ary temperatures and pressures; bromine, a fluid; and iodine, a solid; in this manner displaying a progression in the difference of cohesive force. Again, chlorine is yellow; bromine, red; iodine, black, or, in vapour, a reddish violet." In the higher chemistry of organized bodies we meet with another kind of organic groups; "these are named Organic Types, the meaning of which is, that the atoms are grouped together in a certain mode, on which the properties or the compound so entirely depend, that provided this grouping or arrangement be retained, great changes may be made in regard to individual elements, without changing the general character of the compound. This leads us to the very remarkable and important law of substitution, which has become so fertile in discoveries of late years." In organic chemistry every compound represents a type, and all chemical changes are substitutions, but only like for like can be substituted, one metal for another, or chlorine for iodine, &c. In organic chemistry, the arrangement of the atoms determines the character of the type. A certain arrangement gives acids, another ethers, and so on. As an example of such an organic type, Dr. Gregory gives the case of Naphthaline C,, H., the character of which is that it is volatile and combustible. Now the hydrogen in this compound may be replaced, atom by atom, by chlorine, yielding a compound C2, Cl,, which still retains the general characters of the type. 20 20 But there is another form of substitution giving rise to homologous series, in which hydrogen is replaced by certain compound radicals which are themselves homologous and give origin, when substituted for hydrogen, to other *Faraday's Lectures on Non-Metallic Elements, pp. 158, 159. Taking methyle, the first in the series, we can see the simple relation which exists between it and all the members of the series. The second, ethyle, is derived from the first by adding two atoms of carbon, and two of hydrogen. The third bears a like relation to the second, and so on throughout. The carbon equivalents form an even number, those of the hydrogen are odd numbers. It is farther worthy of notice, that the volatility of each is inversely as the amount of carbon and hydrogen, and, consequently, the density is in direct proportion to the amount of carbon and hydrogen. The density and boiling point increase from the top to the bottom of the scale, in the order in which they stand in the above table. Methyle is a gas like hydrogen, requiring twenty atmospheres to reduce it to a fluid state, amyle is an oily fluid boiling at 311° Fahr. The radicles in the first part of the table are all homologous with, and analogous to, hydrogen. And as hydrogen, H, was the starting point in the series of radicles, (Ethyles,) so water HO is the starting-point of a new homologous series formed from these radicles, forming ethers, as represented in the second series in the table. The first of these, oxide of methyle, C, H, O, is a gas at ordinary temperatures, the others are liquids less volatile than ether, and so on. From this second series a third homologous series is 3 formed, viz., the alcohols, by the addition of two equivalents of water; one example may suffice: C, H, 0, HO give methylic alcohol, &c. It may be observed that these series, ethers and alcohols, are also analogous as well as homologous, that is, their general characters are the same. "We can now see," says Dr. Gregory, "that the progress of science must inevitably reduce the whole of organic chemistry, in which we must remember only the same three or four elements are perpetually met with, to a collection of homologous series, in which every compound will have its natural place, indicative at once of its origin, its immediate derivation, and its properties both physical and chemical.”* It is not necessary to maintain that all the laws referred to in this section, or in any of the sections, are simple and original; it is not necessary that we should regard any one of them as being so. We are at liberty to suppose that the very law of gravitation itself is derived from a simpler law, as is maintained by some in our day; still the order in the derivative law would be a proof of order in the original law itself, and in the arrangements made in order to its operations; thus, upon the discovery of the law of gravitation, the laws of Kepler were accounted for, but by a law orderly in itself, and having beautiful arrangements made in order to its beneficent action. Most of the forms of crystals found in nature are derivative, but when we go back to the original forms, we find them, like the derivative, distinguished by the most methodical symmetry. On the same principle we may argue that should the laws at present acknowledged in science be resolved into simpler ones, it would still be found that the original laws, with the * Gregory's Elementary Treatise on Chemistry, pp. 26-1, 269, 272. adjustments made in order to their operation, are of a regular and mutually adaptive character. The forms of crystals, and the relations of chemical equivalents, if not simple, must, just because they are regular, proceed from forms or from forces, one or both, which are also characterized by regularity. From disorder there can flow only confusion; order can proceed only from order. SECT. II.-ADAPTATIONS OF INORGANIC OBJECTS TO ANIMALS AND PLANTS. Many of the adjustments which might be adduced under this head are so obvious that it is not necessary to dilate on them; indeed, they can scarcely be made more impressive by any scientific treatment. While the elements of nature obey their own methodical laws, they are so arranged as to form living organisms, and supply them with the needful sustenance. Each agent has its rule of action, but is made to co-operate with every other. Law is suited to law, property fits into property, collocation is adapted to collocation, and the result is harmony and beneficence. The whole is dependent on every one of its parts, and the parts all lend their aid to the production of the whole. A break in a single thread of the complicated network would occasion the failure of the whole design. There are upwards of sixty substances, which, in our present state of knowledge, we must regard as uncompounded. Each of these has its own properties, and the system is sustained by the joint action of all. Very possibly the absence of any one of the elements, certainly the absence of any one of the thirteen more universally diffused, would throw the mundane system into confusion. Each has a purpose to serve which could be served by no other. Oxygen, so essential to animal breath and life, is the most largely distributed of them all, composing more than one half of the whole inorganic objects known to us. Hydrogen, the other element of water, no less necessary to living beings, seems to have a relation to every living organism. Carbon is a main source to us of artificial light and heat. In order that it should fulfil this end, it is necessary that it should be a solid while evolving its light and heat, (a gas has little, and this only a momentary, power of illumination); this is provided for by carbon being in itself always solid. But if the result of combustion had been also a solid, then the world would have been buried in its own ashes; this evil is avoided by the carbon going off in carbonic acid, which is volatile. The mass is all glowing one instant, the next it is dissipated into air. "Carbon," says Faraday, "possesses every quality to render it adapted to its intended uses; not one property, however seemingly unimportant, could be added or taken away without destroying the whole harmonious scheme of nature, devised with such wisdom, maintained with such care."* Each of the powers and elements of nature is in itself potent, and capable of working destructive effects, but is checked and balanced by nice adjustments. What tremendous energies does oxygen display in the phenomena of combustion, and when in the condition of ozone; yet how tranquil and passive as one of the elements of water, and as locked up in so many of the constituents of the earth's crust. The electric force held in balance in a single drop of water would, if let loose, exceed in energy the electricity of a thunder-storm. Man is placed in a state of things in which, as he is dependent, he is made every instant to feel his dependence. * Letters on Non-Metallic Elements, p. 277. |