water, positive electricity will pass from the latter, through the galvanometer, to the former; because a concentrated solution is formed on the surface of the latter by evaporation of the water. With a spatula heate only to 60°, the direction of the current is the reverse of that just mentioned [possibly from thermo-electric action]. A current like the last is produced in solutions of Glauber's salt of all strengths, with a platinum spatula heated either to 60° or to redness. (Walcker.)

Salts and Metallic Chlorides with Salts and Metallic Chlorides. With aqueous solutions of the following substances (App. 2) positive electricity goes from the first-mentioned, through the galvanometer, to the last-mentioned: From chloride of potassium or chloride of mercury to ferrocyanide of potassium; from concentrated solution of sulphate of alumina to sulphate of potash; from chloride of zinc to common salt; from perchloride of iron to chloride of potassium; from nitrate of copper or nitrate of silver to nitrate of potash; from chloride of gold to chloride of potassium, sodium, or zinc, or perchloride of iron; and from chloride of platinum to chloride of ammonium, potassium, or sodium. (Walcker.)-From nitrate of copper, positive electricity goes in considerable quantity through the galvanometer to sulphate of zinc. (Berzelius.)-Chloride of lead, protochloride of mercury, or chloride of silver, fused in one arm of the U-tube (App. 5) sends a small quantity of positive electricity through the galvanometer to chloride of potassium fused in the other arm. (Dulk & Moser.)

Salifiable bases with Water. From hydrate of potash or soda, as also from aqueous solution of potash or soda, positive electricity goes through the galvanometer to water. (Becquerel, who formerly obtained the contrary result; Fechner.); also, from aqueous solution of potash to water, and from concentrated to dilute solutions of ammonia, potash, or soda. (Walcker.) [This seems more in accordance with the hypothesis.]

Salifiable bases with Salts. From solution of nitre, a small quantity of positive electricity goes through the galvanometer to solution of potash (H. Davy), and from solution of chloride of barium, through the galvanometer, to ammonia. (Walcker.)

Salifiable bases with salifiable Bases. Hydrate of alumina, oxide of zinc, or oxide of lead freshly precipitated by potash, held in the forceps (App. 1) and dipped into the liquid in the spoon, sends positive electricity through the galvanometer to solution of ammonia, potash, or soda, and thus acts the part of a dilute acid. (Becquerel.)-From fused oxide of antimony (not from oxide of bismuth), positive electricity goes through the galvanometer to fused oxide of lead. (App. 5; Dulk & Moser.)

Metals with Metals. On dipping zinc, tin, or lead into mercury, positive electricity goes from the mercury, through the galvanometer, to the other metal, in consequence of the combination of the metals. (Dulk & Moser, Pogg. 42, 91.)-On dipping the platinum ends of the galvanometer into the two arms of the U-tube filled with melted tin, allowing the tin to cool, and then heating only one arm, a thermo-electric current becomes manifest; but this current does not increase when the arm of the tube is heated to the temperature at which the platinum combines with the tin, producing a kind of combustion. (Faraday.)

Sir H. Davy lays down the following series of liquids, each of which sends positive electricity through the galvanometer to those which follow it: Nitric, hyponitric, sulphuric, and phosphoric acid, vegetable acids, hydrocyanic acid, hydrosulphuric acid, potash, soda, baryta, ammonia.

Experiments with three liquids. For these experiments, App. 2 is applicable, when the bundle of asbestus-threads contains a liquid different

from those in the two vessels; and App. 9, when the three vessels and the siphon or threads are filled with different liquids.

If a (App. 9) contains nitric acid, c soda, and b nitric acid, c being connected with b by a siphon filled with nitre, and a with b by a bundle of asbestus, positive electricity goes from a through the galvanometer to b, and is more than doubled in quantity when hydrate of soda is placed upon the asbestus. A similar result is obtained when hydrochloric or sulphuric acid is used instead of nitric acid, and common salt instead of nitre. (Becquerel.) [The current excited by the acid between a and c, the direction of which is from a to the galvanometer, is not completely neutralized by the two opposite currents produced by the action of the acid in c on the saline solution in i, and of the latter on the soda in c.]

If a (App. 2) contains nitric acid, b concentrated solution of potash, and the cotton-wick, h, solution of Glauber's salt, about twice as much positive electricity goes from the acid through the galvanometer to the potash, as would be set in motion, if a contained nitric acid, and b and h Glauber's salt,- or a and h Glauber's salt, and b potash. [In the first case, the two currents produced by the acid acting on the Glauber's salt, and this on the alkali, assist each other; in the other two, one only of these currents is produced.] If the first experiment lasts some time, and the threads h are not above three inches long, the deflection of the needle increases suddenly from 5° to 20°, when the acid comes into immediate contact with the potash. The acid and alkali come most quickly into contact in the wick when the latter contains the salt which is produced by the combination of the two, e. g., nitre in the case of nitric acid and potash, and Glauber's salt in that of sulphuric acid and soda; if, on the other hand, the wick contains pure water, the infiltration takes place very slowly: no deflection is produced at first, but after about twelve minutes, a strong deflection of 20°. When the wick is six inches long, no increase of the current takes place, even if it contains a saline solution; on the contrary, the current becomes gradually weaker; because, after a time, no more chemical combination takes place in the wick. The deflections of the needle produced at the commencement of the action are as follows,-it being observed that the first-named substance is placed in the vessel a, the second in the wick h, and the last in the vessel b,-and that in each case, the positive electricity goes from the first substance, through the galvanometer, to the last-named:-With nitric acid, Glauber's salt and potash, 5°;-nitric acid, Glauber's salt, Glauber's salt, 3°;-Glauber's salt, Glauber's salt, potash, 3;-nitric acid, nitre, potash, 4°;-nitric acid, nitre, nitre, 2°;-nitre, nitre, potash, 2°; a mixture of 2 measures of oil of vitriol with 1 measure of water, Glauber's salt, soda, 5°;-the same mixture, Glauber's salt, Glauber's salt, 3;-Glauber's salt, Glauber's salt, soda, 2°;-mixture of 2 measures of oil of vitriol and 1 water, nitre, soda, 12°;-the same mixture, nitre, nitre, 5;-nitre, nitre, soda 3°;-the same mixture of oil of vitriol and water, sal-ammoniac, soda, 16°;-the same mixture, sal-ammoniac, sal-ammoniac, 6°;--sal-ammoniac, sal-ammoniac, soda, 6°. (De la Rive.)

If the vessels a, b, (App. 9) are filled with solution of nitre, and the wicks g, i, saturated with it-the vessel c containing nitric acid, and a piece of hydrate of potash being placed upon the wick i at x, where it dips into the nitric acid-a current is set up from the nitric acid through the galvanometer to the hydrate of potash, much stronger than that which is produced by the use of aqueous solution of potash,-because the former becomes more heated by combining with the nitric acid;-and, generally

speaking, the current goes constantly from the colder body to that which is most heated during the combination: moreover, the phenomenon is thermo-electric [?]. (Nobili.)

Fechner, proceeding upon the contact-theory-according to which, metals excite an electric current, even in liquids which do not act chemically upon them-endeavoured to get rid of the effect which, according to this view, might be expected to arise from dipping the platinum te minations of the galvanometer into two different liquids, by immers these platinum terminations in two cups, a, b, (App. 10) containing the same liquid-placing the two liquids whose mutual action was to be investigated, in two other cups, a, B, and connecting the four cups by three siphon-tubes. The siphons g, i, contained the same liquid as the cups a, b; the siphon h either the liquid in a or that in ß. [By this arrangement, a complicated action is always obtained: not only is a current produced by the mutual action of the liquids in a and B, but likewise by that of the liquid in a upon that in a, and of the liquid in 6 on that in ß; and the direction and strength of the current is the resultant of the sum or difference of these three actions.] The following are some of the numerous results obtained in this manner:-the liquid in the cup a is always that from which positive electricity passes through the galvanometer to the cup B.

Glauber's salt in a, b, sulphuric acid in a, potash in B.-Common salt in a, b, potash in a, hydrochloric acid in B.-Spring water or nitric acid in a, b, nitric acid in a, potash in B.-Nitre in a, b, potash in a, sulphuric acid in 8;-Nitre in a, b, sulphuric acid in a, nitric acid in B.

In the following experiments of Fechner, the three liquids,-solution of potash, nitric acid, and solution of nitre, were distributed in various ways among the 4 cups, and the following deflections were obtained.

1. Nitre in a, b, nitric acid in a, potash in 8; positive electricity goes from a through the galvanometer to b, deflecting the needle 40°. [The principal current is excited by the action of the nitric acid on the potash; but the two more feeble currents produced by the action of nitric acid on nitre and potash on nitre, take the direction opposite to that of the first and weaken it.]

2. Potash in a, b, nitric acid in a, nitre in ; positive electricity goes from 6 through the galvanometer to a; deflection 33°. [In this case also the principal current produced by nitric acid and potash between a anda, which, according to the arrangement, must take the opposite direction to that in 1, is weakened by the two currents produced by nitric acid and nitre, and by potash and nitre, in the same degree as in 1; hence the deflection is nearly the same.]

3. Nitric acid in a, b, potash in a, nitre in B; positive electricity goes from a through the galvanometer to b: deflection 48°. [Here again the two feebler currents weaken the principal current; hence the deflection is about the same.]

4. Nitric acid in a, potash in b, nitre in a and B; positive electricity goes from a through the galvanometer to b, producing a deflection of 140°, which lasts much longer than in the former cases. [In this case, positive electricity goes from the nitric acid through the galvanometer to the nitre, and likewise from the nitre through the galvanometer to the potash; the united action of these two feebler currents produces a deviation greater than that which results from the action of a principal current weakened by two feebler currents.]

5. Nitric acid in a, nitre in b, potash in a and 8; positive electricity

om a through the galvanometer to b; deviation 164°. [The princurrent produced by the action of the acid on the potash is opposed by the feebler current resulting from the mutual action of potash nitre.]

6. Potash in a, nitre in b, nitric acid in a and ẞ; positive electricity es from 6 through the galvanometer to the potash, producing a deviation 168. Here again the principal current produced by the action of otash and nitric acid is counteracted only by the feebler current realting from nitric acid and nitre.]

Becquerel's Oxygen-circuit. A glass tube (App. 11) is closed at its ower extremity with clay moistened with a concentrated solution of otash; the tube is then filled with strong potash-solution and its lower part dipped into a vessel filled with strong nitric acid. If now the platinum ends of the galvanometer be immersed in the two liquids, a large quantity of oxygen gas will be developed on the surface of the platinum in the potash (it may be most conveniently collected by having the platinum wire which dips into the potash cemented into a glass tube open at the bottom, this tube being afterwards filled with potash and inverted), and nitrous acid will accumulate in the nitric acid, colouring it first green and then blue: at the same time, positive electricity will pass from the acid through the galvanometer to the potash. The action continues for several days. But the electric current is very feeble in comparison with the copious evolution of gas; it is sufficient indeed to separate copper, when passed through a solution of blue vitriol, but not to heat fine platinum wire. (Becquerel.) Jacobi likewise obtained a large quantity of oxygen gas, and at the same time an electric current which decomposed iodide of potassium, but not sulphate of copper.-Moser & Dulk (Pogg. 42, 91) who obtained a remarkably large quantity of oxygen gas, found, contrary to Becquerel's statement, that the electric current thus excited produced cold as well as heat in Peltier's apparatus.-Mohr obtained no oxygen gas with this apparatus, and Pfaff only a few bubbles in several hours. These negative results, possibly arising from differences of manipulation or in the materials employed, cannot be considered of equal weight with the often verified statement of Becquerel, however enigmatical it may appear that a chemical action accompanied by so copious an evolution of oxygen gas, should produce a current so feeble in comparison. It may perhaps be suspected that if the clay be moistened with a solution of common salt or of potash containing chloride of potassium, nitrous acid and chlorine, together with a salt of nitric acid, may be produced by the action of the nitric acid on the chloride of sodium or potassium, the nitrous acid going over to the nitric acid, while the chlorine, taking the opposite direction, converts the potash into chloride of potassium and oxygen gas. I have however satisfied myself that, even when the nitric acid and potash are perfectly free from chlorine, oxygen gas (capable of igniting a glowing slip of wood and condensing with nitric oxide gas) is abundantly developed.

If the nitric acid in Becquerel's apparatus be replaced by a mixture of 2 parts oil of vitriol and 1 part water, only a small quantity of oxygen gas is evolved on the platinum immersed in the potash, and a little hydrogen on the platinum in the acid, an electrical current being also produced in the same direction, capable of decomposing, not only iodide of potassium, but also sulphate of copper. (Becquerel.) Mohr obtained with the same arrangement neither gas nor electric current. I have also tried the experiment with the same clay and potash that were used

in the successful experiment with nitric acid, sometimes using concen trated sulphuric acid alone, sometimes diluted with one-half water,-but never obtained a trace of gas. Did Becquerel's oil of vitriol contain nitric acid?

The existence of electric currents in the animal body appears to connected with the development of electricity in the combination of aci and alkalis. The external skin is acid, the mucous membrane of alimentary canal (with the exception of the stomach) alkaline, the ston is strongly acid, the liver alkaline. On placing one platinum termin tion of the galvanometer on the skin, and the other in the mouth, positiv electricity goes from the skin through the galvanometer into the mout If one end of the galvanometer touches the mucous membrane of e stomach of an animal, the other the gall-bladder or the inside of thaiver, a deflection of the needle is produced, twice as great as in the preceding experiment, continuing after the death of the animal, and only diminishing a little because the fluids are no longer renewed. Even when the stomach and liver are taken out of the animal, the same action is produced. Similar currents are also excited between stomach and spleen or urinary bladder, and between bladder and intestines; on the contrary, no currents are produced between the two kidneys, between two pieces of the small intestines, or between the liver on the one side, and the pancreas, spleen, or intestines on the other. (Donné, Ann. Chim. Phys. 57, 405.)

Similar currents are also excited in plants. If one extremity of the galvanometer be inserted into the stalk of an apple or pear, the other into the opposite end of the axis, positive electricity passes from the latter through the galvanometer to the stalk. In peaches and apricots, the electric current takes the contrary direction: but no current is excited when the ends of the galvanometer are inserted into the fruit at right angles to its axis. If a fruit be cut into two parts perpendicularly to its axis, the juice pressed out of each of them, and placed in two cups connected by a wet strip of paper (App. 2), an electric current will be developed in the same direction; but if the fruit be split in the direction of its axis, the liquids expressed from the two halves produce no current. The current is therefore due to the difference of chemical composition between the juice in the neighbourhood of the stalk, and that at the other end of the fruit, although both are acid.

b. By Decompositions, effected by the agency of Heat or Light. Bodies, at the moment of separation from one another, take up the kind of electricity opposite to that which they exhibited during combination. [According to what has already been said (pp. 328... 330), it must be supposed that when water combines with acids, negative electricity from the water and positive electricity from the acid combine to form heat; and when the water is separated from the acid by evaporation, it must again take up the negative electricity which it has lost, while the acid must recover its positive electricity. This is effected by the decomposition of part of the heat present, the elements of which are divided between the water and the acid. It appears, however, that very small quantities of water and acid get separated from one another without having time to recover their lost electricity. These small quantities of separated aqueous vapour and acid then decompose other portions of heat to make up the deficiency. Thus, the water takes negative electricity, and sets positive electricity free, while the acid takes up positive electricity; so that free negative electricity may be detected in the vessel.