Part 25 (1/2)

846. The equivalent numbers do not profess to be exact, and are taken almost entirely from the chemical results of other philosophers in whom I could repose more confidence, as to these points, than in myself.

847. TABLE OF IONS.

_Anions_.

Oxygen 8 Chlorine 35.5 Iodine 126 Bromine 78.3 Fluorine 18.7 Cyanogen 26 Sulphuric acid 40 Selenic acid 64 Nitric acid 54 Chloric acid 75.5 Phosphoric acid 35.7 Carbonic acid 22 Boracic acid 24 Acetic acid 51 Tartaric acid 66 Citric acid 58 Oxalic acid 36 Sulphur (?) 16 Selenium (?) Salpho-cyanogen

_Cations_.

Hydrogen 1 Pota.s.sium 39.2 Sodium 23.3 Lithium 10 Barium 68.7 Strontium 43.8 Calcium 20.5 Magnesium 12.7 Manganese 27.7 Zinc 32.5 Tin 57.9 Lead 103.5 Iron 28 Copper 31.6 Cadmium 55.8 Cerium 46 Cobalt 29.5 Nickel 29.5 Antimony 61.67 Bis.m.u.th 71 Mercury 200 Silver 108 Platina 98.6?

Gold (?)

Ammonia 17 Pota.s.sa 47.2 Soda 31.3 Lithia 18 Baryta 76.7 Strontia 51.8 Lime 28.5 Magnesia 20.7 Alumina. (?) Protoxides generally.

Quinia 171.6 Cinchona 160 Morphia 290 Vegeto-alkalies generally.

848. This Table might be further arrange into groups of such substances as either act with, or replace, each other. Thus, for instance, acids and bases act in relation to each other; but they do not act in a.s.sociation with oxygen, hydrogen, or elementary substances. There is indeed little or no doubt that, when the electrical relations of the particles of matter come to be closely examined, this division must be made. The simple substances, with cyanogen, sulpho-cyanogen, and one or two other compound bodies, will probably form the first group; and the acids and bases, with such a.n.a.logous compounds as may prove to be _ions_, the second group.

Whether these will include all _ions_, or whether a third cla.s.s of more complicated results will be required, must be decided by future experiments.

849. It is _probable_ that all our present elementary bodies are _ions_, but that is not as yet certain. There are some, such as carbon, phosphorus, nitrogen, silicon, boron, alumium, the right of which to the t.i.tle of _ion_ it is desirable to decide as soon as possible. There are also many compound bodies, and amongst them alumina and silica, which it is desirable to cla.s.s immediately by unexceptionable experiments. It is also _possible_, that all combinable bodies, compound as well as simple, may enter into the cla.s.s of _ions_; but at present it does not seem to me probable. Still the experimental evidence I have is so small in proportion to what must gradually acc.u.mulate around, and bear upon, this point, that I am afraid to give a strong opinion upon it.

850. I think I cannot deceive myself in considering the doctrine of definite electro-chemical action as of the utmost importance. It touches by its facts more directly and closely than any former fact, or set of facts, have done, upon the beautiful idea, that ordinary chemical affinity is a mere consequence of the electrical attractions of the particles of different kinds of matter; and it will probably lead us to the means by which we may enlighten that which is at present so obscure, and either fully demonstrate the truth of the idea, or develope that which ought to replace it.

851. A very valuable use of electro-chemical equivalents will be to decide, in cases of doubt, what is the true chemical equivalent, or definite proportional, or atomic number of a body; for I have such conviction that the power which governs electro-decomposition and ordinary chemical attractions is the same; and such confidence in the overruling influence of those natural laws which render the former definite, as to feel no hesitation in believing that the latter must submit to them also. Such being the case, I can have, no doubt that, a.s.suming hydrogen as 1, and dismissing small fractions for the simplicity of expression, the equivalent number or atomic weight of oxygen is 8, of chlorine 36, of bromine 78.4, of lead 103.5, of tin 59, &c., notwithstanding that a very high authority doubles several of these numbers.

-- 13. _On the absolute quant.i.ty of Electricity a.s.sociated with the particles or atoms of Matter._

852. The theory of definite electrolytical or electro-chemical action appears to me to touch immediately upon the _absolute quant.i.ty_ of electricity or electric power belonging to different bodies. It is impossible, perhaps, to speak on this point without committing oneself beyond what present facts will sustain; and yet it is equally impossible, and perhaps would be impolitic, not to reason upon the subject. Although we know nothing of what an atom is, yet we cannot resist forming some idea of a small particle, which represents it to the mind; and though we are in equal, if not greater, ignorance of electricity, so as to be unable to say whether it is a particular matter or matters, or mere motion of ordinary matter, or some third kind of power or agent, yet there is an immensity of facts which justify us in believing that the atoms of matter are in some way endowed or a.s.sociated with electrical powers, to which they owe their most striking qualities, and amongst them their mutual chemical affinity.

As soon as we perceive, through the teaching of Dalton, that chemical powers are, however varied the circ.u.mstances in which they are exerted, definite for each body, we learn to estimate the relative degree of force which resides in such bodies: and when upon that knowledge comes the fact, that the electricity, which we appear to be capable of loosening from its habitation for a while, and conveying from place to place, _whilst it retains its chemical force_, can be measured out, and being so measured is found to be _as definite in its action_ as any of _those portions_ which, remaining a.s.sociated with the particles of matter, give them their _chemical relation_; we seem to have found the link which connects the proportion of that we have evolved to the proportion of that belonging to the particles in their natural state.

853. Now it is wonderful to observe how small a quant.i.ty of a compound body is decomposed by a certain portion of electricity. Let us, for instance, consider this and a few other points in relation to water. _One grain_ of water, acidulated to facilitate conduction, will require an electric current to be continued for three minutes and three quarters of time to effect its decomposition, which current must be powerful enough to retain a platina wire 1/104 of an inch in thickness[A], red-hot, in the air during the whole time; and if interrupted anywhere by charcoal points, will produce a very brilliant and constant star of light. If attention be paid to the instantaneous discharge of electricity of tension, as ill.u.s.trated in the beautiful experiments of Mr. Wheatstone[B], and to what I have said elsewhere on the relation of common and voltaic electricity (371. 375.), it will not be too much to say that this necessary quant.i.ty of electricity is equal to a very powerful flash of lightning. Yet we have it under perfect command; can evolve, direct, and employ it at pleasure; and when it has performed its full work of electrolyzation, it has only separated the elements of _a single grain of water_.

[A] I have not stated the length of wire used, because I find by experiment, as would be expected in theory, that it is indifferent.

The same quant.i.ty of electricity which, pa.s.sed in a given time, can heat an inch of platina wire of a certain diameter red-hot, can also heat a hundred, a thousand, or any length of the same wire to the same degree, provided the cooling circ.u.mstances are the same for every part in all cases. This I have proved by the volta-electrometer. I found that whether half an inch or eight inches were retained at one constant temperature of dull redness, equal quant.i.ties of water were decomposed in equal times. When the half-inch was used, only the centre portion of wire was ignited. A fine wire may even be used as a rough but ready regulator of a voltaic current; for if it be made part of the circuit, and the larger wires communicating with it be s.h.i.+fted nearer to or further apart, so as to keep the portion of wire in the circuit sensibly at the same temperature, the current pa.s.sing through it will be nearly uniform.

[B] Literary Gazette, 1833, March 1 and 8. Philosophical Magazine, 1833, p. 201. L'Inst.i.tut, 1833, p.261.

854. On the other hand, the relation between the conduction of the electricity and the decomposition of the water is so close, that one cannot take place without the other. If the water is altered only in that small degree which consists in its having the solid instead of the fluid state, the conduction is stopped, and the decomposition is stopped with it.

Whether the conduction be considered as depending upon the decomposition, or not (443. 703.), still the relation of the two functions is equally intimate and inseparable.

855. Considering this close and twofold relation, namely, that without decomposition transmission of electricity does not occur; and, that for a given definite quant.i.ty of electricity pa.s.sed, an equally definite and constant quant.i.ty of water or other matter is decomposed; considering also that the agent, which is electricity, is simply employed in overcoming electrical powers in the body subjected to its action; it seems a probable, and almost a natural consequence, that the quant.i.ty which pa.s.ses is the _equivalent_ of, and therefore equal to, that of the particles separated; i.e. that if the electrical power which holds the elements of a grain of water in combination, or which makes a grain of oxygen and hydrogen in the right proportions unite into water when they are made to combine, could be thrown into the condition of _a current_, it would exactly equal the current required for the separation of that grain of water into its elements again.

856. This view of the subject gives an almost overwhelming idea of the extraordinary quant.i.ty or degree of electric power which naturally belongs to the particles of matter; but it is not inconsistent in the slightest degree with the facts which can be brought to bear on this point. To ill.u.s.trate this I must say a few words on the voltaic pile[A].

[A] By the term voltaic pile, I mean such apparatus or arrangement of metals as up to this time have been called so, and which contain water, brine, acids, or other aqueous solutions or decomposable substances (476.), between their plates. Other kinds of electric apparatus may be hereafter invented, and I hope to construct some not belonging to the cla.s.s of instruments discovered by Volta.