the tube is covered with a slight coating of charcoal. This decomposition is similar to that which sulphureted hydrogen undergoes; for Cluzel has shown that this last is partly converted into hydrogen and sulphur by heat.

It will be recollected that iron at a red heat decomposes hydrocyanic acid. The elastic fluid collected is a mixture of equal volumes of azote and hydrogen. The greatest part of the carbon is deposited round the iron, and a small part combines with it. Copper and arsenic have no action on hydro-cyanic acid. Platinum appears to decompose it at a high temperature, but the result is the same as is produced by heat alone.

The oxides produce on hydro-cyanic acid a variable action depending on their affinity for oxygen.

Having placed barytes, recently prepared from its nitrate, in a glass tube heated to an obscure red, and made hydro-cyanic vapour pass over its surface, the barytes became slightly incandescent. It became soft, and then dried. No water was disengaged, but only pure hydrogen gas.*

This experiment shows that barytes decomposes hydro-cyanic vapour in a manner analogous to that in which it decomposes muriatic acid gas. But we obtain hydrogen in the first case, and water in the second, in consequence of the difference in the affinities of barium for cyanogen and chlorine.

Since hydro-cyanic acid in combining with barytes loses its hydrogen, the compound is a true cyanuret of barytes; when placed in contact with water, it ought to produce compounds analogous to the chlorates, iodates, or sulphites; that is to say, containing an acid composed of oxygen and cyanogen, which would be cyanic acid, strictly so called. But there is here a peculiar circumstance, which modifies a great deal the results; namely, cyanogen is a compound, and its elementary affinities appear more energetic than its resulting affinities. It is certain, at least, that by dissolving a cyanuret in water, we do not form a combination of oxygen and cyanogen. I shall soon examine this subject more particularly.

Instead of barytes, potash prepared by means of alcohol may be employed. The experiment may be made in a small curved glass tube, and it is more easy than the preceding one. Cyanuret of potash is obtained, and hydrogen is disengaged; but its quantity is greater than the hydro-cyanic acid could furnish, because the water which the potash contains contributes to the decomposition of a part of the cyanogen.

I likewise formed cyanuret of soda by passing hydro-cyanic vapour over dry carbonate of soda in a glass tube heated obscurely red-hot. The acid of the carbonate is disengaged, and an inflammable gas obtained, which is not pure hydrogen, because both this gas and

is

This experiment may be conveniently made with hydro-cyanic vapour mixed with azote or hydrogen in a small bent tube, heated by a spirit of wine lamp; but the incandescence will not be seen, as the absorption will be less rapid. While cold, barytes exercises no sensible action on hydro-cyanic vapour.

hydro-cyanie vapour are capable of acting upon carbonic acid at a high temperature, and of partly decomposing it.

I have already shown that the oxide of copper decomposes hydrocyanic acid completely at a red heat, and that water is obtained, and a mixture of one volume carbonic acid and half a volume of azote. But I wished to ascertain if the action of these two bodies would not be different at the common temperature. I accordingly introduced peroxide of copper into a tube with hydro-cyanic vapour mixed with hydrogen. The absorption took place by degrees; but was not so great as it would have been if all the vapour had been destroyed. Having turned up the tube to ascertain by the smell if any hydrocyanic acid remained, I observed with surprise that cyanogen had been formed, easily recognizable by the strong and penetrating odour which characterizes it. On exposing the oxide to a gentle heat, a good deal of water separated from it; so that it appears that hydro-cyanic acid is acted upon in the same manner by peroxide of copper as muriatic acid by peroxide of manganese. On putting oxide of copper into the liquid acid, diluted with water, the smell of cyanogen became very sensible in a few days, and the oxide became white on the surface. The peroxide of manganese absorbs completely hydro-cyanic vapour in a few hours. Water is formed; but cyanogen does not become sensible. I shall examine more particularly hereafter what takes place on this occasion.

The red oxide of mercury, when assisted by heat, acts so powerfully on hydro-cyanic vapour, that the compound which ought to be formed is destroyed by the heat disengaged. The same thing happens when a little of the concentrated acid is poured upon the oxide. A great elevation of temperature takes place, which would occasion a dangerous explosion if the experiment were made upon considerable quantities. When the acid is diluted, the oxide dissolves rapidly, with a considerable heat, and without the disengagement of any gas. Nothing is obtained but the substance formerly called prussiate of mercury.

When the oxide is placed in contact with the vapour of hydrocyanic acid, mixed with hydrogen, without applying heat, the vapour is absorbed in a few minutes. On emptying the tube of the hydrogen in order to fill it with a new mixture, that the result might be the more sensible, the absorption of the vapour was as complete as the first time, and the hydrogen remained with the volume which it ought to have had, which shows that it had no part in the phenomenon. After some similar operations, the oxide adhered to the sides of the tube. Having collected it at the bottom of the tube, and applied a gentle heat, a good deal of water was evaporated.

Hence when the peroxide of mercury acts in the cold on hydrocyanic acid, the oxygen of the first combines with the hydrogen of the second, which by this last is reduced to its radical. We ought, therefore, to obtain, not hydro-cyanate of mercury, but cyanuret of mercury. Common prussiate of mercury, which is exactly the same, must likewise bear the same name.

The red oxide of mercury absorbing hydro-cyanic vapour with so much facility, I point it out as very proper to separate it from most of the gases with which it may be mixed. I have used it several times with success.

From these few experiments, we see that the oxides produce different effects on hydro-cyanic vapour. Those in which the oxygen is strongly condensed disengage the hydrogen, and form cyanurets of the oxide; but the oxides in which the oxygen is weakly condensed act upon it in so many ways that they require to be more accurately examined than I have done to obtain any general results. (To be continued.)

ARTICLE V.

Meteorological Table: extracted from the Register kept at RoseBank, Perth. Latitude, 56° 25'. Elevation, 130 feet. By a Young Gentleman of the Perth Academy.

THE last column of the annexed table (Pl. XLVIII.) contains, under the head Thermometer, the mean temperature of water from a well 25 feet deep, taken three times every month, viz. on the 5th, 15th, and 25th. The extreme temperatures observed were 42.4° on the 5th and 15th of March, and 48.8° on the 25th of October and the 5th of November, being an annual variation of 6·4°. This variation may be easily accounted for on the commonly received theory of the origin of springs, of which it affords in its turn a beautiful illustration. The temperature of the atmosphere reaches its maximum about the end of July, and its minimum about the end of January. But as the influence of the sun's rays in the one case, and the intensity of the frost in the other, cannot be supposed to penetrate to such a depth as directly to affect the temperature of water 25 feet below the surface, the change in that temperature as indicated in the table must have taken place at or near the surface of the ground. This leads naturally and directly to the true theory of springs and wells, viz. that the water which is deposited on the higher grounds from the atmosphere descends through the earth as in a filter, till, being arrested by an impermeable stratum, it flews along the surface of that stratum, and either bursts out in springs, or is intercepted by pits dug for the purpose; and this theory being admitted, it is easy to deduce from it the law of variation in the temperature of pump water. The rain and melted snow of winter, being cooled down on their first entering the ground, far below the mean temperature of the interior of the globe, successively abstract from the strata through which they pass a portion of caloric; and though, from the quantity of water bearing so small a proportion to the body of earth through which it passes, that body cannot be re

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