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tioned, and partially through the laths; and in these another series of laths or tongue-pieces are inserted; then into the spaces between the laths, any suitable cement is run, and when it is cold, the block is removed from the frame.

Another mode of forming or combining blocks, is by the use of cast-iron plates, as shewn in Plate V., fig. 1. a, is a plate, having dove-tail ribs or feathers b, upon their upper surfaces, into the spaces between which, the blocks or pieces c, are driven, the lower edges of the blocks being grooved, in order to correspond with the shape of the ribs b.

The second improvement consists in combining small pieces of thin planks, in the manner shewn in fig. 2, so as to form surfaces of great extent and strength, applicable to flooring and roofing houses, &c.

The pieces are arranged in layers, one above another, until a surface of the intended size and thickness is produced, care being taken, that the pieces in each layer shall overlap the joints, as respects each other, and the pieces in one layer shall overlap the joints in the pieces in the other layers,-thus producing a bond, as in brick-laying. The layers are now fastened together by pegs, nails, or screws, and may also be further secured, at the joints, by a coat of any suitable glutinous substance; or, instead of this mode of fastening, each layer may be glued to the next.

The third improvement consists in a method of covering cast-iron rails for railways;-this is intended to protect them, in a great measure, from the shocks and consequent risk of fracture, to which they are exposed when the wheels of the carriages run in immediate contact with them.

A rail, or rather framing, is made of the form shewn at d, in the section, fig. 3, and receives a rail of hard wood e, upon which the wheels of the carriages travel.

The patentee claims, Firstly.-The method of forming blocks, for covering surfaces, by means of small pieces of wood, joined together by means of keys or feathers, crossing each other on the under side, or by means of an iron plate, with dove-tail ribs.

Secondly. The method of forming a species of con

tinuous covering for surfaces, of almost any extent, by the "super-position" of layers of small pieces of thin planks, in the manner described.

Thirdly. The covering of cast-iron rails, in the manner described. [Inrolled in the Inrolment Office, July, 1842.]

TO MILES BERRY, of 66, Chancery-lane, in the county of Middlesex, patent agent, for certain improvements in the manufacture of prussiate of potash, and prussiate of soda, being a communication.-[Sealed 21st January, 1840.]

THIS invention consists in a more economical method of manufacturing prussiate of potash and prussiate of soda, than has been usually employed. Hitherto, prussiate of potash has only been obtained by incurring the loss of a considerable quantity of azote or nitrogen gas, which, when combined with carbon, forms cyanogen, the generator of prussian blue. This azote is evolved by the distillation of organic substances, contained in certain vegetables, animal oils, &c., but it is obtained in large quantities by the calcination of animal substances, such as horn, blood, muscular flesh, skin, &c. Sometimes the azote is evolved under the form of sub-carbonate of ammonia and nitrogenous oils.

To avoid the loss generally incurred, which is of serious consequence in the manufacturing of prussiate, it is necessary to treat the primary matters in a different manner, so as to collect the azote which escapes during the distillation, and to make it enter into combination with carbon, iron, and potassium; and, moreover, to convert to useful purposes; the azote which has adhered to the carbonaceous residuum. This end is obtained as follows:

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Instead of collecting the sub-carbonate of ammonia, in or by an absorbent medium, it is made to pass through a quantity of charcoal, iron, and potash, placed in an iron tube, kept at a red heat. The carbon, on the one part, decomposes the sub-carbonate of ammonia, and creates bi

carburetted hydrogen, and at the same time gives up part of it to the azote, which proceeds from the decomposed ammonia, and thereby forms cyanogen, which, in its turn, combining with the reduced potash, forms cyanoferruret of potassium or prussiate of potash. To obtain the most complete reaction, the operator must divide or reduce the ingredients constituting the decomposing compound. In order to effect such a division, either of the following means may be used, according to circumstances.

First method.-Reduce the charcoal into fragments of about the size of a nut or walnut; then dissolve the potash or salts of potash, such as carbonate or nitrate, in an aqueous solvent; in urine, for example, if a great quantity can be obtained easily, and at little cost; otherwise, use common water. With respect to iron, it is to be rendered soluble by the addition of an acid, such as nitric or acetic acid. These preliminary preparations being made, which are simple, the solution of potash and nitre is then to be poured on the charcoal; (the saline lye is absorbed very soon;) then pour in the solution of iron, stir the mixture with a spatula, evaporate the water which has been used as a dissolvent, taking care that the compound does not become calcined during the operation. The compound being dry, is again pulverised and introduced into cast-iron tubes, as will be hereafter mentioned.

The other method, is the substitution of a mechanical division, instead of an atomical or chemical one. To effect this, introduce the potash, nitre, and charcoal, into a barrel with iron filings,-place in the barrel cannon balls; then cause the barrel to revolve on its axis, and the balls will grind the compound, and reduce it to small fragments, which will thereby be mixed together. The compound is then removed from the barrel, and introduced at once into cast-iron pipes, or kept for use in a dry place.

It is not of importance to name any particular proportion in the ingredients employed, as they may be varied according to the will of the operator; but the following proportions have been found to give satisfactory results.

When the dry process is employed with the mechanical

division, take of ordinary potash 20 parts; saltpetre 10 ditto; iron filings 20 ditto; coke or ordinary charcoal 45 to 55 ditto; dried blood 50 ditto; and proceed as above stated. For the wet process or the chemical division, take of ordinary potash 30 parts; saltpetre 10 ditto; acetate or nitrate of iron 15 ditto; coke or ordinary charcoal 45 to 55 ditto; dried blood 50 ditto; and proceed as described.

Whether the wet or dry process be preferred for obtaining or effecting the mixture, the compound ingredients must be introduced, when perfectly dry, in a series of pipes, connected together, and contained in a furnace, similar to that used for the manufacturing of carbonated hydrogen gas or coal gas, employed for illumination. Instead of placing the pipes in a horizontal position, which renders it somewhat difficult to introduce and draw out, or remove the charge, they may be placed vertically; but then the heating is more expensive. If the pipes are placed vertically, care must be taken not to pulverize completely the dry compound, in order that the gases may be able to circulate through them without raising the internal pressure to a dangerous pitch.

The animal matter is placed in a separate compartment and in a cast-iron retort, which is connected with the horizontal or vertical pipes. On this retort is placed a safety valve, to prevent accidents, which might arise from any obstacle obstructing the circulation of the gases through the pipes. The heating of the furnace should be effected as follows:

It is very essential to bring to a red heat the pipes containing the compound or mixture, before any fire is placed or introduced under the retort, in order that, from the beginning of the operation, the decomposition of the gases may take place. The gas, which is evolved by the decomposition, is inflammable when issuing from the pipes, and the color of the flame will be a sufficient indication of the process of the operation. The color generally differs but little from that of the heated cast-iron pipes in the furnace. When this color approaches to pink, the reaction is almost complete, so that very little, if any, am

monia has escaped decomposition. When the jet of gas becomes smaller and clearer, while a good fire exists under the retort, the operation is near its end; the animal matter is reduced into azotated or nitrogenated charcoal, which is used, at present, for the manufacturing of prussiate of potash, and which is still to be employed in the same manner, and treated as usual. On the other hand, the azote, ammonia and other gases, by combining with the decomposing substances contained in the pipes, have been transformed into prussiate of potash. The charge must then be directly removed from the pipes, and being at a red heat, it should be thrown at once into water to extinguish it rapidly. The whole must be well stirred and allowed to settle. The clear liquor is then to be drawn off, and this is the strongest solution; warm water is then to be poured on the carbonaceous residuum, and being well stirred, and afterwards allowed to settle, the liquid is drawn off. This operation is continued until the residuum is exhausted. The strong solutions are to be evaporated and allowed to crystallize; the prussiate is then extracted according to the old process. The solutions which will not crystallize, contain carbonated potash; this is extracted therefrom, to be employed again. The same is done with reference to the residuum of charcoal and iron. All this residuum is carried to the following operation, to which is added the animal charcoal, furnished by the first operation, by the calcination of animal matter. Besides this animal charcoal, a proper quantity of fresh charcoal is added, in order to preserve, as far as possible, the same proportions in the decomposing mixture.

After some operations, it may be found, that the animal charcoal is completely deprived of azote; a portion of it is, in such a case, to be laid aside, and a proper quantity of fresh animal charcoal to be substituted..

It will thus be seen, that after a little while, the coke or vegetable charcoal, first employed, is completely set aside, and the whole operation is effected by two kinds of animal charcoal, of which one is almost deprived of azote, and the other contains a great quantity of the same.

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