We conceive that the mixture of about one-fourth of chalk with the clay of which the London bricks are made, would greatly improve their quality. The consequence would be an incipient fusion, which would render their surface much more compact and solid. The only difficulty would be to proportion the quantity of chalk so as to prevent complete ra• aion, which would run the bricks into each other, and destroy them entirely. Bricks made of mate rials which have undergone complete fusion, would be greatly superior to common bricks. They would resist the action of the weather, and would, therefore, last much longer than common bricks. 'In Sweden it is customary at some of. the iron foun deries, to cast the aconite into bricks, which they employ in constructing their furnaces. Such fur naces the writer of this article has seen; and he was assured by the gentleman who had the charge of the works, that they answered fully better than common bricks. It would be easy to make any quantity of such bricks in some of the large iron founderies of Great Britain. We are persuaded that such bricks might be brought into use for a variety of purposes with great advantage, and might even constitute a lucrative article of manufacture. Bricks made from scoriae of iron and copper founderies, would vie in beauty with marble and porphyry, and would pos • sess a smoothness of surface and a lustre to which few marbles could reach.
Few parts of Great Britain are so well adapted for the making of bricks, according to the London plan, as the neighbourhood of Newcastle upon Tyne. There the enormous heaps of small coal, which are of no use whatever, would furnish abundance of fuel, at a much cheaper rate, than even the London ashes; while the magnesian limestone that occurs in such plenty in the neighbourhood of Sunderland, would enable the brickrnaker to give the clay the requisite degree of fusibility.
As bricks form an article of taxittion, and furnish a'considerable revenue to Government, their size has been regulated by act of Parliament. They must not be less than 81 inches long, 24- thick, and inches witie. But for various purposes, they are made a very different and very considerable sizes.
Fire-brisks are made in the same way as commOn bricks. But the materials are different. The best clay for their composition is Stourbridge clay ;'and, instead of sand, it is usual to mix the clay with quantity of old fire-bricks, or crucibles, or glass pots, reduced previously -to powder. This mixture an swers the same purposes as sand, while it does not communicate the tendency to fusion, when it comes in contact with various fluxes, that is communicated by siliceous sand.
Motor. lth. xxxv. c. T4.) Pliny does not mention the part of the world 'in which 'the earth employed in the manufactures elf these bricks was found; though in all probability, •it could not be for from the cities where the bricks are said by Pliny to have been made. He says %that material employed was a kind of pumice stone. But it qmte un known to the moderns, till, in the year 1791, Fab broni found a substance at Castel del Piano, not far from Santa Fiore, situated between Tuscany and the Papal dominions, which formed bricks capable of Swimming in water. This is a white earthy matter, which constitutes a 'bed in that place, and known in Italy by the name of Latta di Luna. In more recent mineralogical books, it is distinguish ed by the name offarinafossilis (bergmehl). Hauy considers' it as a variety of talc, and Brochant, as a variety of meerschaum. According to the ana lysis of Fabbroni, this substance-is -composed of We seeTrom that this mineral is neither a variety of talc nor of meerschaum. One would be disposed to consider it as a hydrate of silica. For both the alumina and -oxide of iron are present in so small .proportions, that we can scarcely consider them as in chemical combination.
Considering the composition of this earth, it is rather singular that his capable of being agglutinat ed by a red heat. We rather suspect that the bricks of Fabbroni, -which swim in water, have but very little strength. This, if it be the case, must greatly circumscribe their utility.
The colour of the London bricks is not red, as is the case with common bricks and tyles ; but a light brownish yellow. This colour is more pleasing to the eye than common brick red, and on that account the London bricks are -preferred for building houses. The brickmakers assign a curious enough reason for this colour. According to them, their bricks are kept as much as possible from the contact of air dur ing their burning. .The consequence of this is, that the iron contained in them is not oxidized to se great a degree as in common bricks. But this mode of reasoning is far from exact. If air were excluded entirely, the bricks would not be burnt at -all, be cause the fire would be extinguished., But if enough of air be admitted to burn the coal mixed with the clay (which must be the case), that air must also act upon the iron, and reduce it to the state of peroxide. Indeed, there can be no doubt, that the iron in the London yellow bricks, is in the state of peroxide, as well as in the red bricks ; for the peroxide of iron gives various colours to bodies, according to circum stances. We find bodies tinged with it, red, yellow, B R I which, byunit with the peroxides of hob, !bliss a kind of yellow Mire.
B R sad brown, wording so the giaisiateei *4th which the oxide is combined. We meribe the yellow lour of the London brisk, to whew of the coakr, •