COMPOSITION OF D1NAS " CLAY." Silica 98.31 .96.73 Alumina 0.72 Protoxide of iron 0.18 0.48 Lime 0.22 0.19 Potash and soda 0.14 0.20 Water combined 0.35 0.50 99.49 These analyses were made by Prof. W. Weston. No. I was rock of medium hardness, which was obtained near Point Neath Vaughan, and No. II was from the same locality, though not from the same mine. The powder of the rock is mixed and ground in a 9 foot wet-pan with about I 12 per cent, of lime, and sufficient water to make it cohere slightly by pressure. A sober man should be employed to see that the ingredients used in giving the brick the bond are very evenly distributed in the pan, as this is one of the most important things to do in order to have the brick uniform in size. Good men should be employed at the pan, men who will see that every pan of the material is ground alike, as in no case should one pan be ground fine and the next pan ground coarse. Every pan of material should be ground alike, or the brick cannot be made uniform in size, as the expansion will be greater in some brick than others. The mixture of ground quartz and lime is pressed into iron moulds, of which two are fixed under one press, side by side. The mould, which is smaller than the brick is to be, is open at the top and bottom, like ordinary brick moulds, is closed below by a movable iron plate, and above by another plate of iron, which fits in like a piston, and is connected with a lever. The machine being adjusted, the coarse mixture is put into the moulds by a workman, whose hands are protected by stout gloves, as the sharp edges of the fragments would otherwise wound them. The moulds having been perfectly filled, the piston is then pressed down, after which the bottom plate of iron on which the brick is formed is lowered and taken away with the brick upon it, as it is not sufficiently solid to admit of being carried in the usual man ner. The brick are dried on these plates upon hot floors warmed by flues passing underneath ; and then they are pressed in hand presses and put on a floor made twice as hot as the floor they are moulded on, so they will dry very quickly. The Savage Fire Brick Co., Hyndman, Pa., uses with most satisfactory results several Raymond Power Represses made by C. W. Raymond & Co., Dayton, Ohio, for pressing silica fire brick. When dry they are piled on end, usually in circular down-draft kilns, similar to kilns in which ordinary fire-brick are burned. The brick must be set in one kiln properly. Every head or bench should be perfectly level, so that the brick can settle evenly, and the setter should be very careful to allow enough room for expansion. About 8 days' hard firing are re quired for these brick, and about the same time for the cooling of the kiln. The cooling can not be hastened without detri ment to the brick. One kiln containing 50,000 brick consumes 65 tons of coal, half free-burning, and half binding. The heat required to burn a silica brick is so high as to burn a second grade fire-brick to a running mass. In the burning of silica brick the heat has to be equal to the highest grade of fire-brick and has to be held fully twenty-four hours longer than for the highest grade of fire-brick made from the non-plastic or flint fire-clays. Silica brick are manufactured of various shapes and sizes, to suit the furnace builder.
The fractured surface of these brick is uneven, showing coarse irregular white particles of quartz, surrounded by a small quantity of light-brownish yellow matter. The lime
which is added exerts a fluxing action on the surface of the fragments of quartz, and so causes them to stick together.
• From their silicious nature it is obvious that silica brick should not be exposed to the action of slags rich in metallic oxides.
So scrupulous are the managers of some works producing silica brick that they cause the silica to be weighed after com ing from the Blake crusher and before being put in the wet pan ; the same care being exercised in determining the quantity of lime admitted into the wet-pan with the charge of silica to be ground. Other manufacturers of silica brick do not weigh the constituent materials, but judge the proper mixture by the consistency of the lime liquid and by the stiffness of the ground mass. The silica material is ground and mixed in all respects the same as for ordinary fire-brick. The greatest watchfulness is required to be observed in the preparation of the lime liquid which forms the bond or binding material which unites the silica. The quantity of lime contained in the mixture must not be excessive—it should not exceed two per cent. of the entire body in the best grade of silica brick. The knowledge of the manner in which the binding material is prepared so as to ob tain the best possible results from the smallest quantity of lime is one of the principal points where the practical experience of men trained in the business of silica brick manufacture is of great value.
The lime used as a binding material in the manufacture of silica brick is dissolved in a board box similar to that used by plasterers, and from this box the lime is run in a thin state into the settling vat. From this settling vat the lime is gently de canted into the third vat or barrel, care being observed that none of the thick sediment from the lime is taken up from the bottom of the settling vat. It is necessary that the lime should be as nearly pure as it is possible to get it, as also the carbon ate of lime which is in part used. In the third vat or barrel there is placed a spiral agitator which lifts the material always from the bottom of the vat or barrel, thereby keeping the lime of a uniform consistency and preventing the heavier particles of lime from settling to the bottom of the vat or barrel from which the lime solution is run by means of a small pipe into the wet-pan, to be there incorporated with the silica which is being prepared for the moulders.
There are several firms in the United States at present engaged in the manufacture of silica brick, among which are Harbison & Walker Co., Pittsburgh, Pa.; The Savage Fire Brick Co., Hyndman, Pa. ; Reese, Hammond & Co., Bolivar, Pa.; A. J. Haws & Son, Johnstown, Pa. A large part of the quartz used by the manufacturers of silica brick in the State of Pennsylvania is quarried in Wills Mountain, Pa.
Great care should be used the silica quartz ; and in order to do so, good reliable men should be employed in the quarry, men who are acquainted with the quartz, as this is most important.
The silica brick now made in the United States by the lead ing manufacturers will equal in quality the imported Dinas material.
The following is the result of an analysis of one of the " Star Silica " brick : Gentlemen:—The report below gives the analysis made at our Homestead Works, of Silica Brick of your manufacture: