 4. What do you say of a solid, when it body, what effect follows ? entirely disappears in a fluid ?
12. Explain to me the process of dis. 5. When do you say a substance is dif- tillation.
13. Whence comes the vapour that 6. Is chalk soluble in acids ?
forms clouds and rain ? 7. To what class of liquids does vinegar 14. If from the sea, why is it not salt belong?
then ? 8. What effect has heat upon most 15. Is not this arrangement of God very things, particularly liquids ?
simple looking indeed? 9. If you apply heat to a mixture of 16. But does not this very simplicity spirit-of-wine and water, which of these add to its beauty ? flies off first?
froin sea water?
III.-TRANSLATION OF THE AUTHORIZED ENGLISH
s latus, see,
Scrip'tures, n..............scriběre. ferri. In-spi-ra'tion, N............
..spirāre. Pro-found', adj.... .fundus. In-fàl-li-bil'i-ty, n........fallěre. O-rigʻi-nal, adj. ..oriri. Con-cur'rent, adj........currěre. Mar'gin-al, adj.
.margo. In-du'bi-ta-bly, adv.....dubitāre. Com-mit'tee, n..
..mittére. Ven'er-a-ble-ness, n..... Venerāri. Pro-pi'tious, adj.. .propitius. Con-sum-ma'tion, n..... summus. De-lib-er-a'tion, n..........