Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 1, 1802).djvu/380

348&#93; 348] BR I in a cheat? and expeditions man- ner. Such appears to be the ten- dency of the patents that have, from tim, j. to time, been procured by va- rious scheming men, who are gene- rally ignorant of the first principles of chemistry, on which the' success- ful practice of this important branch of the arts chiefly depends. In order to afford a concise view of the subjeKft, we shall premise an analysis of the r quisites of a pro- per claij for making bricks ; then Mate a f/w rules applicable to prac- tice in all situations ; and conclude with a general account of the late invent ons, for which the King's pa- tent has been granted: by which means the reader will be enabled to ascertain their respective merit. It is an erroneous notion, that bricks may be made of any earth that is not stony, or even of sea- ouse ; for those only will burn red, which contain iron particles. In England, they are chief!}' made of a motley, yellowish, or somewhat reddish, fat earth, vulgarly called loam. Those of Stourbridge clay, and Windsor-loam, are esteemed the most proper and durable bricks ; such as will stand thegreatestdegn e of heat, without melting. In gene- ral, the earth for this manufacture Ought to be sufficiently fine, free from pebbles, and not too sandy ; which would render the bricks • " and brittle; nor too fat, which would make them crack in drying. Nor should it contain too many calcareous and ferruginous ingr; di< .its ; as the former prevent the mass from becoming firm in burning, and occasion the bricks to - rumble, when exposed to the air 5 while the latter, or iron particles, retard the preparation of bricks, in- somuch that it is sometimes impos- sible to <rive them due consistence : BRI this inconvenience, however, may be remedied, by allowing the clay to lie for a considerable time under the. influence of the atmosphere, then soaking it in pits, and after- wards working it well, in tire usual manner. — The common potter's clay, which is also employed for the manufacture of bricks, is opaque, imparts a slight colour, sometimes yellowish, blueish, greenhh, but more frequently of different shades of light-grey, excepting that of blue, which is always dark : by kneading" and spreading such clay, it becomes smooth and glossy ; it is soft, fat, and cold, though agree- able to the touch, slightly adheres to the tongue, and, when of the best quality, it should neither be too light nor too heavy. Its con- stituents chemically examined, are found to consist of thirty-seven parts of pure argillaceous or clayey earth, and sixty-three ; parts of afli^ cious or flinty earth. Whoever is desirous of produc- ing the best and most durable kind of bricks, ought to attend to tire following rules : 1. Clay of every description, whether fat or lean, whether more or less mixed with particles of lime, iron, &cc. must be dug after Midsummer, that is, between the beginning of July and latter end of October, before the first frost appears : it should be re- peatedly worked with the spade, during the winter, and not formed into bricks till the following spring. 2 . The clay, before it is put into pits for soaking, must be broken as small as possible, and allowed to lie at least ten days : every stratum of twelve inches should be covered widi water, as in this manner it will be more uniformly softened. 3. Two such pits, at least, will be necessary for every brick-manu- facory 3