ourselves, by placing the transverse section of a carbonized branch under the microscope. We discover every little cell of the plant, and we may assure ourselves that the form of the partitions have remained intact.

1

2400

The cells of wood charcoal have, as a medium, a diameter of of an inch; their surface would be equal, therefore, to 100 square feet, if the charcoal itself occupied no space. I prepared some wood charcoal, which weighed .9565 grains, and after boiling it some time in pure water, and wiping simply the surface of it, its weight was 2.2585 grains; its weight under water was .110 grains; the space into which the water had penetrated, and, consequently, into which elastic fluid might have penetrated after the expulsion of the latter, constituted then of the total volume of the charcoal; in reckoning the space occupied by the charcoal itself, we find that the extent of its surface is only 73 square feet. De Saussure found that wood charcoal absorbs 35 times its volume of carbonic acid at the temperature of 12 degrees, and under a pressure of 26.895; but 35 volumes of carbonic acid is found in a space which constitutes ths of the total volume of the charcoal, and, consequently, 56 times smaller than the space originally occupied by the carbonic acid.

Agreeably to the experiments of Addami, carbonic acid is liquified under a pressure of 36.7 atmospheres, at a temperature of 12 degrees. We are thence led to conclude that more than one-third of the carbonic acid which is condensed in the pores of the charcoal, is in a liquid state on the sides of the cells.

If 35 cubic inches of carbonic acid are condensed on a surface of 73 square feet, or 10,512 square inches, the thickness of the layer of liquid carbonic acid on the sides of the cells must be .000002 of an inch. This stratum is thicker when the experiment is made with ammoniacal gas, chlorhydric acid, or sulphurous acid, which do not require so enormous a pressure for liquefaction, and which are absorbed in more considerable quantities. Since all porous bodies, in presenting to the gas a considerable surface, act in the same manner as charcoal, we must admit that the gases which are in contact with solid bodies are in a peculiar state, and different from that in which they are when isolated from them; and moreover since the thickness of the layer of condensed gas varies, attraction is exerted not only on the gas which is in immediate contact with the solid body; it acts at variable distances. But porous bodies do not act at their surface only, for if it were so, the absorption of different gases by different substances ought to be in the same proportion. It is not thus, since, according to Saussure, wood condenses proportionally more carbonic acid than charcoal; also asbestos, spongy quartz, cotton, and silk tissues absorb different gases in proportions varying from that of wood charcoal.

The absorbent power of pulverulent substances has been hitherto but very little studied. Platina black, prepared by the method of Davy, far surpasses all others: 10 grains condense .550 cubic inch of oxygen; that is to say, one cubic inch of it would condense 253.440 cubic inches, (Chimie de Platina, by Dobereiner, page 64;) but it is

impossible to decide what the volume is which platina takes up when it condenses oxygen, because it is in a state of powder. The property which certain bodies possess, like silex, of condensing the humidity of the air, authorizes us to conclude that they have an aptitude in condensing gases.

As solids attract gases, they are capable, in like manner, of exerting this attraction over solid bodies; thus we may, by means of charcoal, deprive alcohol of the potatoe oil which it holds in solution. In boil. ing charcoal with water, the oil passes, unaltered, to the latter; this force of attraction carries off solid coloring matters from liquids which hold them in solution.

Some precipitates have the property of attracting a portion of the soluble salts from the fluid around them; they entangle and remove them, but washing sets them free.

I dissolved some nitrate of barytes in 10 parts of water; after having precipitated about half of it by sulphuric acid, I determined the quantity of nitrate of barytes which was held by the clear supernatant fluid. The fluid liquid, arising from the washing of the precipitate, was evaporated, and the nitrate of barytes which it contained was determined.

In subtracting the weight of this nitrate, and the weight of the sulphate of barytes obtained from the total weight of the wet precipitate, the weight of the water contained in the liquid was arrived at. In calculating, from these data, on the one part, the weight of the nitrate of barytes in the liquid which overflowed the sulphate, and on the other part, that of the liquid which moistened the precipitate, it was found that two-thirds only of the latter was dissolved in it, and that the one-third contained in the water used in washing must have been condensed by the attraction exerted by the precipitated sulphate. If, instead of precipitating a solution of barytes, we employ the chloride of barium, the latter is thus drawn away. But if we precipitate a solution of nitrate and sulphate of soda, by nitrate of barytes, and wash the precipitate until a drop of the washing leaves no trace of solid matter on a platina blade, it happens, in this case, that the sulphate of barytes may retain as much as two per cent. of nitrate of soda; to remove it the precipitate must be calcined, and then washed. The sulphate of barytes, therefore, exerts an attraction so weak on the chloride of barium as to be unable to remove it from its aqueous solution; but with respect to the nitrate, the attraction is so strong as to render a great quantity of water necessary to clear it; but water is incapable of removing completely, from sulphate of barytes, the nitrate of soda which it retains at the moment of its formation.

One may very easily judge of the force of attraction which solid. bodies exert upon each other by considering the action of cement upon wood and glass. If we cover a plate of glass with moist bladder, and, when dry, try to detach it, we tear off portions of glass. The action of the bladder upon the glass is stronger, therefore, than the cohesion of molecules of the glass itself; but if we allow the plate of glass and bladder to remain some time in boiling water, the gelatine is dissolved, and the bladder is easily removed.

Although this attraction is very strong, it is less considerable than that of sulphate of barytes for nitrate of soda. The attraction which solid. bodies have for liquids and gases is manifest not only by immediate contact, but also at a determinable distance. We may prove it by using plates of glass, or of quartz, having two perfectly smooth faces. The first is to be suspended, and the other furnished with the means of attaching weights. I deprived two plates, thus disposed, of all adhering humidity; the thinnest layer of it interposed, shows itself by the production of the colored rings of Newton. By compressing these plates afterwards, until the colored rings begin to appear, we may easily determine their distance. At the appearance of the second ring, the lower plate, whose weight was 14 grammes, remained attached to the first. The contiguous surfaces were but one inch square; when pressed together, so that the black appeared over nearly the whole of the first ring, several pounds might be suspended from it. By having this apparatus for some time under the air pump, the plates did not separate, so that atmospheric pressure was not the cause of their adherence.

We know that this kind of attraction takes place generally during the crystalization of bodies. A body dissolved deposites itself on threads, or solid bodies, suspended in the liquid, much quicker than if these are not present. Crystals are formed much faster around a crystal already formed than in any other portion of the liquid, when, for example, the force of the solvent is lessened by a diminution of its temperature. The solvent force of water is, therefore, less energetic near a formed crystal than at a certain distance from it.

In some cases it is easy to account for the chemical combinations which the action of solid bodies on liquids and gases may excite, but in others the explanation becomes more difficult. It is possible that condensation alone may be the cause of it in gaseous bodies. We may, in this way, very well explain the distinction which M. Thenard observed, on introducing charcoal into a mixture of sulphhydric acid. and oxygen. When platina black, which has condensed oxygen, is placed in contact with chlorhydric acid, there results, according to Dobereiner, chloride of platina. We know that, in this case, the condensed oxygen may readily seize the hydrogen of the acid; and yet the affinity of chlorine for platina interferes in the case. The affinity of gold for chlorine provokes the decomposition of nitric acid. by chlorhydric acid, when leaves of gold are placed in aqua regia, since the latter contains free chlorine only after it has been warmed, or after being for a long time left to itself.

When a gas is in the nascent state, a phenomenon is presented analogous to those just mentioned; the gas combines often with a body in contact with it, which, in other circumstances, would produce no action upon it. Thus, in the cases in which the chemical affinity of two gases is weak, it may happen that their condensation causes them chemically to combine.

Nevertheless it appears doubtful whether we ought to attribute the combination of two bodies, which, like oxygen and hydrogen, have so strong an affinity for each other, to the effects of condensation alone,

though we may be authorized to grant that in the various physical conditions of platina a condensation of gas takes place at its surface. We know that in leaf and in fine wire, platina acts as well as in the precipitated, or spongy, state, or in black; but the combination is slower as the surface used is more limited.

The leaves and sponge of platina do not condense a large quantity of oxygen; but in comparing their surfaces with that of platina black, we perceive that it ought to be so. The sponge of platina arising from the decomposition of the double chloride of platina and potassium is formed at a temperature at which the mixture begins to agglomerate, and presents itself under the form of plates, which cannot certainly possess a surface large enough to admit of an easy appreciation of gaseous condensation.

An experiment first made by M. Fusinieri, and is easily repeated, proves that air and moisture are condensed on the surface of glass. If we pour into a glass tube boiled mercury, which has been cooled in a vacuum, we find that it gives out air, when heated, even when the precaution is taken to assure ourselves by the microscope, that no traces of it adhere to the sides of the glass; but if into a tube of glass which has been exposed to a high temperature, we pour mercury by means of a funnel whose point touches the bottom of the tube, and then heat the tube, not a bubble of air escapes, even when mercury is used which has been agitated with air and water, and left to dry by simple exposure to free air. The gaseous bubbles then which the mercury, in the first experiment, yielded, must have come from the air and moisture condensed on the sides of the tube; but the quantity of air and water, thus condensed, is so trifling, its presence can only be proved by such an experiment as above stated.

It would be impossible to prove the condensation of any gas whatever on the surface of platina leaves, even supposing it to be as considerable as that of the carbonic acid on the surface of charcoal.

A mixture of alcohol and oxygen act, in the presence of platina, absolutely in the same manner as a mixture of oxygen and hydrogen. Oxygen is devoid of action on weak, or concentrated, alcohol. Platina black provokes their combination. Other bodies also do the same. It has been thought that to effect this reunion it was necessary to recur to the use of ferments; but M. Duflos has proved that chips of wood, soaked in acetic acid, act in a manner analogous to platina black. One might have supposed that the acetic acid thus used had deposited some ferment on the wood; but these ferments would soon have been decomposed by the oxygen of the air, and M. Duflos has proved that with chips, or shavings, alone, we may transform alcohol into acetic acid for months together.

When acetic acid is prepared by exposing beer, or fermented liquors of this kind, to the action of air, they become turbid, and deposit matters of an organic nature. These spongy matters, acting after the manner of platina black, will condense oxygen, and thus determine the combination of these bodies.

To be Continued.

On a Voluimnimeter. By M. HERMANN KOPP.-Ann. de Chimie, froin Ann. des Mines.

TRANSLATED FOR THE JOURNAL OF THE FRANKLIN INSTITUTE.

I have given this name to a new instrument which may readily serve to determine the volume of any substance, solid, or liquid, and thus furnish the density of various bodies for which the ordinary methods are insufficient.

The instrument is constructed in the following manner:-K, fig. 2, is a pump in which moves a solid piston; this pump communicates below by means of a bent tube p, with a cylinder i i, the upper part of which is closed, and pierced by two tubes cd, and iq. The straight tube c d, open at both ends, is prolonged upwards, and fitted with an arbitrary scale, the zero of which is at a short distance from the cylinder. The tube i q, bent as in the figure, enters the bottom of the cylindrical vessel r, the vertical parts of which are represented in fig. 3. At the upper part of the same cylinder i, i, are fixed several platina points a b,. . . . of different lengths.

m

Fig. 3.

m

Fig. 2.

20

m

The vessel r, contains another vessel w, in which is placed the body to be subjected to the experiment, A disk mm, compressed by means of a screw t, and of an elastic body u, hermetically closes the vessel r, the borders of which are worked for this purpose. The pump K, the tube p, and the lower part of the cylinder i i, are to be filled with mercury.

Thus arranged, let x, be the volume of air enclosed in the cylinder ii, commencing at c, in the vessel r, and in the tube of communication iq. Let y, be the quantity by which the volume will be diminished by lowering the piston so as to bring the mercury in contact with the point a, and let B, be the common height of the barometer, we shall have, for the height of the column of mercury in c d, y B, the measurable height, and which I will suppose equal to

Xx

1

y

B; n, having been accurately determined, once for all, for the same

If now we introduce into the capsule n, a body of known volume z, and compress it to the extent of the volume y, we shall have, in designating by h B, the new height of the column of mercury in the tube c, d :