Concerning the method of making fire-brick, Mr. Thomas Pickering, of Chicago, Ill., recently wrote to Mr. Davis, as fol lows : " Having made fire-brick in England for eighteen years in the county of Durham and in Northumberland, near New castle-on-Tyne, it may be of interest to you to give the methods of fire-brick making in those two counties. I will confine my remarks simply to the making.
"The clay is on the moulding bench, and on the bench is a piece of flannel about twelve inches square tacked on the bench to make the ball on. There is a piece of wood two inches thick, five inches wide and ten inches long, covered with flannel stretched as tight as possible.
"The stamp is nailed on with a staple driven in at the end of a piece of wood, so that when the mould is put on, the stamp will be right in the center of the brick.
" The mould is solid brass with a flange on the top side of the mould, with no bottom. The mould is about ten pounds weight, with one side of the mould a little lower than the other, to allow for a little sagging when the brick is put down on edge. The mould is put on the piece of wood covered with flannel.
" Then the ball is made and thrown into the moulds, the sur plus is taken off with the hand. Then a hardwood streaker is taken to smooth it off. The streak is then thrown into a little box filled with water in front of the moulder, which is called the streak-kit.
" The mould is emptied onto a pallet which is taken away by boys. Each moulder has two boys or girls. The moulder must be careful to have the short side of the mould to the left hand, so that when the boy takes the brick up to put it on the floor the short side will be on the bottom.
" Circle brick and cupola brick are made the same way, and tiles weighing as much as twenty-five pounds. The moulds for cupola and special brick are made of wood lined with plate zinc.
"Some places all the special brick weighing over twelve pounds are made by the ton, paying from elevenpence. to thirteenpence per ton. A moulder can earn from six to seven shillings per day, getting two shillings per thousand for brick. A moulder can make from 2,500 to 3,500 brick in a day." Drying and Tempering. The paste made, and the article completed, it must be dried or " tempered." This for cruci bles, retorts, etc., is commenced in the open air, and, if possi ble, out of the draft. If the draft cannot be excluded, the place where the drying takes place is slightly heated, commencing at a temperature from 6o° to 70° F., and keeping it up from
twenty-five to thirty days ; then increasing it from 8o° to I00°, leaving the article as long as possible, with an active ventila tion, but the same temperature being kept up. The article should remain in a temperature of from 150° to 18o° for at least six weeks. Brick, tile and blocks do not require so much care ; but crucibles and retorts do. Long experience has proved that there is a great economy in conducting this pro cess of tempering as slowly as possible, and that it influences materially the refractory nature of the article. It is found by actual experiment in crucible works that those crucibles made from the same mixture, tempered during six to eight months, last more than three times as long as those which had been tempered only two ; so that, in general, the older the article before being burned the better. This desiccation, while per haps it is the most important part of this manufacture, is un doubtedly the one most neglected. A poor article well tem pered is often better than the best which has been hastily dried. By working rapidly and filling up cracks as they form in a too-rapidly heated drying-house, with a very liquid material, in order to secure complete penetration, both time and money are lost. The material never lasts nearly so long as when slowly dried. In the works at Andenne, in Belgium, large pieces, like glass-house pots, are kept six months in the drying-house be fore they are used, and during this time the greatest care is taken to prevent drafts, so that no air colder than the drying room shall strike them. Leaving the door of the drying furnace open has been known to crack the pieces, which had been up to this point most carefully prepared and tempered.
The drying of fire-brick in the United States is done chiefly on fire-heated floors, but it is gratifying to note that floors heated by exhaust steam from the engine are at last coming to have their advantages recognized, as their construction and operation become better understood. These floors have been successfully used in England for many years. Both forms of dry-floors will be found fully described above. For large works there is no reason why the superior economy of tunnel-dryers should not be made available for drying the brick after being pressed.