twenty-nine inches, the outside being faced with bricks cut in squares; then brick and clay alternately, as high as the old ruins now remain standing. He adds some remarks on the hardness of the mortar, and durableness of the bricks, the length of which last is found to be 17,4-tenths inches, or a Roman foot and a half; their breadth 11,6-tenths inches, or precisely a Roman foot; and their thickness only 1,3-tenths of an inch. This last circumstance deserves particular notice, and we therefore refer the reader to the article Brick, p. 352.
Many compositions have, with more or less success, been devised for making mortar impenetrable to moisture. The following we believe is one of the most simple and effectual: Mix thoroughly one-fourth of fresh unslacked lime with three-fourths of sand; and let five labourers make mortar of these ingredients, by pouring on water, with trowels, to supply one mason, who must, when the materials are sufficiently mixed, apply it instantly as cement or plaster, and it will become hard as stone. This recipe is given by Mr. R. Dossie, in his second volume of "Memoirs of Agriculture and other Economical Arts," 1771. The author, on this occasion, observes that the lime used should be stone-lime; that previous to its use, it should be preserved from the access of air or wet, and the plaster screened for some time from the sun and wind. He justly remarks, that its excellence arises from the particular attraction between lime and sand, which would be destroyed by slacking the lime. Skimmed milk (says he) is preferable to water; and for the similarity of this mortar to that of the ancients, he refers us to Pliny, Vitruvius, &c.
Another very durable and cheap cement in building, which is particularly designed as a handsome coping of walls, is that of the late P. Wych, Esq. Take four or five bushels of such plaster as is commonly burnt for floors about Nottingham (or, according to Mr. Dossie, a similar quantity of any tarras, plaster, or calcined gypsum); beat it to fine powder, then sift and put it into a trough, and mix with it one bushel of pure coal ashes, well calcined. Pour on the water, till the whole becomes good mortar. Lay this in wooden frames of twelve feet in length on the walls, well smoothed with common mortar and dry, the thickness of two inches at each side, and three inches in the middle. When the frame is moved to proceed with the work, leave an interval of two inches for this coping to extend itself, so as to meet the last frame-work.
In December 1780, Dr. R. Williams obtained the King's patent for his invention of a mortar or stucco for the purpose of buildings. As the term of the exclusive privilege of using this composition is now expired, we shall give the following particulars: Take of sharp, rough, large-grained sand, sifted, washed, dried, and freed from all impurities; of well-burnt lime, slaked, and finely sifted; of curd, or cheese, produced from milk; (the first, fresh made and strongly pressed, to divest it of its whey; the second, whilst perfectly sound, rasped into powder with a grater, or brought into a very light substance with scrapers, or fine-toothed plane irons, in a turner's lathe); and lastly, of water in its natural
