on all sides, is a proposition that is not so obvious, but it is what is here attempted to be demonstrated; and not only that the forces are different, but that these bodies are forced together with a force inversely as the square of their distances, and directly as the masses; thereby according with all the laws which are attributed to gravitation.

Let A B represent a globe with a hollow vacant space within it, then there would be a compressing force from the atmosphere of about sixteen pounds upon every square inch

But this

of surface, tending to compress it to the centre,
which is supposed to be a vacuum.
compressing force would continue to press on
the exterior surface of this globe, however A
much diminished the interior vacuum was made,
or till there was no vacuum. Thus the pres-
sure upon the solid globe is seen to be the same
as upon one which is exhausted, of whatever
size the exterior be, while the exterior is unaltered.

All this will readily be granted: but suppose now that a small hole E F, was made from the exterior to the interior space, and a communication made from the atmosphere to the vacuum within the globe, the elastic atmosphere would rush in immediately, and exert a force by its elasticity on the interior hollow surface equal to sixteen pounds upon the square inch, the same as on the outside surface. This, I conclude, will also be granted as a truth: but it is evident that, as the outside and inside surfaces are to each other as the squares of the outside and inside diameters, therefore the pressure inward to the pressure outward would be as the outside surface to the inside surface, and in all cases will be proportional to the squares of the diameters. Thus, were the internal diameter two feet, and the outside diameter three feet, then the pressure inward to the pressure outward would be as the square of two to the square of three, or as nine to four.

From this it follows as a corollary, that any hollow globe of soft compressible matter would be pressed together, if the consistency of the materials were not such as to withstand it; and that all hollow inelastic vessels have a greater force pressing them inwards than outwards, when they possess any considerable thickness of material. It is not true, therefore, that the parts of a hollow globe are pressed with the same amount of force from the centre as to the centre; but in a ratio as the squares of the inside to the outside diameter, or as the surfaces to each other.

Let the hollow globe now be supposed to be formed of frustums of pyramids, all pointing to the centre, as shown in the figure. The pressure inward on each of the frustums, to the pressure outwards, would still be as the outside surface of the base of each to the surface of its small end; and these are still as the square of the outside diameter to the square of the inside diameter.

This conclusion, it is supposed, will also be readily granted, there being no alteration in the figure, and the base of each pyramid being to its top as the whole outside to the whole inside surface.

Suppose farther, that one of the frustrums were abstracted; this only widens the communication between the external atmosphere and internal space, still the same proposition would hold with regard to the external and internal forces operating on the remaining frustums. In the same way let all the remaining frustums but the two opposite ones be abstracted from the globe, as in this figure, still the same ratio will hold with these; the pressure inward to the centre from the outside, will be to the pressure from the centre outwards, as the outside surface to the inside surface of the frustums, or as the square of the outside diameter to the square of the inside dia

meter.

A

E

B

Were these two bodies globes, or any other form, there is no reason why the same law should not hold good with regard to them.

It is evident that as the inside diameter or surface approaches the outside, that the shell of the globe gets thinner; and when the surfaces coincide, then the inside force or pressure is just equal to the outside pressure, and then they will balance each other, but not till then.

It is also evident that the greater the distance between the bodies A and B, or the farther they are from the centre, c, that the less will be the difference between the exterior and interior surfaces, and that this will be inversely as the square of the distance between the bodies, or which is the same, from the centre c.

It is also evident, that the larger the mass when the distance is the same, the greater must be the exterior pressure over the interior; because the greater is the difference between ends of the frustums of the pyramids, or the greater is the angle which each body subtends at the other, or at the centre c.

We have thus arrived at the same conclusion with regard to the laws of forces by which matter is governed, as the Newtonian theory of attraction or gravitation requires; namely, that the power of the forces by which bodies are made to approach each other, are inversely as the squares of their distances, and directly as their mass, or quantities of matter; and this, by only supposing the existence of an elastic compressing medium extending throughout space, which is now admitted by many of the philosophic world to exist.

This pressure to a centre between bodies must necessarily exist if this is a correct demonstration: it flows from the nature of a compressing elastic fluid and hence there would be no necessity for attraction, for both cannot have place. If the forces, which I have attempted to show, have actually a place, then that of attraction can

have no place, as the former is capable of accounting for all the phenomena upon a much more intelligible and rational principle than the latter.

Theory of Saponification.*

AWARE of the importance of investigating the theories involved in the chemical arts, with a view to their ultimate improvement on scientific principles, we had formed the design of embodying the later observations of chemists on the oily substances, when an essay of Professor Liebig's appeared in the "Annalen der Chemie und Pharmacie," for March, 1841, which contains an excellent view of the theory of saponification; we therefore translate the essay nearly entire. J. C. B. and M. H. B.

What was known of the nature of saponification previous to the commencement of the present century, amounted to nothing, excepting the important discovery, by Scheele, of the sugar of fats, now called the hydrated oxide of glyceryl (glycerule). Chevreul began in 1813, a series of investigations on soaps, which have not only thrown a clear light on this portion of chemistry, but have also led the way to the most brilliant discoveries in the whole province of organic chemistry. We are indebted to him for the present predominating principle in all organic researches, viz. to subject a body to a series of changes, and to ground its composition on the ascertained connexion of these changes.

Chevreul proved that all fats comprehended under the terms grease, oil, and tallow, consist of three materials united in the most varied proportions, one of which, oleine, at common temperatures, and below 32° Fahr., is always fluid, the others solid, the one called stearine, the other margarine; distinguished from each other by their melting points, and the different acids they give rise to by decomposition. These fatty substances are each composed of a peculiar fat acid, united to a compound oxide, the oxide of glyceryl, and being salts, are subject to decomposition like ordinary salts.

Decomposition ensues when a fat, i.e., a compound of oxide of glyceryl, is treated with an alkali, or with oxide of lead or zinc ; the alcalies, or metallic oxide, combining with the fat acid; the former constituting soluble salts, or soap, the latter insoluble salts, or plasters. The oxide of glyceryl, at the moment of its separation from the fat acids, takes up water and forms hydrated oxide of glyceryl.

The weight of the hydrate of glyceryl, added to that of the hydrated fat acids, amounts to more than the weight of the fat employed; the increased weight arising from the water entering into combination with the glyceryl and fat acids.

In the saponification of fats by alcalies, no other products are formed, and the operation is conducted equally well in vacuo, or in

• "Journal of the Franklin Institute."

the air. With strong alcaline lyes, the soap separates from the concentrated fluid, and collects on its surface, while the glyceryl remains dissolved in the alcaline solution. The soap remains dissolved in a weak and hot alcaline lye, but on cooling, the whole congeals to a gelatinous, translucent mass.

Soaps are solid and hard, or soft. The last are obtained from drying oils, and contain potassa as a base, and to give them more consistence, tallow and fat oils are added, which form solid soaps. The hard soaps contain soda, and are prepared with fat oils, tallow, &c.

Soda soaps are made in England and France directly by soda and fats, in Germany by decomposing potash soaps with chloride of sodium. Commercial soaps from vegetable fats consist of oleated and margarated alcalies; those from animal fats are salts of stearic, margaric and oleic acids, with an alcaline base.

Potassa and soda soaps are readily soluble in hot water and alcohol; the addition of a quantity of water to the aqueous solution produces a precipitation, the neutral salts of stearic and margaric acid, decomposing into free alcali, which remains in solution, and acid steorate and margarate of alcali, which precipitates in form of pearly, crystalline scales.

Potassa soaps are more soluble in water than those containing soda. Stearate of soda may be regarded as the type of hard soaps, and when in contact with ten times as much water it suffers no striking change. Stearate of potassa forms a thick paste with the same quantity of water. Oleate of soda is soluble in ten parts of water; the oleate of potassa dissolves in four parts, and forms a jelly with two parts, and possesses such a strong affinity for water, that 100 parts absorb 162 in a moist atmosphere. Margaric acid acts similarly to stearic. It follows from this that soaps are soft in proportion to the oleates, and hard in proportion to the stearates and margarates they contain. Soda soap exhibits a peculiar behaviour to a solution of common salt; it loses the power of being penetrated by, or dissolving in, a solution of salt of a certain strength, and this remarkable action is an important condition in its manufacture, on which depends the separation of all free alcali and oxyde of glyceryl, its content of water, and the state in which it is brought into the market.

If a piece of common hard soap, cut into pieces, be put into a saturated solution of salt, at ordinary temperatures, it swims upon the surface without being moistened, and if heated to boiling, it separates without foam into gelatinous floccula, which collect on the surface, and upon cooling unite into a solid mass, from which the solution flows off, like water from fat. If the flocculæ be taken out of the hot fluid they congeal on cooling into an opaque mass, which may be pressed between the fingers into fine lamina without adhering to them. If the solution be not quite saturated, the soap then takes up a certain quantity of water, and the flocculæ separate through the fluid in boiling. But even when the water contains of common salt, boiling produces no solution.

If the soap be boiled in a dilute and alcaline solution of salt, and suffered to cool, it again collects on the fluid in a more or less solid state, depending on the greater or less concentration of the solution, i.e., on the quantity of water taken up by the soap. By boiling the dilute salt solution with soap for a considerable time, the watery flocculæ swell up, and the mixture assumes a foaming appearance; but still they are not dissolved, for the solution separates from them. The flocculæ, however, have become soft and pasty, even after cooling, and their clamminess depends more or less upon the quantity of water they have taken up. By still continued boiling this character again changes, and in proportion as the water evaporating renders the solution more concentrated, the latter again extracts the water from the flocculæ ; the liquid continues to foam, but the bubbles are larger. At length a point is attained when the solution becomes saturated; before this, large, iridescent bubbles are observed to form, and in a short time all foam disappears; the liquid continues boiling without foam, all the soap collects in a translucent mass on the surface, and now the solution and soap cease to attract water from each other. If the plastic soap be now removed and cooled, while the solution is pressed out, it has become so solid as scarcely to receive an impression from the fingers. In this state it is called grainsoap (Kernseife).

The addition of salt, or its solution, or a concentrated alcaline solution of soap in water, precipitates the soap in gelatinous flocculæ, and the mixture behaves precisely like solid soap boiled with a dilute solution of salt. Carbonated and caustic potassa act exactly like salt, by separating soap from the alcaline fluid, in which it is absolutely insoluble.

The application of the above to the manufacture of soap is evident. The fat is kept boiling by au alcaline lye until all pasty matter disappears, but the lye should only have a certain strength, so that the soap may be perfectly dissolved in it. Thus tallow may be boiled for days in a caustic potass-lye, of sp. gr. 1-25, without saponifying; if the lye be stronger, a partial saponification takes place, but being insoluble in the fluid, it floats upon the surface in a solid mass; by the gradual addition of water and continued boiling, at a certain point the mass suddenly becomes thick and clammy, and with more water a kind of emulsion is formed (Seifenleim), which continued heating renders perfectly clear and transparent, if a sufficient quantity of alcali be present. In this state it may be drawn into long threads, which, on cooling, either remain transparent, or are more milky and gelatinous. As long as the hot mass suffered to drop from a spatula exhibits a cloudiness or opalescence, the boiling is continued or more alcali added. When excess of alcali is present, the cloudiness arises from imperfect saponification or want of water; the former is shown by dissolving a little in pure water, which becomes perfectly clear when the whole is saponified; if the lye contain lime, the mixture is also clouded, but the addition of carborated alcali instantly clarifies it.