CHAPTER V.

CHEMICAL ACTION.

DEFINITION OF CHEMICAL ACTION—HEAT-ATMOSPHERIC TEMPERATURE-CHEMICAL AFFINITY-DIVINE AGENCY IN CHEMICAL CHANGES -LAWS OF CHEMICAL COMBINATION-CHEMICAL BEHAVIOUR OF OXYGEN, OF NITROGEN, OF HYDROGEN, OF CHLORINE, OF CARBONIC ACID, OF WATER, AND OF OTHER SUBSTANCES-CHEMICAL TRANSMUTATIONS OF COLOUR-NATURAL FIELDS OF FIRE" AND BURNING SPRINGS IGNIS FATUUS-PHOSPHORESCENCE.

WHATEVER turns two or more substances into one of a different nature, or so alters one substance as to give it a new set of properties, is called chemical action. Two things which have a good deal to do with it are light and electricity; and a third is heat. These three things, indeed, as we have already hinted, are very intimately connected with one another, and possibly may be found, in the future progress of discovery, to be only different conditions or different emanations of some extremely subtle primal power which effects and controls all sorts of changes among the particles of

matter.

Heat is evolved in a primary or originating way from the sun's rays, and from electric action; and in a secondary or liberating way from burning, striking, rubbing, and some kinds of mixing. It is usually imagined to consist of molecules which repel one another, and are attracted by all other substances. It

always increases the bulk, but never the weight, of the things which it enters; yet expands different kinds of things, and different conditions of the same thing, in widely different degrees. An augmentation of it, more or less, in most known solids, converts them into liquids,—and in liquids, converts them into gases; and vice versa, the withdrawal of it, more or less, from most known gases, converts them into liquids,—and from liquids, converts them into solids. It is, therefore, the grand agent, whatever else may be a means, in all liquefactions, evaporations, and rarefactions; and conversely, or by diminution, in all condensations, congelations, freezings, and solidifications. Cold is simply the negation of heat; and what is powerful cold to one substance, as estimated by condensing or freezing effects, is mild or high heat to another.

The heat of the atmosphere, with exceptions which are trivial, and do not act steadily, is derived altogether from the sun's beams; and as these, for the most part, especially in clear climes and cloudless weather, do not divide into their component rays till they reach the ground, their heat is set free principally in the course of contact with sea and land, and particularly with herbage and earths. This is the reason why the atmosphere is warmer in the lower strata than in the higher, and in valleys than on mountains; and, together with the comparative directness or deflectedness of the line in which the beams descend in different latitudes, and at different hours, it is the reason also why the atmosphere is warmer in the torrid zone than in the temperate zones, and in three or four hours after mid-day than in the morning or in the evening. The air immediately over the ground receives all the

developed heat, and undergoes continual replacement by cooler air from above; and the ground accumulates heat by excess of the quantity which it receives over the quantity which it gives off, from sunrise till a maximum about two hours or so after noon. Hence, what is called the temperature of the atmosphereone of the grandest agents in its many magnificent wonders is simply its ever-varying perceptible heat in different latitudes, altitudes, humidities, hours, and seasons. But the comparative amount of this at any place and moment, or the degrees and fluctuations of it in general, can be ascertained only by means of regularly expansible substances, such as the alcohol and the mercury employed in thermometers, and not at all by man's sensations; for what is a cold temperature of either air or anything else to a man in one set of circumstances, is a hot one to him in another; and even the same temperature-for example, of a basin of river water-may be cold to his right hand, which he has just been holding before a fire, and hot to his left one, with which he has just been handling snow.

Heat, under certain conditions, goes so into combination with substances as to become incapable of detection by either the senses or the thermometer, and is then said to be latent. A vast quantity of it, for instance, combines with melting ice or melting snow, in order to give it the steady form of water; and a still vaster quantity combines with vapourising or with boiling water, in order to give it the steady form of vapour; and all these quantities are again let loose when respectively the vapour resolves into rain, and the water solidifies into ice. Hence the curious fact that the air is much chiller during the commencement

of a thaw than during the commencement of a frost; for, in the former case, it is losing the enormous quantities of heat which are going into combination with the melting ice or snow, while in the latter it is gaining just the same quantities which are coming out of combination with the freezing water. And, in general, whenever substances of any kind retain comparatively expanded forms with ordinary or comparatively low temperatures, they so hold quantities of heat in combination as to let not a particle of it out to any object which touches them, and then all at once let much or all of it go free under any process which suddenly reduces their bulk. Even a piece of cold metal, quite irrespective of the heat which it can take in and give out in rises and falls of temperature, possesses so large an amount of latent heat as to set free a perceptible quantity at every stroke of a hammer. And when equal measures of cold water and cold oil of vitriol are suddenly mixed, they jointly assume not a very great deal less bulk than the two measures, and yet develop so much heat as to set the mixture a-boiling.

The force which effects chemical action between two or more elements or substances, so as to transmute them into another substance with other properties, is called chemical affinity. But whether this be sometimes almost identical with heat, sometimes almost identical with electricity, sometimes almost identical with light, or always a primal power comprising all the three, or always a peculiar force different from them all, and only using them as means, or even a correlation between some pervading force over all things, and a various capacity in things themselves to

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accept its action, no mortal can tell. Be it what it may, it governs inanimate substances as mightily as life governs animated beings, and also according to as fixed and manifest laws, and also as wondrously, as wisely, as benignantly, and as mysteriously; so that, in the true, calm, ultimate view of chemical affinity, as in the true, calm, ultimate view of life, we must simply pronounce it the expression or working of the will of God.

Some substances have no observed affinity for one another, or have never been known to combine; some have but a chary affinity for one another, or combine only in extraordinary circumstances; and some have a very keen affinity for one another, or leap into combination wherever and however they meet. One can combine with only a few others; another can combine with multitudes; and almost every one has such a scale of likings, that it comes out of a first substance in order to go into a second, and out of a second in order to go into a third. Some things, as in the rusting of iron and in the decay of timber, combine slowly, and without any display; and other things, as in the burning of oil and in the exploding of gunpowder, combine rapidly or instantaneously, and with grand appeals to the senses. Some combinations look like annihilations, converting solid substances into imperceptible gases; others look like creations, converting imperceptible gases into liquids or powders; and multitudes look like deeds of magic, totally changing consistencies, forms, colours, odours, sapidities, and all other classes of observable properties. Hundreds of these magnificent changes go on in the common proeesses of kitchens and factories, and fail to be universally striking solely on account of being universally