CHAPTER XXXVII.

[Verse: "Where wast thou when I laid the foundations of the earth? declare, if thou hast understanding."]

792. _What is repulsion?_

Repulsion is that property in matter by which it _repels_ or _recedes from_, those bodies for which it has _no attraction or affinity_.

793. _Why does dew form into round drops upon the leaves of plants?_

Because it _repels the air_, and the _substances of the leaves_ upon which it rests. Because, also, its own particles _cohere_.

794. _Why do drops of water roll over dusty surfaces?_

Because they _repel_ the particles of dust; and also because their own particles have _a stronger attraction for each other_ than for the particles of dust.

795. _Why does a needle float when carefully laid upon the surface of water?_

Because the needle and the water _mutually repel each other_.

796. _Why does water, when dropped upon hot iron, move about in agitated globules?_

Because the _caloric_ repels the particles of the water.

797. _Why does oil float upon the surface of water?_

Because, besides being specially lighter than water, the particles of the oil and the water _mutually repel each other_.

798. _What is carbonic acid?_

Carbonic acid is a mixture of _carbon_ and _oxygen_, in the proportion of 3 lbs. of carbon to 8 lbs. of oxygen.

[Verse: "Who hath laid the measures thereof, if thou knowest? or who hath stretched the line upon it?"]

799. _Where does carbonic acid chiefly exist?_

It exists in various natural bodies in which carbon and oxygen are combined; it is evolved by the decomposition of numerous bodies called carbonates, in which carbon is united with a particular base, such as the carbonate of lime, the carbonate of iron, the carbonate of copper, &c. It is also evolved by the processes of _fermentation_, by the _breathing of animals_, the _combustion of fuel_, and the _functions of plants_. Carbonic acid also _exists in various waters_.

Carbonic acid is _found most largely in solid combinations with other bodies_: it forms 44-100ths of all limestones and marbles, and it exists in smaller quantity, combined with other earths, and with metallic oxides.

800. _What are the states in which pure carbonic acid exists?_

Pure carbonic acid may exist in the _solid_, the _liquid_, or the _æriform_ state. In the _solid state_ it is produced only by artificial means, and it is then a white crystallised body, in appearance _like snow_; in the _liquid state_ it is a _heavy colourless fluid_; in the _æriform state_ it is a _pungent_, _heavy_, _colourless gas_, and is known as _carbonic acid gas_.

801. _Why does bottled porter produce large volumes of froth, much more than the bottle could contain?_

Because, by the fermentive process, _carbonic acid_ has been developed in the porter, and is held in _liquid solution_; but it always has a _strong tendency to escape_, and directly the pressure is removed, it _evolves into gas_, by which it occupies much greater space, and forces the porter in millions of small bubbles out of the bottle.

802. _Why does soda-water effervesce?_

Because _carbonic acid gas_ is forced into the water _by pressure_. Pressure _alters the gas into a liquid_, and directly the pressure ceases, the liquid again _evolves into gas_.

803. _Why does spring water taste fresh and invigorating?_

Because it contains _carbonic acid_.

[Verse: "Whereupon are the foundations thereof fastened? or who laid the cornerstone thereof."--JOB XXXVIII.]

804. _Why does boiled water taste flat and insipid?_

Because the _carbonic acid_ has been _driven off_ by boiling.

805. _Why does beer which has been standing in a glass taste flat?_

Because its _carbonic acid_ has escaped as _carbonic acid gas_.

806. _Why, when we look into a glass of champagne, do we see bubbles spontaneously appear at the bottom, and then rise to the top?_

Because, in the places where the bubbles are formed, the _liquid carbonic acid_ is evolving into _carbonic acid gas_.

807. _Why do the bubbles arise from two or three points in columns, rapidly succeeding each other?_

Because, when the formation of gas once begins, and bubbles ascend, there is _less pressure_ in the line of the _column of bubbles_; the carbonic acid, therefore, draws towards those points as the _easiest channel of escape_.

These explanations equally apply to the "working" of beer, by which yeast is produced; to the effervescence of various waters, acidulated drinks, ginger beer, &c., and also to the "sponging" of bread, &c.

808. _Why does gunpowder explode?_

Gunpowder is made of a very intimate _mechanical mixture_ of _nitrate of potash_, _charcoal_, and _sulphur_. When these substances are heated to a certain degree, the nitrate of potash is decomposed, and its _oxygen_ combines with the _charcoal_ and _sulphur_, instantaneously forming _large volumes of carbonic acid gas_ and _nitrogen_, which, seeking an escape, produce an explosion.

809. _Why does charcoal act as a powerful disinfectant?_

Because the _carbon_ readily absorbs, and combines with _various gases_, neutralising their _offensive odours_, and destroying their _unhealthy properties_.

Let us now pause for a few moments to consider the importance of those two great divisions of nature, Air and Water, and to reflect upon the wisdom of some of those laws which are connected with the phenomena thereof, and which have not yet been sufficiently explained.

[Verse: "Thus saith the Lord, Let not the wise man glory in his wisdom, neither let the mighty man glory in his might, let not the rich man glory in his riches."--JEREMIAH IX.]

We have seen that the air is a thin elastic body surrounding the globe; that it consists of certain gases essential to the life of animals, and to the growth of plants; and that it takes part in most of those chemical changes, which mark the transformations of the inorganic creation. Whether it be the burning of a piece of wood, the evaporation of a drop of water, the breathing of an animal, the respiration of a plant, or the fermentation of bodies, the air in almost every instance gives or receives--and in most of the operations in which it engages, it does both.

But there is one point of view, which we must add to those which have already been considered: the order of nature consists of generation, life, and death. Every beat of the watch signals the birth of millions of living things, and the same beat proclaims that as many living organisms have yielded up their vital spark, and that forthwith the elements of which they are composed must be dissolved, and restored to the great laboratory of nature.

The air is the vast receptacle of those organic matters which are undergoing dissolution. The body of the shipwrecked mariner, cast upon the shore of a desolate island, blackens in the sun, and the full round form gradually dwindles to skin and bone, until at last the few atoms that remain crumble into dust, and are scattered to the wind. The same process occurs, with some modifications, whether bodies are buried in the earth, or dissolve upon its surface. The leaves of forests fall and accumulate in heaps, where they ferment and dissolve, leaving only their more earthy particles behind.

The amount of matter which day by day passes from the state of the living to that of the dead, must be enormous; but from the difficulties of acquiring data, beyond the possibility of calculation. Such statistics as we have, however, enable us to form conclusions as to the mighty agencies in which the air is constantly engaged. There are on the earth 1,000,000,000 inhabitants of whom nearly 35,000,000 die every year, 91,824 every day, 3,730 every hour, and 60 every minute. But _even the living die daily_, and undergo an invisible change of substance, as we shall hereafter explain.

The bodies of those many millions are dissolved in the air, in vapours and gases which, before the dissolution of each corporeal organism is complete, begin to live again in the various forms of vegetable and animal life.

Of the number of animals living and dying upon the face of the earth, we can form no adequate estimate. Of mammals there are about 2,000 ascertained species; of birds 8,000 species; of reptiles 2,000 species; of fishes some 8,000 or 10,000 species; of molluscs some 15,000 species; of shell fish 8,000 species; of insects 70,000 species. And, including others not specified here, the total number of _species_ of animals probably amounts to no less than 250,000,--each species consisting of _many millions_ of living creatures.

In the area of London alone, no less than 200,000 tons of fuel are annually cast into the air in the form of smoke. And if we take into account the vast operations of nature in evaporation, fermentation, and putrefactive decomposition, we may be enabled to form a conception of the mighty part which that _thin air_, of which we think so little, plays in the grand alchemy of nature.

[Verse: "I will praise thee; for I am fearfully and wonderfully made; marvellous are thy works; and that my soul knoweth right well."--PSALM CXXXIX.]

In addition, also, to the facts already communicated, respecting the sound-bearing and light-refracting properties of air, it must be remarked, that but for the atmosphere, and the general refraction of light by its particles--each atom as it were catching a fairy taper, and dancing with it before our view--the condition of vision would be widely opposite to that which exists, and totally unsuited to our wants. The various objects upon which the illuminating rays of the sun fell, would be lighted up with an intense glare, but all around would be darkness, just as when a single ray of light is passed into a dark chamber, and directed upon a solitary object. The air, without becoming itself visible, _diffuses luminous rays_, in modified intensity, in every direction. If the air reflected so much light as to render _itself visible_, it would appear like the glittering surface of the water reflecting the solar rays, and we should then be unable to see the various objects which surround us.

Of the importance of Water in the scheme of creation, man generally entertains an imperfect conception. It is simply supposed to afford moisture to plants, drink to animals, and to promote salubrity by its cleansing properties. Let us, however, contemplate man as he stands before us, noble in form, erect in position, full of strength, joy, ambition. How much of that noble form is composed of water? Suppose that it could all be instantaneously withdrawn--not the oxygen and the hydrogen, which might combine to form water--but the fluid that exists in his body as _water_, unchanged--except by mechanical admixture with the secretions of the body--Why then that beautiful temple would collapse and become a mere shred, so thin, that it would seem but a shadow of the body as it existed before, and the beholder might doubt whether life ever inhabited a frame whose structure was so frail. It is said that _three-fourths_ by weight of the human body consist of _water_. Thus, if man weighs 120lbs., 90lbs. consist of water, and this subtracted, only 30lbs. of solid matter remain. This statement is rather under than over the fact.

The assertion is startling, but so true that it can be verified by simple experiment. A piece of lean flesh--say of beef--cut an inch thick, and placed in a slow oven, and allowed to remain until all its water was driven off in vapour, would become as thin as a wafer, and as light as a cork. With a more scientific arrangement, it would be possible to collect the water, and the weights of the condensed vapour, and of the solid residue, would together make up the weight of the beef: if the piece weighed sixteen ounces, the weight of the water would be about 14 ounces, and the _solid matter_ about _two ounces_.

Water holds a similar proportion in the bodies of all animals, and of vegetables. It is evident, therefore, that it occupies a more important place in the scale of creation than is generally accorded to it by the unobservant mind. We are indebted to it for those atmospheric changes which constitute the peculiar feature of our varying climate. Rising in invisible vapours, it builds palaces of glory in the skies, and often presents to the view of man the imagery of heaven. Persons who have ascended above the altitude of the clouds, have described the scene upon looking down towards them as the most celestial that the mind can conceive. Fields of fleecy radiance, majestically rolling like a sea of gold, occupied the whole range of vision, and seemed to embellish an eternity of space. Those golden clouds that at one time are decked in the richest splendour, and occupy the upper chambers of the Court of Nature, become grave councillors when the earth grows thirsty, and the plant droops with languor. They roll their heavy brows together, as in consultation upon some grave necessity: down come the refreshing showers, the mighty tongue of thunder rocks the air, the earth is drenched, and becomes fresh with the salubrity of her toilette; obnoxious substances, with their offensive exhalations, are swept away: living things rejoice, and beautiful flowers throw their incense in thanksgiving into the air; the broad blue heavens for a time look down and smile upon the blessed work; and then the clouds again gather in a golden train, and one by one fill the high arches of the atmosphere, until the earth once more grows thirsty, and the flower supplicates for drink.

[Verse: "How mighty are his wonders! his kingdom is an everlasting kingdom, and his dominion is from generation to generation."--DANIEL IV.]

With reference to Light, its wonders, and the curious but imperfect theories respecting it, we have little to add, except with regard to its physiological action upon the eyes of man and of animals, which will be given in another place. But of its sister, Darkness--for it would not do now to call darkness the antagonist of light, since it will be seen that they work harmoniously for good--we have to say, that recent discoveries indicate that darkness is as necessary to the health of nature as light. Not only is it necessary to compose man and animals to sleep, to give rest to the over-wrought nerves of the industrious--but light is the quickening power of vegetation, and although plants grow by night, they grow, as man does, when stretched upon his bed--but some of their functions, which are actively excited in the presence of light, are at rest in darkness. Nor is this all: there is not an atom upon the face of the earth which is not affected by the rays of the sun, their light, their heat, their actinism. Colours change: some are bleached, others are darkened. All bodies are expanded. The hardest rock sustains _an effect_ from the sun's rays; and an unceasing sun, shining upon the hardest granite, would in time produce such a disturbance of its atomic condition, that adamant would crumble away to dust.

The going down of the sun, therefore, marks the period when not only does the bird fly to her resting-place, and man turn to his couch; but when _every atom of a vast hemisphere_ subsides into a state of quietude, and when homogeneous particles of matter return to their mutual rest.

In a few succeeding lessons, we intend to point out some of the scientific truths that are _illustrated in the use of toys_. We think we shall be able to show to our young readers, that even the hours of play may be made the periods of delightful instruction; and that there is _no_ "reason why" the acquirement of knowledge should not sweetly accord with the occasional pursuit of those pastimes by which health of body and vigour of mind are induced.

But before we commence the discharge of that pleasant duty, let us say a few words respecting Carbon, that important agent in the world's history. It is, doubtless, perplexing to the minds of many persons, to understand how the _diamond_ can be _pure carbon_; how _charcoal_ can be _carbon_ a _little less pure_ than the diamond; and how _coal_ and _sugar_ can also be carbon, _less pure_ than the charcoal. The statement that in the diamond carbon exists in a different atomic condition, is almost as instructive to the inquiring mind, as to say, "It is so, _because it is_."

Diamonds are expensive things, and so difficult to experiment upon, even if they were not expensive, that the doors of inquiry seem locked. To turn diamonds into charcoal, or into carbonic acid gas, is a very costly formula of experiment. Charcoal fires, thus sustained, would soon burn a man out of his house; and soda water, impregnated with carbonic acid gas, produced from diamonds, would be a very expensive beverage. If we could only turn charcoal into diamonds, and carbonic acid gas into brilliants, that would be quite another affair. A new Eldorado would be discovered, and there would be so many experimenters that, when they all succeeded, they would find that diamonds had lost their value. However, as a fact for the encouragement of those who would like to be early in the race, we may state that the atoms of charcoal which are repulsed from the charcoal points, during the electric agitation which produces the electric light, acquire a hardness and a sharpness almost equal to that of the diamond--only there is still the awkward obstacle in the way, that _they happen to be black_.

[Verse: "He delivereth and rescueth, and he worketh signs and wonders in heaven and in earth."--DANIEL VII.]

We must see, therefore, whether there is anything in nature that we can experiment upon, theoretically or practically, to give us a clearer conception of this difficult matter. There is a large _dew-drop_ resting upon a luxuriant cabbage leaf--one of those great leaves that have flourished in defiance of the snail, and now spreads out like the gigantic frond of the _Victoria Regina_. That dew-drop is one of the beautiful diamonds which Nature sprinkles about on cloudless nights, as if to show the stars, in answer to their twinkling, that we have something that will glisten and twinkle too.

The dew-drop is a very good imitation of a diamond, and to the lover of God's works, quite as precious as the stone set in gold. It does not consist of carbon--it probably may have a mite of carbonic acid in its embrace--but that is not necessary to our purpose: all we want to know is, _the different atomic conditions_ of which bodies are susceptible, and the very dissimilar appearances they exhibit under the variations of atomic states. It doesn't glisten so much as the diamond, _because it is round_--if we could cut it into a number of _facets_, it would refract light almost as perfectly as the diamond. It is not _solid_--but we can freeze it, and we shall at once exhibit two different atomic conditions, that will represent nearly enough the diamond, and the liquid carbonic acid. Then, if we evaporate the dew-drop, we shall produce a volume of vapour nearly _two thousand times as large as the dew-drop_. The steam will be white; but we have only to imagine it black, and then we get an analogy of the differences of the atomic conditions that prevail in _the diamond_, _carbonic acid_, and _charcoal_, _tinder_, _lamp-black_, or any light form of carbon. Of course we have been illustrating _atomic conditions only_, and not chemical composition.

There are a few other facts connected with carbon that merit consideration. Carbonic acid gas, _entering the lungs_, is a _deadly poison_; but _entering the stomach_, which lies close under the lungs, and is over-lapped by them, it is a _refreshing beverage_. Although charcoal, when burnt, gives off the most poisonous gas, it seems to be very jealous of other gaseous poisons; for if it be powdered, and set about in pans where there is a poisonous atmosphere, it will seize hold of poisonous gases, and, by absorbing, imprison them. Even in a drop of toast and water, the charred bread seizes hold of whatever impurities exist in the water; and water passed through beds of charcoal, becomes filtered, and made beautifully pure, being compelled to give up to the charcoal whatever is obnoxious. If a piece of meat that has already commenced putrifying, be sprinkled with charcoal, it will not only object to the meat putrifying any further, but it will _sweeten that which has already undergone putrefaction_. Although, in the form of gas, it will poison the blood, and cause speedy stupefaction and death; if it be powdered, and stitched into a piece of silk, and worn before the mouth as a respirator, it will say to all poisonous gases that come to the mouth with the air, "I have taken this post to defend the lungs, and I arrest you, on a charge of murderous intention." Such are the various facts connected with carbon; and they forcibly indicate that those who understand Nature's works, are likely to receive her best protection.

[Verse: "The father of the righteous shall greatly rejoice; and he that begetteth a wise child shall have joy of him."--PROVERBS XXIII.]