c. There was every reason to suppose, that the slight dimunition produced by the mixture of the hydrogen with nitrous gas in the last experiment, as well as the residual gas of the oxygen, were owing to common air held in solution by the distilled water, and given out from it during the process. To ascertain if the gases could be obtained perfectly pure, when water deprived of its loosely combined air by boiling was employed, the two tubes were filled with water that had been boiled for more than eight hours, and that was yet so hot as to be painful to the fingers; the glasses were filled with water of the same kind, and the process conducted as before; the tubes being suffered to cool before the communication was made, gas was given out very rapidly from the water connected with the silver; but very slowly from that connected with the zinc. During the whole of the process, no globules of air formed on the sides of the tubes, as in the last experiment. In five hours the tube connected with the silver contained fifty-six grain measures of gas. That connected with the zinc contained only fourteen measures. The fifty-six measures gave no diminution with nitrous gas, and appeared by the test of detonation, to be pure hydrogen. The fourteen measures tried by the tests mentioned in the last experiment, appeared to be oxygen, mingled with no perceptible quantity of other gas. In this experiment, as in the last, the gold wires were not apparently acted upon, nor was their colour in the slightest degree altered; the deficient proportion of oxygen, there was every reason to believe, was owing to the absorption of that gas in the nascent state, by the boiled water. Boiled water was now exposed to, and agitated in oxogen over mercury, till it was judged to be saturated with that gas. The tube connected with the zinc was filled with this water; the other tube was filled with common boiled water. The galvanic process was continued seven hours. In this time the water connected with the zinc had given out twenty-seven grain measures of oxygen, apparently pure; from the water connected with the silver, fifty-seven measures of hydrogen had been extricated.

d. Having thus ascertained that oxygen and hydrogen, nearly in the proportions required to form water, could be separately produced from quantities of water, having no communication with each other, except by means of the dry metallic conductors and muscular fibre. I next endeavoured to ascertain, if the contact of the metallic wires, with the metallic plates of the apparatus, were essential to the effect. The conducting ends, i. e., the silver and zinc, were made to communicate with two glasses of water, by means of two unconnected pieces of muscular fibre. A piece of silver wire was made the medium of connexion between the glasses. Immediately after the connection, I was surprised by seeing that end of the wire in the water communicating with the silver calcining; whilst gas was given out from that part of it in the vessel communicating with the zinc; as was the case in the broken circuit described by Mr. Nicholson. When the tubes with gold wires, con

nected by silver wires, were employed, oxygen was given out in the water connected with the silver, and hydrogen in that communicating with the zinc. In none of these experiments could any production of gas from the muscular fibre be perceived; but the parts exposed to the water became whiter than before.

When (the glasses being connected with the apparatus by muscular fibre) the communication between them was made through my body by means of the gold wires in the tubes; one being in contact externally with my right hand, the other with my left, oxygen was produced as before in the glass connected with the silver, and hydrogen in that connected with the zinc. When I made the communication, holding a silver wire partly plunged into the water connected with the silver, in my right hand, the fingers of my left hand being in the other glass, the silver wire became slowly oxydated, and no gas was perceptibly given out in either of the glasses. When on the contrary, I introduced my hand into the silver glass, and the wire into the zinc glass, gas was given out round the wire, no oxydation took place, and no gas was extricated in the silver glass.

When the glasses were made to communicate both with the machine, and with each other, by means of muscular or vegetable fibre; and metallic wires introduced into either or both of the glasses, and wholly or partially covered with water, no gas was given out from them, and no apparent chemical change took place.

Reasoning on this separate production of oxygen and hydrogen, from different quantities of water, and on the experiments of Mr. Henry, jun. on the action of galvanic electricity on different compound bodies,* I was led to suppose, that the constituent parts of such bodies (supposing them immediately decomposable by the galvanic influence) might be separately extricated from the wires, and in consequence obtained distinct from each other.

a. I filled two of the small tubes mentioned in b 1. with strong solution of caustic potash, and inverted each of them in a glass filled with the same substance; the glasses were made to communicate with each other by means of muscular fibre, and the gold wires in the tubes connected with the ends of the pile. Gas was produced much more rapidly in this process from both wires, than in the experiment with simple water. In three hours no deposition had taken place in either of the glasses, nor were the gold wires sensibly acted upon. The gas given out in the tube connected with the zinc, measured exactly 37 grain measures, and proved to be oxygen absolutely pure, for with 80 measures of nitrous gas, containing about nitrogen, it diminished to less than 3 measures. The gas given out in the tube connected with the silver, was equal to rather more than 72 grain measures. It gave no diminution with nitrous gas, and two 20 grain measures of it, fired with rather more than one 20 grain measure of oxygen, containing about 106 nitrogen, left a globule of air hardly perceptible.

♦ Phil. Journ. Vol. iv. p. 224.

Surprised at these results, which proved that no decomposition of patash had taken place, and that that substance in this mode of operating, only enabled the galvanic influence to extricate oxygen and hydrogen more rapidly from water, I was induced to operate upon this substance in the way of direct communication. Two gold wires were passed through holes in the side of a small glass tube closed at one end, and cemented so as to be distant about the eighth of an inch. This tube was filled with solution of potash, and inverted in glass filled with the same substance; the gold wires were made to communicate with the ends of the pile. Gas was produced rapidly from both wires, but most from the silver wire; the gold was not acted upon, and no deposition took place. When near a quarter of a cubic inch of gas had been collected, it was transferred to a detonating tube, and fired by the electric shock over mercury, it gave a vivid inflammation, and left a globule of air not equal to of the whole quantity.

b. Solutions of caustic ammoniac were exposed to the galvanic influence in the two tubes with gold wire, and connected by mus. cular fibre. Gas was given out very slowly in the tube connected with the zinc, and the gold wire was evidently acted upon, being in some parts corroded, and in other parts covered by a yellow deposit. In the tube connected with the silver, gas was given out more rapidly and the gold was not altered in appearance. In five hours the gas in the zinc tube was equal to 5 measures, and proved to be a mixture of nearly 3 oxygen, and 2 of nitrogen. The gas in the silver tube measured 31 grains, and appeared to be hydrogen, mingled with a minute quantity of nitrogen. I repeated this experiment several times, to ascertain if after the solution of ammonia had been long galvanized, the proportion between the gases would be different. The gas given out in the zinc tube was always to that in the silver tube nearly as 1 to 6, but the quantity of oxygen appeared to increase towards the end of the process. A quantity of solution of ammoniac, the same as that used in the experiment exposed to heat in a mode described in Research. Chem. and Phil. page 241, readily produced of its bulk of unabsorbable gas, which gave no diminution with nitrous gas, and appeared to be nitrogen. In every experiment yellow deposit was formed upon the gold in the zinc tube; muriatic acid poured upon some of this yellow deposit slowly dissolved it, a little nitrogen being given out during the solution.

When a solution of caustic ammoniac was exposed in the silver tube, and water in the zinc tube, the gold wires were not perceptibly altered, and oxygen was given out in the zinc tube, and hydrogen in the silver tube, nearly in the proportions required to produce water. When on the contrary water was connected with the silver, and solution of ammoniac with the zinc, hydrogen was produced from the water; the zinc gold wire was corroded, and the mixture of oxygen and nitrogen to the hydrogen, as six to one, (one to six?) was produced as before.

c. Concentrated sulphuric acid was galvanised in the double tubes

connected by muscular fibre. The gold wire in the zinc tube was not dissolved or corroded, and in a great length of time 41 measures of gas, which proved to be pure oxygen, were given out from it. But little gas was given out in the silver tube, the acid in it was clouded with a white substance, which was evidently sulphur; it was perpetually produced round the point of the wire. 15 measures of gas were evolved, which gave rather greater diminution, fired with oxygen, than pure hydrogen; hence they might possibly have been partially sulphurated hydrogen.

When solution of caustic potash was put into the silver tube, and sulphuric acid into the zinc tube, pure hydrogen was disingaged in the silver tube, and pure oxygen in the zinc tube; the same phenomena took place when water was employed instead of solution of potash.

When water was connected with the zinc, and sulphuric acid with the silver, the products were the same as when pure sulphuric acid was used in both tubes. When very diluted sulphuric acid was employed in both tubes, oxygen and hydrogen, nearly in the proportions required to form water, were separately evolved.

d. The tubes were filled with pure solution of muriatic acid, and the communication made as before. No gas was given out in the zinc tube, and the gold in it was very much corroded; 30 measures of pure hydrogen were collected in the silver tube, the gold in which was not perceptibly acted upon. When water was made to communicate with the zinc, and muriatic acid with the silver, neither of the gold wires were acted upon, and 22 measures of oxygen were collected from the water, and 41 of hydrogen from the muriatic acid. When water was connected with the silver, and muriatic acid with the zinc, the same phenomena took place, as when pure muriatic acid was used in both tubes.

e. Concentrated solutions of nitric acid were galvanised in the tubes, 19 measures of pure oxygen were produced in the zinc tube. A globule of gas, only, not equal to half a measure was produced in the silver tube, and the acid became green on the top. The globule of gas did not diminish with oxygen, it was too small to be tried by other tests. The gold wires were not acted upon.

When nitric acid was connected with the zinc, and water with the silver, oxygen and hydrogen were separately produced. When water was connected with the zinc, and nitric acid with the silver, oxygen was given out from the water; no gas was given out from the acid, and it became green.

In the experiments on the sulphuric and nitric acids, it is most probable, that the acids were decomposed by the nascent hydrogen in the silver tube. In the experiments on the muriatic acid and ammoniac, the deficiency of the oxygen in the gold tube most probably, partly arose from the oxydation of the gold, in consequence of what may be called predisposing affinity. In these processes none of the compound bodies appear to have been immediately decomposed by the galvanic influence.

The difference between my results and those of Mr. Henry, may be accounted for from the difference between our modes of operating; I suspect, however, that on repeating his experiment on the solution of potash under new circumstances, that ingenious chemist will find reasons for altering his conclusions with regard to the decomposition of the alkali.

Judging from the rapidity with which the gases were extricated, solution of potash would seem to be a better conductor than water, water a better conductor than solution of ammoniac, and solution of ammoniac, better than either of the three mineral acids. Possibly phosphoric acid, and other acids, may be decomposed when exposed to nascent hydrogen, produced under the galvanic influence. If the ratio between the quantities of the oxygen and hydrogen produced from the different wires, be always the same, whatever substance, are held in solution by the water connected with them, this nascent hydrogen will become a powerful and accurate instrument of analysis.

Additional Experiments on Galvanic Electricy. By MR. DAVY, Superintendent of the Pneumatic Institution.

SIR, THE earlier experimenters on animal electricity noticed the power of well-burned charcoal to conduct the common galvanic influence. I have found that this substance possesses the same properties as metallic bodies in producing the shock and spark+ when made a medium of communication between the ends of the galvanic pile of Signor Volta.

I have likewise found that perfectly well-made charcoal, when connected with water or aqueous solutions in the galvanic circuit, effects changes in them analogous to those produced by metals; but connected with peculiar appearances.

1. Two long and thin slips of dry charcoal were connected with silver wires attached to the ends of a galvanic pile of 60 pieces. The points of the charcoal slips were immersed in a glass of water, at the distance of half au inch from each other; and the globules of air adhering to them being carefully removed, the communication made sure.

In about a minute, particles of gas began to form and evolve themselves round the point of the charcoal connected with the silver side of the apparatus. Near a quarter of an hour elapsed, before any gas was produced from the zinc side; the gas that was produced adhered to the charcoal in large globules, and did not pass through the water. As long as the communication was kept up, the silver charcoal gave out gas very rapidly.

The inventor of the galvanic pile discovered the conducting power of charcoal. His experiments were confirmed by Creve and Schmuck. See Pfaff on Animal electricity, page 48.

The spark is most vivid when the charcoal is hot.