not hitherto employed. Thus, in operating by the dry method, as is generally the case, instead of calcining the lime-stone or lime with sand and clay, the inventor, in order to facilitate the combination of the silica and alumina with the lime, introduces a small quantity of potash or soda, in the state of carbonate, sulphate, or chloride, or of any other salt of these bases, susceptible of decomposition, or becoming a silicate, when such calcination takes place. The salt of potash or soda, the quantity of which varies from three to six per cent. to the quantity of lime, is employed in the state of solution, so as to penetrate and mix better with the alkaline salt in the chalk or slacked lime. Calcination effects the rest, in the ordinary manner.

In order to combine or incorporate more equally, by the dry method, the alumina, and the oxides of manganese, and of iron, with the lime, the sulphates of these bases are first decomposed by the slacked lime, by making a paste with a solution of the sulphates, mixed with the lime. This paste, into which the sulphates in question enter, in the proportion of from six to ten per cent. of the lime, is then calcined, in order to produce an hydraulic lime. All sorts of lime are made hydraulic, by the humid method, by mixing slacked lime with solutions of alum or sulphates of alumina; but the best method consists in employing a solution of the silicates of potash, or of soda, called liquor of flints or soluble glass. An hydraulic cement may also be made,

which will serve for the manufacture of architectural ornaments, by making a paste of pulverized chalk, and a solution of the silicate of potash, or of soda: in working with this plaster, it becomes much harder than ordinary plaster.

These same silicates of potash or soda, dissolved in water, will also harden chalk, or soft and porous stones, and transform them, artificially, into hard stones. In order to do this, these soft stones, either rough, or cut into their proper forms, must be soaked in a solution of the silicate, either warm or cold, and allowed to remain there a longer or shorter time, according to the degree of hardness which it may be necessary to give them; after which, they must be taken out and left exposed to the air. At the end of a

few days, stones, thus prepared, will have acquired a hardness equal to that of marble; and this quality, in a little time, pervades the whole mass; for if, for the purpose of polishing, the outer coat or surface be removed, the inner one, which at first is not so hard, will harden in its turn, by exposure to the air. This takes place as far as the silicate has been able to penetrate. A more superficial hardness is obtained, by applying the solution of the silicate of potash or soda, by means of a brush. It is in this manner that walls, constructed of chalk and mortar, may be hardened. Sculpture, and various other objects, which may be made or prepared in chalk, may be hardened, and afterwards serve for decorating buildings, and other purposes, without the fear of their becoming injured by frost or damp. Chalk, hardened in this manner, may also be used as a substitute for the stones now employed by lithographers. Plaster models may also be hardened, by placing them, for some time, in a solution of the silicate; but it would be still better to add a portion of the solution to the paste, at the time of making the model, or using the plaster. The silicate of potash or soda is prepared by fusing one part of white siliceous matter with from one and a half to two parts of potash or soda, in the ordinary reverberatory furnaces, or in a glass-maker's or iron crucible. The solutions may be used of any density for plaster; but they should be weaker for chalk. In the last place, the inventor has found that the silicates of potash or soda, when dissolved in water, decompose spontaneously in the air, and cover the objects, to which their solution has been applied, with a strong covering or layer; therefore, by applying the solution of silicate of potash, or of soda, to polished iron, and allowing it to dry in the air, the metal is preserved from oxidation. By soaking wood many times in this solution, and allowing it to dry in the open air, every time after it has been placed therein, it becomes so much penetrated with silica, that it acquires a considerable density and degree of indestructibility.

The solution of the silicate of potash is not the only substance which, by being injected into porous bodies, tends

to harden them. A mixture, made from a solution of bicarbonate of ammonia, and of chloride of magnesium, may be successfully employed; or a mixture of the solutions of ammonia and chloride of calcium may be used. In these latter cases, instead of having siliceous injections, they are either magnesian or calcareous. Soft and porous stones may also be considerably hardened, and defended from the action of damp, by first well drying them, and then dipping or steeping them in sulphur, or some natural or artificial resinous or bituminous substance, rendered liquid by heat.

The patentee claims, Firstly, the application of certain new means, to change or convert all descriptions of lime into hydraulic limes and cements, or such as become hard under water, or when exposed in damp situations, by combining these limes and cements with silica, alumina, the oxide of manganese, or the oxide of iron, either by the dry or humid method. Secondly, the manufacture of hard artificial stones from chalk, plaster, and all porous stones in general, by injecting into them, or imbuing them with silica, or the carbonates of magnesia or lime, by any of the above-described processes; or by causing them, by virtue of their porous nature, to absorb either melted sulphur, or bituminous, resinous, or fatty matters, properly liquified by means of heat. Thirdly,-in the employment of the silicates of potash or soda, for making or forming a stony plaster or coating upon a variety of substances; thereby preventing iron from becoming rusty or oxidized, and rendering wood and other organic matters harder, and not liable to decay.—[Inrolled in the Petty Bag Office, September, 1841.]

Specification drawn by Messrs. Newton and Son.

To EDWARD PALMER, of Newgate-street, in the city of London, philosophical instrument maker, for improvements in producing printing or embossing surfaces.-[Sealed 15th January, 1842.]

THE first part of these improvements consists in obtaining

printing surfaces, in relief, by means of the electrotype process, or by casting; the subject being, in the first place, engraved or etched, through a white or light-colored composition, upon a black or darkened plate, and from it the printing surface is produced.

The plate, just mentioned, on which the etching ground is laid, is made of metal, (by preference of German silver or copper,) and its surface is blackened or darkened, by immersion in a weak solution of chloride of platinum, or hydrosulphuret of ammonia, or by any other suitable means. It is then covered with a layer of white or light-colored composition, of the same thickness or depth as the intended relief of the printing surface. The composition is formed by mixing together, with the aid of heat, one ounce of the clear part of Burgundy pitch, one ounce of resin, two ounces of white wax, and one ounce of spermaceti; but the patentee does not confine himself to these ingredients, as others might be used with equal advantage.

When the plate is cold, a small quantity of finely pulverized sulphate of lead is dusted over the surface of the composition, and rubbed gently in with a piece of soft linen; the composition is then exposed to a gentle heat, in order that the sulphate of lead may sink into it; and this process is repeated until the composition has become sufficiently white. The subject may now be engraved or etched in, by cutting through the white composition to the blackened surface of the plate, which, appearing at those parts that are cut away, will produce a representation of the subject, similar to the impressions from the printing surface (afterwards made from the prepared plate); so that the artist will be enabled to judge of the effect of his work as he proceeds. When the engraving or etching has been performed, those parts of the subject which are required to be much deeper than the rest, as in cases of "broad lights," are "built up" with white wax, dissolved in spirits of turpentine, and applied with a brush. The surface of the composition is now rendered a conductor of electricity, and copper is deposited upon it, by the electrotype process, until a plate, or suitable printing surface, is formed.

Instead of producing the printing surface by electrotyping, a cast may be taken, in plaster of Paris, of the subject engraved or etched on the prepared plate; and in that case, it will not be necessary to build up the lights, as before directed, for the parts where they come may be readily cut away from the plaster cast; then, by rubbing the surface of the cast with a lather of soap, and taking a reverse cast, in plaster, a mould is produced, from which a printing surface may be obtained by casting in metal.

The second improvement consists in two methods of producing metallic surfaces, with designs thereon, to be printed from, in the ordinary manner of line or sunk engraving.

The first method consists in engraving or etching the subject or design upon a tablet, formed of two layers of composition, the upper layer being white and the lower one black; and hence, as every line pierces through the white surface into the dark ground, each mark will appear as if it were drawn with black color. When the drawing is completed upon the tablet, a reverse is taken from it, in metal, by the electrotype process, and from the reverse as many printing surfaces or copies are taken as may be required.

The white composition is made by mixing sulphate of lead and white wax together, by means of heat, and a thin layer of it is poured over a plate of metal; when cold, a border is formed around it, and a sufficient quantity of the black composition, (consisting of white wax, mixed with black lead, or other coloring matter,) in a melted state, is poured upon it. The tablet is thus formed, and is separated from the metal plate by pouring cold water upon the back of the latter.

The second method of producing these metallic surfaces is as follows:-A polished plate of metal or glass is slightly oiled, and a border made around it, and from this a cast is taken in plaster of Paris; by which means, the surface is rendered much more smooth and level than can be effected in any other way. After the cast has been dried, the outline is traced on it with a black-lead pencil, and the subject is engraved; the artist occasionally dusting a small