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tube will remain full. The electric circuit is to be completed by connecting the ring s with the positive (or zinc) end of a voltaic battery, and the ring N with the negative (or copper) end, by means of two wires, one proceeding from each end; and when so completed, the decomposition of water is gradually effected: the tube A receives hydrogen gas, and the tube B oxygen gas, the former in the proportion of two to one of the latter. This experiment was performed by that scientific philanthropist, Dr. Birkbeck, before the members of the Mechanic's Institution, on the 30th March, 1825.

Voltaic troughs or batteries are sold by philosophical instrument makers; they are usually composed of alternate plates of zinc and copper, on the principle of the former metal being positive in its electrical relation to the latter. These plates are united, and then are placed in a mahogany case, and between each pair there is a cell or space; these cells are to be filled with a very dilute acid solution, usually composed of nitric and sulphuric, or muriatic acids, in a considerable proportion of water. The grand battery of tho Royal Institution consisted of 2000 double plates, constituting a total surface of 128,000 square inches; the cells were filled with a diluted acid, composed of water, in the proportion of 60 parts, to one part each, of sulphuric and nitric acid. The effects produced, and which are described in Sir Humphry Davy's Elements of Chemical Philotophy, may be conceived, when it is stated, that "When any substance was introduced into this arch," (i.e., the fire produced by the two opposite poles of the two wires,) "it became instantly ignited; platinum melted as readily in it as wax in the flame of a common candle; quartz, the sapphire, magnesia, lime, all entered into fusion; fragments of diamond, and points of charcoal and plumbago rapidly disappeared, and seemed to evaporate in it, even when the connexion was made in a receiver, exhausted by the air-pump: but there was no evidence of their having previously undergone fusion." An improvement in Voltaic troughs has been announced by Doctor Faraday, whereby increased action is made compatible with a great reduction in the dimensions of the instrument. See Experimental Researches on Electricity, 10th series, from the Philosophical Transactions, Part ii. for 1835.

But the most important discovery in electro-chemical science, appears to be that of the " Absolute quantity of electricity associated with the particles or atoms of matter" by Dr. Faraday: the experiments described in the sixth series of his Researches, appear to be conclusive. Paragraph 853 will convey some idea of tho stupendous volume of the ethereal fluid which enters into the composition of water; or is required to develop its gases. "Now it is wonderful to observe how small a quantity of a compound body is decomposed by a certain portion of electricity. Let us, for instance, consider this, and a few 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, Hz of an inch in thickness, red-hot, in the air, during the whole time; and if interrupted any where 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 illustrated in the beautiful experiments of Mr. Whoatstone, (Phil. Mag., ] 833, p. 204,) 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 quantity 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."

Again, in par. 854-5, we find that the relation between the conduction of electricity, and the decomposition of water is so close, that one cannot take place without the other: also, that for a given, definite quantity of electricity passed, an equally definite and constant quantity of water, or other matter is decomposed; and that the agent, which is electricity, is simply employed in overcoming electrical powers in the body subjected to its action; On these grounds, " it seems a probable, and almost a natural consequence that, the body which passes is the 'equivalent of, and therefore equal to, that of the particles separated; 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." New Researches, Sixth Series, pp. 116, 117.

This view of the subject gives an almost overwhelming idea of the extraordinary quantity 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.

I view the experiments of Dr. Faraday with astonishment, and hesitate to propose a doubt concerning his inference that the quantity of decomposing electricity which passes is the equivalent of that which retains the elements oxygen and hydrogen together, in the form of fluid water. But it occurs to me, that if water contains a definite volume of the ethereal fire, called electricity, in a state of neutrality and repose, this neutrality is disturbed by the voltaic current, and thus the two elements are separated in the state of gas. Now, is it not reasonable to infer, that the increased volume which the gases occupy, is produced by the vast quantity of electricity with which they combine, and by which they are retained in their aerial form. The electricity of the fluid water may pass ofi"; but that conducted from the two polar of the battery, appears to be associated with the elements, electrolyzing one with the electricity of hydrogen, and the other with the electricity of oxygen. Let us consider the instruments we find employed—a powerful current—two active poles{Electrodes) —a compound body, (water,) as the electrolyte, decomposable into two aerial gases, of very different specific gravities, capable of re-uniting with a loud explosion, and the extrication of a brilliant flash of light! Do we not perceive cause to admit the existence, and antagonist energy of two powers; and are we remote from the truth, when we hazard the conjecture that in Electricity and Magnetism, we discover these two powers?

96. Water may be produced synthetically—». e. by the union of the gases. 1st, By firing them with the electric spark in the detonating tube, (fig. 2,) placed securely in a mercurial p. 2 pneumatic trough, or in a basin containing mer- Fl, cury. Thus, A is a very strong glass tube, with c°4. lr°c two gold or platinum wires, cc, fitted into the two projections of the tube; the extremities of these wires within the tube, are about one-eighth of an inch apart, B is a basin containing the mercury m. The tube being first filled with mercury, to displace the air, is to be introduced into the basin, and then, a cubic inch of a mixture of the two gases, in the proportion of two parts of hydrogen to one part of oxygen, is to be passed into the tube; hold the tube firmly, and explode the gases by the electric spark: they will disappear, and by frequent repetitions of the process, a sensible portion of water will be obtained. The experiment may be varied, by filling the tube with pure water, the basin containing water also; then decompose the water by the voltaic electricity, and when the gases have been formed in sufficient quantity to displace all the water above the points of the wires, the first spark that passes through the gaseous volume will explode it, and the water will again rise and fill tho tube. Thus, the same experiment will exemplify the analysis, or decomposition of water, and the synthesis, or re-formation of the fluid, from its own gaseous products.

2nd. By combustion; for as water, or its elements, exist in all vegetable productions, the combustion of such substances, and of all other things with hydro-carbonous bases, (i. e., such as are composed of hydrogen and carbon,) always produces water, or watery vapours. Thus, the combustion of alcohol, (vinous spirit,) and of the gas called carburetted hydrogen, which is employed for lighting the streets, always yields a very large quantity of water, for their hydrogen unites to the oxygen of the atmosphere, and water is the product.

By pressure. In a memoir read to the National Institute of France, M. Biot announced the fact that a mixture of hydrogen and oxygen gases, may be made to explode by mechanical compression. This mixture was introduced into a strong metallic syringe, furnished with a glass bottom, and a sudden stroke was given to the piston. An extremely brilliant light appeared, accompanied with a loud detonation, and the glass bottom was forcibly driven out. This result affords proof presumptive, that the gaseous condition of the two elements is maintained by the volume of ethereal fire which is combined with, or interposed between their ultimate atomic particles!

97. They who are desirous to obtain farther information concerning the great variety of processes by which water may be produced, or decomposed, are referred to Lavoisier's Elements, Henry's Epitome, Parkes's Rudiments of Chemistry, and Faraday's New Researches. These works contain also, references to excellent plates, illustrative of the apparatus employed. Enough has been said here, to prove the accuracy of the generally received opinion concerning the compound and decomposable nature of water; and with one quotation from the sixth chapter of Dr. Henry's Epitome, I shall conclude the first part of this section. After stating that water is formed by the union of the two gases, he adds, " the water produced, is not, however, to be considered as a compound of the two gases, but only of their bases; for the light and caloric which constituted the gases,-escape, in considerable part, during the combustion*. Every gas, it must be remembered, has at least two ingredients; the one, gravitating matter, which, if separate, would probably exist in a solid or liquid form; the other, an extremely subtile fluid, termed caloric, (and perhaps, light,) is a common ingredient both of hydrogen and oxygen gases: but the two differ, in having different bases. The basis of the one is called hydrogen, and of the other, oxygen; and icater, may, therefore, be affirmed to be a compound of hydrogen and oxygen."

* The reader should, I conceive, endeavour to get rid of the erroneous impressions produced by the use of the term caloric. I therefore would urge him, wherever homay meet with it, to substitute that of electricity, or of elementary fire; the terms are synonym ous, expressive of a real active principle, which as far as it is capable of being understood, will account for all the phenomena of light and heat.

Part II.
INVESTIGATION OF THE CONSTITUENTS OF WATER.

98. Of the nature of hydrogen. The term hydrogen was given by Lavoisier, and other French chemists, to that base or radical, which, when in combination with oxygen, constitutes water. Lavoisier thus accounts for the origin of the term: water contains another element as its constituent base or radical; and for this proper principle or element we must find an appropriate term. None that we could think of seemed better adapted than the word hydrogen, which signifies the generative principle of water, from vScop, aqua, and yeivofiai, gignor. We call the combination of this element with caloric, hydrogen gas; and the term hydrogen expresses the base of that base, or the radical of water. "Hydrogen in the state of gas, dissolves carbon, sulphur, phosphorus, and several metals: we distinguish these combinations, by the terms, carbonated hydrogen gas, sulphurated hydrogen gas, and phosphorated hydrogen gas." The latter gas is remarkable for the property of taking fire spontaneously, upon getting into contact with atmospheric air, or what is better, with oxygen gas."Elem. edit. 1802. Vol. i., p. 141-165.

"Hydrogen," says Parkes, "is the base of the gas, which was formerly called inflammable air; and is, when in the aeriform state, the lightest of all ponderable things." "Hydrogen gas is only onefourteenth of the weight of atmospheric air, and occupies a space 1/500 times greater than it possessed in its aqueous combination. Hydrogen is continually emanating from vegetable and animal matters during their decay, and is a certain consequence of their putrefaction; it is also evolved from various mines, volcanoes, and other natural sources. The ignis-fatuus, or will-o'th,-icisp, originates from decayed vegetables, and the decomposition of pyritic coals*: it consists generally of hydrogen combined with carbon, and perhaps occasionally with phosphorus or sulphur."—(Rudiments, No. 115, 119, 220.)

Hydrogen gas can never be obtained pure, but by the decomposition of water; for experiments, it is usually procured by pouring sulphuric acid, formerly called oil of vitriol, diluted with 5 or 6 times

• Pyritic, that U an union of su/p/mr with a metal.

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