With reference to the proportion which should be observed in mixing the ditferent ingredients, it is impossible to lay down any fixed rules, as such proportion must entirely depend upon the particular quality of the materials employed. The principal of these consist of clay, marl, and loam, with the admixture of sand, chalk, breeze, &c. We shall here give the particular uses to which the accessories are applied, but must leave it entirely to individual instances to determine in what manner each of them must be made use of. The clay of course is the principal matter, and forms the body of the brick, but befi we this can be made available for building, it has to be agglutinated together by means of sand vitrified by heat. Clay is composed for the most part of alumina and silica combined with a small quantity of' lime, and occa sionally of magnesia and alkali. Usually speaking, clay requires additional sand to be used as a flux, but it happens sometimes to contain sufficient in itself; when this is the case, no addition of course will be required. It' the silica be in excess, it will on the contrary require the addition of some dry substance to hold the mass together, as otherwise the silica will fuse and run when under the action of great heat ; for this purpose the chalk is used : if, however, too much be added, the bricks will become porous and friable.
The heat, as above stated, is produced by means of the breeze, but the quantity of this also must be regulated according to the nature of the clay you have to use ; if it contains a large quantity of sand, less breeze will be required, not only to prevent the silica from running, but also because silica con tams a large portion of oxygen : should, however, the elav contain a free proportion of lime, more breeze will be required, for the reason that lime has but little oxygen in its comp°. sition. Thus it will be seen how impracticable it is to lay down any general rule in this case ; the proportion of each ingredient to be added, can only be determined by careful observations in individual instances.
Every stony particle should be carefully cleared out of the earth, before the workman begins his operation of tempering: it should then be well trodden or beat, and frequently turned over, with the addition of as little water as possible, till the soil and ashes, or sand, are so completely incorporated as to form a paste of a tough viscous substance. It' in this operation too much water be used, the paste will become almost as dry and brittle as the soil of which it is composed ; but by a judicious management, as to the quantity of water, and the mode of administering it, the bricks become smooth, solid, and durable.
For the preparation or tempering of the soil, the workman is provided with a long hoe, in form like a mattock, a shovel, and a scoop. The hoe is for pulling down the soil from the
great heap, which is then chopped backwards with the shovel, in order to turn it as often as may be necessary, and to incorporate the ashes, or sand, and soil, thoroughly together. The use of the scoop is for throwing water over the portion so pulled down with the hoe, to bring it to a more ductile state, and render it easier for tempering. When the mass is sufficiently mixed, it is removed in harrows to the pugmill. This consists principally of a strong barrel, firmly fixed on two transverse beams, having in its centre a vertical bar, kept in position by two shoulders attached to the sides of the barrel, and working on the transverse beams at their inter section as on a pivot. On the top of this bar is placed a horizontal beam, by means of perpendiculars suspended from which, the horse is attached. On that part of the bar which is within the barrel, is fixed several iron knives, by the revolution of which the masticated clay is forced through a hole in the bottom of the barrel, when it is cut off in pieces with a " cuck-hold," or concave shovel, and laid on one side. A quantity of sand is then thrown over it, and it is kept tb• use under a covering of sacking or matting, to preserve it from the sun and air.
The moulding-table is placed under a movable shed, and is strewed with dry sand. A boy, with the cuck-hold, cuts off as much as he can carry in Ids arms, from the prepared mass, and brings it to the table, \ here a girl receives it, and rolls out a lump rather larger than the mould w ill contain. The moulder receives this lump from the girl, throws it into his mould, previously dipped in dry sand, and with a flat smooth stick, about eight inches long, kept for the purpose in a pan of water, strikes off the overplus of the soil : he then turns the brick out of the mould upon a thin board, rather larger than the brick, upon which it is removed by a boy, and placed on a light barrow, having a lattice-work frame raised about three feet above the wheel, and about eighteen inches at the handles, i;•riling an inclined plane. On this lattice-frame the new-made bricks are laid, and sand is thrown over them, to prevent their sticking to each other, as well as to preserve them in a certain degree from cracking in drying on the hacks. The hacks for drying, are each wide enough for two bricks to be placed edgeways across. with a passage between the heads, for the admission of air, to facilitate the circulation of which, the bricks are generally laid in a diagonal direction. The hacks are usually carried eight bricks high; the bottom bricks at the ends are com monly old ones.