CHAP. 51.—THE VARIOUS METHODS OF BUILDING.
The Greeks construct party-walls, resembling those of brickwork, of hard stone or of silex, squared. This kind of stonework is what they call “isodomon,”[2789] it being ” pseudisodomon”[2790] when the wall is built of materials of unequal dimensions. A third kind of stonework is called “emplecton,”[2791] the two exteriors only being made with regularity, the rest of the material being thrown in at random. It is necessary that the stones should lie over one another alternately, in such a way that the middle of one stone meets the point of junction of the two below it; and this, too, in the middle of the wall, if possible; but if not, at all events, at the sides. When the middle of the wall is filled up with broken stones, the work is known as “diatoichon.”[2792]
The reticulated[2793] kind of building, which is mostly in use at Rome, is very liable to crack.[2794] All building should be done by line and rule, and ought to be strictly on the perpendicular.
CHAP. 52. (23.)—CISTERNS.
Cisterns should be made of five parts of pure, gravelly, sand, two of the very strongest quicklime, and fragments of silex not exceeding a pound each in weight; when thus incorporated, the bottom and sides should be well beaten with iron rammers. The best plan, too, is to have the cisterns double; so that all superfluities may settle in the inner cistern, and the water filter through, as pure as possible, into the outer one.
CHAP. 53.—QUICK-LIME.
Cato[2795] the Censor disapproves of lime prepared from stones of various colours: that made of white stone is the best. Lime prepared from hard stone is the best for building purposes, and that from porous stone for coats of plaster. For both these purposes, lime made from silex is equally rejected. Stone that has been extracted from quarries furnishes a better lime than that collected from the beds of rivers; but the best of all is the lime that is obtained from the molar-stone,[2796] that being of a more unctuous nature than the others. It is something truly marvellous, that quick-lime, after the stone has been subjected to fire, should ignite on the application of water!
CHAP. 54.—THE VARIOUS KINDS OF SAND. THE COMBINATIONS OF SAND WITH LIME.
There are three kinds of sand: fossil[2797] sand, to which one-fourth part of lime should be added;[2798] river sand; and sea sand; to both of which last, one third of lime should be added. If, too, one third of the mortar is composed of bruised earthenware, it will be all the better. Fossil sand is found in the districts that lie between the Apennines and the Padus, but not in the parts beyond sea.