Nevertheless, deposits of the latter do form in the brick lin ings of blast-furnaces, where the brick is not too hot. These formations must, however, not be ascribed to the presence of converted pyrites, but to particles of iron derived from the ferric hydrate obtained in the clay, or, also, to chips from the crusher in which the clay was ground. That the accumulations of car bon on these particles cannot increase to the extent of exerting a " breaking" strain on the brick in which they are lodged is almost self-evident, because the pressure which they exert within the brick cannot be greater than that of the air or gases inside the furnace, and also because the deposited carbon is of no greater density than the brick components are. Nor is there such a difference in the coefficients of expansion of im pregnated carbon and brick substance as to render it possible that the carbon should expand at an increased temperature sufficient to burst the brick, or that the brick should break at a lower temperature on account of the unequal contraction of the respective substances.
But what can happen very frequently is, fire-brick bursting on account of the sudden expansion of its free silica at high heat. Cracks may then open in the brick wide enough to let even carbon lumps of hazel nut size drop into them from the descending burden ; and when, at a receding temperature, these cracks become partly closed, then the carbon lumps that have dropped in will be held so tightly as to give rise to the suppo sition that the brick had been ruptured by their expansion. This belief is apt to be strengthened when other (but smaller) aggregations of carbon are found to obtain in unfractured parts of the same brick, into which they could not have dropped from without.
The conditions for the complete desulpurization of contained pyrites obtain sometimes in the fire-brick kiln, but not in the blast-furnace lining ; and the blast-furnace briCk may contain impregnated carbon that has been formed within, as well as carbon that has dropped in, but neither is likely to cause the rupture of the brick.
Fire-Brick. Special Shapes.—A large proportion of the work done by the leading fire-brick manufacturers is on special orders for all kinds of irregular and difficult work. To endeavor to fully illustrate this department of fire-brick manufacture would be impracticable as well as useless. In order, however, that the reader may have a good idea of the leading specialties in the different departments, ordinarily kept in stock, we have drawn on the catalogue of the well known firm of Harbison & Walker Co., of Pittsburgh, Pa., for the illustrations shown in Figs. 102 to 125. It is of great importance in ordering refrac tory materials of any character to state explicitly the nature of the service required of the ware, when the orders are given, so that the manufacturer can fill them with the stock best suited for the purpose.
Sorting Fire-Brick—There are three grades of fire-brick which can be recognized. The first or No. 1 is the best and most refractory, and is intended for the severest use, such as the hearth and boshes of the blast-furnace, the exposed parts of puddling-furnaces and steel-mill plants. Its application en forces the use of a very large proportion of calcined and flint clays with the least possible plastic clay which will bind them together. In several places the mixture is composed of about half and half of each of these, with no plastic, and the mixture is ground very severely in a heavy wet-mill for a long time.
The more usual charge for a No. I brick consists of about 45 per cent. of both flint and calcine and to per cent. plastic.
The cohesion among the particles of such a mixture is very slight, and very light friction suffices to shell the brick up into its component parts; it is of course unfitted for use in any position where friction will be brought to bear, but at the in tense heat at which they are used, the softening of the clay makes them as cohesive as need be, and in that state the fric tion of matter as highly heated as the brick has but little effect.
The next well-marked grade of brick has neither name nor number among its makers. It is composed of about equal amounts of both flint and calcine, and about three times as much plastic as the No. t brick.
Its proper uses are the same general kind as those for the No. t brick, but the product is a little inferior to it. The next grade, or No. 2 brick, is made of about so per cent. of plastic, 20 per cent. calcine and 3o per cent. flinty clay; it has a homogeneous appearance on its fracture, is close-grained, and emits a sharp ring when struck with another brick. Such a brick will sometimes stand a very fair heat with no symptoms of fusing, but as a rule it is not fitted for any responsible posi tion. It is excellent material from which to make kilns, etc., except the hottest parts. What might be denominated a No. 3 brick consists of a mixture of several plastic clays, or else a body made of one plastic grade. They are generally vitrified slightly in the burning heat of a kiln, and precaution must be taken to keep them from sticking together. They are excellent for making flues, pavements, boiler-settings, chimneys, etc., and as they can be well made by a machine they ought to be fur nished at low rates. The burning of these various grades of brick demands considerable technical skill. The products ex hibit many phenomena which are very interesting; iron, in particular, is noticed in the black blotches which its union with silica has caused.
Often a nail, bolt, or some stray piece of iron gets into a kiln of brick. Its effects can be seen in a large conical hole in the brick, lined with the black cinder of iron, and extending down ward as far as the iron lasted. The blackening of the faces of the arch brick and those most exposed to the direct heat of the fires has often been mentioned by brick men as being the re sult of impure fuel and sulphur in the coal. This explanation is incorrect ; sulphur, i. e., sulphide of iron, when burned in a grate would decompose to SO, or sulphurous anhydride, and in that state would pass into the kiln. The only effect the gas could possibly have on hot silicate of alumina or anybody likely to be present in clay, would be to recombine in the same state from which it has just been expelled by a less heat than is met in the inside of a kiln. The true explanation is this: the heat on the brick that are blackened is more intense than on any other part of the kiln, and they are rendered softer and nearer to fusion ; while in this pliable state the draft from the fires just outside carries in a very appreciable amount of dust and ashes, which lodge on these portions and flux outside to the black crust seen.
Blocks, Tiles and Special Pieces, and their Illanufacture.—In addition to the manufacture of fire-brick the same establish ment usually produces many other kinds of wares, notably, blast-furnace linings and special pieces.