to pieces with a hammer; when the lime is sufficiently diluted, it is left in that state for three hours, that the whole of it may be quite dissolved; then mix with it gradually the river pebbles, the iron-dross, the tiles, and the sand ; beat up the mortar for about half an hour, that not a single siliceous stone, or fragment of tile, not perfectly incorporated, may remain *.

Such is the manner in which I prepare the cement : there are two methods of employing it either above or below the brick pavement; both have answered very well; the former appears the most solid the first year, whilst the other suffers the rain water to filter through; but in a certain time it acquires the most perfect sohdity.

As the lime destroys the wood on which mortar is laid, if a terrace is intended to be made on a flooring, the brickwork must be laid in a mortar of earth and sand; when dry, another floor of brick is laid with a mortar composed of lime and sand; it is not necessary that the bricks should be cut but their surface should be rough or cut with the chisel; a sufficient declivity should be given to this pavement for the water to drain off.

In the month of July, when the two pavements are perfectly dry, the cement is made, and care must be taken to work and cut it with the edge of the trowel.

The cement is then collected with the trowel, the back of which is wetted a little; the surface of the cement is again compressed in order to cover the coarser particles, and to make it smooth; when one square is finished, proceed to the second, paying attention to join the two sides well that they may not separate.

* When the cement is almost completed, throw upon it pulverized quick-lime, in quantity about a bushel; the mortar then becomes very difficult to beat up, when a quart or two of whiting must be added, which penetrates and cements all its particles.

The

The cement soon dries, and in an hour's time is capable of bearing a considerable pressure. In seven or eight hours the surface of the cement must be slightly wetted, pressed down with smooth flint stones, and rubbed as if you were polishing marble; this last precaution is essential, and the solidity of the cement depends upon the care with which the operation is performed; the cement being thus composed, its adhesion increases, and its pores are less numerous and more contracted.

In order that the cement may succeed perfectly well in the method described above, it must be applied in portions of two feet square; two workinen are sufficient; the thickness of this coating of cement must be from two in ches and a half to three inches; the surface of the bricks upon which it is laid should be wetted with whiting, and the cement pressed with force against the pavement with the trowel. This must be done during the month of July, that there may be time for the exhalation of the superabundant water in the composition, and that it may be perfectly dry before the rains of autumn.

At the end of August boil a quantity of pitch, of the same kind that is used for ships, and spread it in a liquid state over the cement, with rags fastened to the end of long sticks.

This covering, from its viscous quality, would render the terrace unserviceable during the summer, if the following process were not employed to correct it.

Take unslaked lime, reduced to a fine powder, throw it upon the pitch and with a birch broom sweep off all that does not adhere to the pitch; this lime combines with the pitch, and forms with it a very thin coating of a cement resembling the malta of the Ronians.

At the beginning of October a fresh coating of pitch and lime is applied.

The second method of employing the cement is to lay it immediately upon the first pavement of brick, and to cover it with the second pavement bedded in a mortar of lime and sand.

I have two terraces fifteen toises in length and one and a half wide, and they appear to me to possess the utmost solidity; they have not the beauty of those where the cement covers the brick-work, but they are capable of bearing any pressure or friction whatever.

After having laid the first pavement in a mortar of earth and sand, a layer of cement four inches thick is spread upon it. This cement must have been well worked, and pebbles added to it, rather larger than those employed in the process above described, and the quantity of lime must be proportionably increased. The cement should be then beat down with stampers such as paviors use, and left to dry for a month, when the surface should be wetted with whiting, and the bricks laid with good mortar made of lime and sand.

These bricks must not be broken or cut: I have remarked that by taking off the external surface of bricks which is semi-vitrified, you deprive them of all their solidity; there is then left only an earthy surface, which is soon penetrated by moisture, and easily destroyed by frost.

Care must be taken to fill up the interstices with good mortar, which must be pressed down, and polished with the trowel, and carefully covered with pitch.

Terraces made in this manner suffer water to filter through in small quantity for some time; this water, charged with calcareous particles, stops the pores of the cement; the filtration ceases, and these terraces possess the greatest solidity, and their construction is less expensive.

This cement may be employed with advantage in the interior of apartments, it may be substituted for brick floors, and costs but two thirds of the price.

It is spread upon a flooring of bricks made rough, or cut with any instrument to the depth of an inch or nine lines; instead of pebbles, it is composed of tiles and iron-dross broken into coarse pieces; it is pressed down and polished with smooth stones, but before it is painted it must be left to dry for a month. It may then be painted, and treated exactly like brick work.

Such are the details relative to the composition of the cement which I have employed, and which has perfectly succeeded with me. But, I repeat it, the quantities which I have mentioned must be varied in proportion to the greater or less purity of the lime, and the other materials employed; and the use of pitch is indispensable to prevent the filtration of the water, and the destruction of the cement by frost.

On the Extraction of Spirits from Potatoes. By M. BERTRAND, Apothecary of the Hospital of Instruction at Metz.

From the BIBLIOTHEQUE PHYSICO-ECONOMIQUE.

IN the year 3 (1795), when the utility of potatoes be

came a subject of general discussion, and when that utility was so ably demonstrated by M. Parmentier, scarcely any notice was taken of the spirit that may bè obtained from that root.

Indeed, as the potatoe after boiling appears to have no saccharine flavour, it could not afford room for observations of that nature; it has not the sweet taste of beetfoot, or carrots,; it was not therefore likely to be pre

sumed

sumed that it could yield a sufficient quantity of spirit to defray the expenses necessary for extracting it.

M. Poullmair, starch-maker of Metz, nevertheless succeeded in this point; but in ci-devant French Lorraine, at Sarre-libre, this operation is practised on an extensive scale.

The raw potatoe is hard, acrid, and disagreeable to the taste; it contains a kind of acrimonious principle, of which boiling does not deprive it. If boiled in sınall quantities in steam, it acquires a sweet mixed with an acrid flavour. If eaten without seasoning, the palate is soon palled, and salt must be used for correcting this taste.

The action of heat, by developing a slight tendency to saccharine fermentation in the potatoe, does not dispose it to yield a spirit in considerable quantity. The action of caloric disengages a great quantity of water, renders the root farinaceous, its skin is more or less cracked, and even peeled off when the potatoe is very flowery, Its substance appears like an aggregation of small detached particles, without any regular form, amongst which are discovered small shining bodies, which can only belong to the starchy fecula, of which they are the appropriate characteristic. It is easily reduced between the fingers into a friable substance, the particles of which appear to resist slight pressure on account of the mucilage and humidity which keeps them combined.

It is necessary to add a saccharine substance, a ferment of some kind, to facilitate the fermentation of the mucilage and starch which compose the principal part of the potatoe. Sugar, melasses, and honey would prove important resources, but only barley and beer-wort are employed,

The process is as follows.-Take 600 lbs. of potatoes, which in common years are sold for 1 fr. 50 c. but in the

year