The Romans regulated with great care the preparation which should be given to mortar before it was employed *; and M. Delafaye has pointed out many mortars proper for the formation of these bricks, or factitious stones; as, for example, one measure of lime, slacked dry, and three measures of pounded stone, sifted, to which add the necessary quantity of water, and work the whole well up together; or, secondly, one measure of fine dry sand, free from clay, one measure of sifted stone-powder, and one of dry slacked lime, with just water enough to make them unite, and the whole then well worked together. Thirdly, five parts of rough sharp sand, two parts of fresh burnt dry slacked lime, with just water enough to render it adhesive, but no more. Fourthly, one measure of dry pulverized clay, kneaded with oil, eight measures of fine clean sand, or of pulverised and sifted stone, or of the two combined, and two measures of recent quick-lime, moisten the eight measures of sand or stone, and work them up like soft mortar, bruise the lime fine, and add it thereto with a trowel or pestle, knead it well up together, adding water if necessary to render the whole adhesive, but no more than is requisite for this purpose; when perfectly mixed, and and whilst yet warm from the slacking of the lime, add the clay which was kneaded with the oil, and beat them till thoroughly incorporated. This mortar must be quickly used, as it will speedily set, and become impervious to

moisture.

In Piedmont, factitious stones are made, which they call prisms, from the form given to them, which is that of

r

* In lately removing the foundations of Burleigh House, latterly Exete 'Change, the labourers frequently encountered those of a more ancient structure, most probably Roman, as the bricks composing them were much smaller than those used in the building of Burleigh House, and were of a red colour. The mortar also had coarse grains of a white substance incorporated with it, as though the quick-lime used had never been slacked, but only coarsely powdered when forming the mortar. The consequence was, that it cost the labourers infinite time and trouble to break up these foundations with their pick-axes, as was very frequently witnessed by the Editor, from the windows of his apartments opposite to them; and also that they broke up bricks and mortar in masses mingled together, the mortar and the bricks being both equally hard.--EDITOR.

VOL. VI.

a triangular prism, as they are principally intended for the projecting angles of walls. They use an excellent aquadurant lime, which is slacked in the usual way, and left for four or five days to complete the process; it is then placed in the centre of a hollowed heap of sand, unequal in grains from the ordinary size, to that of coarse gravel; the whole is then carefully mixed. A triangular trench, of indefinite length, is prepared in a situation free from the risk of inundation, the sides of which are carefully smoothed by the aid of a trowel and some water. The prism is then formed by successive beds of the mortar, and pebbles of uniform size, equally distributed. The prism is then covered with the earth which had been dug out, to the thickness of nearly a foot. The proportions of the ingredients used, are about fourteen parts of lime in a pasty state, ninety parts of the unequal grained sand, and twenty of the pebbles. These prisms commonly lie buried for three years, at the end of this time they will bear very heavy loads, and when let fall upon each other, from a height of twenty feet, or upwards, they may be chipped at the corners, but will not be broken.

From the ordinary kind of lime, good small bricks of this description may undoubtedly be made; but for factitious stones of large size, those limes must be used which solidify quickly; as the magnesian lime and puzzolana of Italy, Parker's Roman cement, and the other hydraulic limes of England. Moulds of the various forms may be made, and the artificial stones may be also consolidated, by beating and pressure, while yet partially moist.

Delafaye is of opinion, that to the numerous other proofs of the ancients having made large artificial stones for many of their edifices, the great Egyptian pyramids may be added. The stones which form the facings of these structures, he unhesitatingly declares to be of this kind. They have all the same dimensions, and are about thirty feet long, four broad, and three in height. They have no connecting cement, and fit so closely, that the blade of a

knife cannot be inserted between them. A fragment, when sawn or broken, perfectly resembles factitious stones, being without any binder, such as usually appears in the naturally compounded stones. A fragment of a similar stone, which was taken from the ancient buildings of Alexandria, contained a piece of brick, which had evidently been burnt in the furnace. There is no quarry,

within a great distance, from which the stones could have been obtained; and it is also thought, that their weight, about 65,000 lbs. each, is so immense, as to render it highly improbable that they could have been transported, and afterwards raised to a great height.

Several other reasons are urged, to prove the correctness of the opinion, that these, and other large masses of stone, are factitious. In more modern buildings, it is declared that artificial stone has been employed; the pillars of the church of St. Amand, in Flanders, and the columns of that of Vezelai, in Burgundy, are, it is said, acknowledged to be of this kind.

We shall not introduce the reasoning of those who deny or controvert the opinion of the factitious character of these stones, as we have now nothing to do with this controversy; our only object being to show that such stones were probably made by the ancients; and that certainly we have the materials, and are acquainted with the processes by which they may be formed. These materials are various, and require to be differently treated. Those which set slowly, may be consolidated and improved, by beating and pressure; those which set quickly, like Parker's Roman cement, and some others, must be allowed to do so undisturbed. Some kinds should be permitted to consolidate when shut up in a damp situation, or covered up in the ground. Experience and observation, in fact, must determine the best mode of procedure in each particular

case.

Note. We have transcribed this Article from "The Franklin Journal." The Editor, Dr. Thomas P. Jones

having abstracted it chiefly from M. Hassenfratz's paper on the subject.

X.-On the Progress of Inventions connected with Navigable Canals.

(Continued from Vot. V. page 189.)

THERE is a great variety in the size of locks, as the canal is navigated by large or small boats. The sea-lock, near Inverness, on the Caledonian canal, is 180 feet long, forty feet wide, and twenty feet deep, besides the lift, or difference of the levels, of eight feet. The locks on the Derby canal are ninety feet long, fifteen feet wide, and eleven feet deep, including the lift of eight feet. Those on the Leeds and Liverpool canal are seventy feet long, fifteen feet wide, with nine feet lifts. In passing a lock, every ascending boat requires a quantity of water just sufficient to fill the lock from one level to the other, together with a quantity equal to the weight of the boat. But a descending boat expels a quantity of water in the upper canal as it enters the lock, which is retained by the upper gates, equal to the weight of the boat and its lading. To make a double passage then, or for two boats, equally loaded, to pass in opposite directions, it requires a quantity of water equal to the area of the lock, multiplied by double the lift. This may, perhaps, be taken without any great error, on locks of medium size, at 320 tons. A necessary precaution in fixing the sites of locks, is to avoid placing them too near together, for in such case, the water let out of the upper lock, on the passage of a boat, will overflow the banks of the subjacent level, and not only be lost, but injure the works. The locks should be all of equal height, so that the water used at the upper lock, or an equal quantity, may serve for the passage of the boats through the lower lifts.

A great many contrivances have been proposed, either as improvements of the common lock, or a substitute for it.

If in a lock of the common construction, we consider the water which is let down from one level to another, in the light of a force expended to produce a given effect, which is the elevation or depression of the boat and its load, there is a loss of the acting force, unknown in any other mechanical operation. Thus, to raise a boat and load, weighing thirty tons, through eight feet, it will in general require 180 tons of water, falling through an equal space. But in descending boats the effect is negative, and [the disparity between this and the force is yet more striking. If, therefore, in transferring boats from one level to another, the economy of force only were considered, the inclined plane, arranged as it is in England, must be very advantageous, the expence of force being, in theory, merely the small quantity required to overcome the friction of the machinery, and the inertia of the moving masses.

Mr. Fulton, who paid much attention to this subject in the early part of his life, says, "I do not hesitate to prognosticate the annihilation of lock canals by improved science, in like manner as improvements in machinery render the old apparatus useless.' (Fulton on Canals, page 28.) A bold prediction, which seems yet very far from being fulfilled. This gentleman was then very highly in favour of the inclined plane as a substitute, not only for locks, but for aqueducts. In his work, published in London, in 1796, he has detailed fully his plans. His machinery, besides the inclined plane, may be described in general terms, as consisting of an endless chain, running over wheels, fixed, one at the top, and one at the bottom of the plane; to this chain are to be attached two boats, in such a manner, that the descending boat assists in dragging up the ascending one. The small force which may be necessary to pass the boats so arranged over the plane, is to be supplied by a vessel of water, descending through a shaft from the upper canal. The boats are to be small, and they are to be provided with wheels, to diminish the friction in passing over the planes. Various other modifications of the inclined plane have been proposed;