minal of the galvanometer; a powerful deflection of the needle indicates the presence of an electric current and shows its direction to be from the alkali to the acid, the platinum serving merely as a conductor. It occurred to me, when performing this experiment, that an electro-motive combination might just as well be made of two vegetable substances, with platinum for conductor, provided only they were of a nature to act chemically upon one another, - an alkaloid and an organic acid, for instance. It also seemed to me not unlikely that, wherever two flavors are habitually conjoined in our cookery and eating, the reason why they mutually improve each other is because a certain amount of electric action is set up between the substances employed to produce them. The rationale of the right blending of flavors might be found partly, no doubt, in chemistry, but partly, also, in galvanism.

"Pursuing this idea, I tried pairs of eatables which generally go together, such as pepper and salt, coffee and sugar, almonds and raisins, and the like, and found that a voltaic current more or less strong was excited in every instance which I tested. Bitters and sweets, pungents and salts, or bitters and acids, generally appear to furnish true voltaic couples, doubtless in consequence of the mutual action of some alkaloid salt and an acid or its equivalent. As others may like to repeat or extend the experiments, I will describe shortly my mode of procedure: Cut two pieces of platinum foil about five inches by two and a half inches, and a number of pieces of filter-paper a trifle larger. Wellwashed linen is sometimes more convenient than filter-paper. Have a small wooden board near the mercury-cups of the galvanometer, and let a short copper or platinum wire, dipping into one of the cups, rest on the board. The substances to be tried must be brought to a state of solution, the stronger the better, by infusion, decoction, or otherwise. Suppose coffee and sugar are to be operated upon; solutions of both having been prepared, dip into each a slip of filter-paper; place one slip on one of the pieces of platinum foil, and the other on the second piece. Next lay the first slip and its foil on the board, with the metal touching the copper wire before mentioned. Lay the second slip with its platinum upwards, so that the coffee and sugar come into even contact with slight pressure, and immediately connect this upper slip, through a bit of copper wire, insulated from the touch, with the other terminal of the galvanometer. Deflection occurs instantaneously, and may be increased to a considerable vibration by breaking and making circuit at the right swing of the needle. After a few distinct vibrations, it is well to turn over the whole pile of slips just as they are, and connect opposite ends with the galvanometer, so as to reverse the current. This is desirable for the sake of confirming your previous observation, and of correcting any slight disturbing cause arising from the wire and mercury connectors, temperature of the hand, etc. It will be found that coffee and sugar have the same electrical relation to each other as zinc and platinum. Coffee, in fact, is the positive, sugar

the negative. I subjoin a table of the results of numerous experiments, conducted in the manner above described:

ELECTRO-POSITIVE.

:

ELECTRO-NEGATIVE.

Sugar (loaf).

Almonds,

Rhubarb (tincture),

Starch,

Starch caramel,

Gum caramel,

Cane sugar caramel,

Tea (black),

Tobacco,

Quinine (Howard's),

Horehound,

Lavender water,

Quassia,.

"It is somewhat difficult to eliminate from these experiments all error arising from difference of temperature, if the galvanometer is tolerably sensitive. Care must be taken to bring the pair of solutions operated upon to the same temperature before testing them; otherwise a thermo-electric current from the hotter to the

colder liquid may affect the needle, and mask the true electrical relation between the two, so far as it depends upon their chemical nature.

FRIGORIFIC MIXTURES.

The degree to which the temperature can be reduced by dissolving a salt in water, will, in general, be the greater in the proportion to the dissolved quantity of the salt. Since this quantity depends upon a certain temperature, it will be necessary, in order to obtain the greatest effect, to bring the salt and menstruum together precisely in the proportion in which they yield a saturated solution at the desired low temperature. Any excess of water beyond that needs also to be cooled down, and therefore consumes part of the effect. The fact that this point has generally been left out of view is the cause that the data as to frigorific effect and lowest temperature vary considerably with different observers. The best and safest way is to bring together the ingredients in such conditions that an instantaneous solution must immediately take place, that is, the salt in as fine a state of division as possible, and very slightly in excess of the calculated proportion, after both salt and water have remained for 12 to 18 hours in thin glasses in the same room together, to allow them to equalize their temperature with that of the room. In the following comparative table of averages the results were obtained by adding the water to the salt and stirring with the thermometer. The maximum lowering is attained within a minute at most.

FREEZING MIXTURE.

When citric acid and crystallized carbonate of soda in powder are stirred together, the mass gets into a pasty state, and in a short time becomes quite liquid. If equivalent proportions of the substances are used, the temperature falls from 60° F. to 80° F. The mixture, for a time, is full of air-bubbles, but soon becomes quite a clear, dense, syrupy liquid. The fluid obtained by mixing the powders becomes solid in a day or two, standing in a corked jar. The solid mass has the appearance of set plaster of Paris. The addition of a very little water appears to prevent this settling into a solid mass; but the chalky-looking citrate lies a long time in cold water without being dissolved.

NEW METHOD OF MAKING ICE.

A few days ago a number of gentlemen, by special invitation, witnessed the operations of a new invention which bids fair to be one of great practical value. It is a process of making ice and refrigerating by machinery, in a short space of time, at a comparatively small cost, and to an almost unlimited extent. The working of this machinery was exhibited on board the steamship "William Tabor," lying in the East River, at the foot of Nineteenth Street, and its utility satisfactorily shown to the spectators. This novel invention does two things: it makes ice with the thermometer at 90 degrees in the shade, and preserves meats and fruits for transportation. It accomplishes its purpose upon the chemical principle that if all the heat is extracted out of any object, it becomes intensely cold. The ice is made in this way: A small steam engine, by means of two pumps, subjects carbonicacid gas to a pressure sufficient to liquidize it. In a liquid state this gas has lost its heat, but recovers it again when converted into gas. Accordingly, a simple apparatus is contrived, by which the acid in a liquid state is made to surround small tubes filled with water. The acid then returns to its gaseous condition, and in doing so takes with it all the caloric out of the water leaving it solid ice. There is no limit to the number of these tubes or apartments of water, and a large quantity of ice can be formed at a time. Yesterday about 20 tubes were filled and frozen to an arctic rigidity.

Upon the same principle air can be rendered cold and dry by being passed through these tubes while carbonic acid is regaining its heat, and then can be pumped into an air-tight chamber. In this chamber, thus filled with dry, frozen air, any meat, fruit, or perishable article can be placed and preserved.

THE BATHOMETER.

This instrument admits of a combination in one sounding of three or more distinct methods of ascertaining and measuring these

depths. The discovery of the Messrs. Morse was that of the means of making a buoy which will retain its buoyancy under the enormous pressure of the deep sea. They took a hollow glass sphere between 3 and 4 inches in diameter, the glass only a tenth of an inch thick, and the sphere so light that it floated in water with half its bulk above the surface, and subjecting this fragile body in the cistern of an hydraulic press to a pressure of 7 tons on the square inch, which is the pressure at the depth of about 30,000 feet in the ocean, they found that the sphere was neither crushed nor permeated by the liquid. A tin or wooden tube, 4 inches or more in diameter, and of any required length, is filled with these glass spheres, and ballasted so that it will float upright in the water. An elongated sinker, also, of any required length and weight, is then suspended from the bottom of the tube, and so attached there that it becomes detached when the weight touches, or, if desired, when it is 100 feet, or any required distance, from the bottom, leaving the tube with its spheres to ascend to the surface. As this instrument moves with uniform velocity both in its descent and ascent, the time of its disappearence from the surface indicates the depth to which it has descended. But the inventors do not confine themselves to this mode of determining the depth. They enclose in their tube, and send down and bring back with it their proper bathometer, which is simply a bottle of water with a bag of mercury and water suspended from its neck, the water in the bottle being connected with the mercury in the bag by a glass tube, of very fine bore, passing from the bottom of the bag through an India-rubber stopper in the neck of the bottle into its interior. When this bottle and bag are placed at the bottom of the sea, the pressure of the external water, communicated through the bag and through the mercury in the bag and glass tube to the water in the bottle, compresses that water, and mercury is forced from the bag into the bottle, to supply the void caused by the compression. The amount of the mercury forced into the bottle is the measure of the compression of the water, and the compression of the water is the measure of the height of the compressing column, that is, of the depth of the sea. To facilitate the measuring of the mercury, there is inserted in the bottle, opposite the neck, a graduated tube of even bore, closed at its outer end, so that on inverting the bottle the mercury falls into this metre-tube, and the height of the mercury indicates the depth to which the bottle has descended.

All attempts to measure the deep sea with a line and sinker attached, as in ordinary soundings, have proved failures, and scientific men of the highest reputation, who have devoted much time to the investigation of the problem, have pronounced it impossible ever to send and recover a line with a sinker from the greatest depths of the ocean. Even in moderate depths the measurement by a line is very uncertain and unreliable, in consequence of the effect of currents, and of the drifting of the boat from which the soundings are made. The bathometer of the Messrs. Morse, it is asserted, will descend to, and return from,