It appears that those dried in the sun were mixed with chopped straw. Dr Pocock describes one of the pyra mids constructed of brick : he measured some 134 inches long, 64 inches broad, and 4 inches thick ; also others, which were 15 inches long, 7 inches broad, and 44 inches thick. At Rome they were found by De Quincey of three different sizes ; the least were 74- inches square, and 11 inch thick ; the middle-sized were 16 inches square, and 18 to 20 lines in thickness ; and the largest were 22 inches square, and 21 to 22 lines in thickness.
Three kinds of sand are mentioned, that is, pit, river, and sea sand ; of these, pit sand was reckoned the best ; the white was preferred to the black or red-coloured, and the carbuncle to all ; of the river sand, that was con sidered best which was found near torrents ; the least value was put upon sea sand, and it was requii ed to be well washed, to dissolve the saline matter before used in plastering or rough casting walls.
Lime for plastering walls was made from shells, river pebbles, or a sort of pumice-stone ; the best sort of lime was accounted that made from white stone, which was dense and hard, and lost one-third of its weight in burn ing in a kiln, where it was kept about sixty hours. Their mortar was composed of one part lime and three of pit or two of river sand.
Metals were used, 1. Iron for chains, hinges, handles, and nails. 2. Lead for roofs pipes. 3. Copper and brass were still more used for many of these purposes; or, 4. Copper, brass, and lead, mixed into a bronze for statues, bases, and capitals of columns, and in doors.
Amongst the moderns, change of climate, natural pro ductions, and the habits of mankind, have from time to time led to considerable changes in the kinds of mate rials used for the various purposes of architecture, also in the modes of preparation, and application of them.
With regard to timber. Oak, for the greatest strength and durability, should be chosen from those soils where it has taken the longest time in arriving at maturity, and of two pieces equally dry, that should be chosen which has the greatest specific gravity, and that which will have its specific gravity least changed by being soaked in water : this observation will indeed apply to timber iu general. A decay of the top is almost a certain indica tion of a decay of the tree ; and a decayed branch or rut ten stump bespeaks a defect in that part of the tree where it is situated. In a similar soil, trees which grow near the outside of a forest will be more durable than those near the middle of it ; and in the same tree, the side which grew towards the north will be stronger than the south side.
When perfection of strength and texture is alone con sulted, all sorts of timber are cut down in the winter, be ing at that time freest of sap, and most readily seasoned, and rendered fit for the purposes of building ; but on account of the bark of the oak being of great use in tan ning leather, that wood is always, in England, cut in the spring, or rather from April to June, according to the state of the season, and soon after the sap begins to as cend and the leaf to appear ; if it is cut before the sap rises, the bark adheres to the wood, and cannot be strip ped off; and if left until the leaf is quite expanded, the bark is less ; when the tree is felled and suffer ed to lie in the trunk, it will shrink in size, but this is probably from its discharging water, because, if a dry tree be laid in a damp place, it will increase both in weight and size. The part called the sap varies in quan tity in different trees ; it is least in bad soils, where the growth is slow ; it is of very little use.
Oak, used in damp situations, appears to decay gra dually from the external surface to the centre of the tree ; the outside ring or addition it received in the last year of its growth decaying first, and afterwards that next within it, and then the following one. This appears to proceed from two causes ; first, from the outward ring being, where whole trees are used, first exposed to the action of the atmosphere, which cannot reach the second until the first is destroyed; secondly, from the centre part of the tree having arrived at a greater degree of maturity than the outward rings, which are many years younger. But this must be understood only of trees which are not past their prime before they are cut down ; for when a tree begins to decay from age, that part of the tree which is oldest, namely the central part, decays first ; to this succeeds the parts which are next oldest, being the ring next the centre, and the other annual rings in suc cession, gradually approaching the hark. A judicious builder will therefore, in the choice of his timber, al ways carefully examine the central part of the tree, es pecially of that which is next the root, and more particu larly if the tree is large, and has the appearance of great age.