Concave chambers. The advantage of these kinds of chambers consist in this, that their entrance may be made narrower than that of any other form; and practice has sufficiently proved it. Yet, when the entrance is so small as not to admit a man’s hand, they are not easily cleaned: for which reason it is supposed that all 13 and 10-inch mortars should have concave chambers, and the others cylindric ones.
Parabolic chambers. These chambers, being the widest of any, may therefore be included among the worst; as it is not the inward figure of the chamber, but its entrance, which produces the effect; because the smaller it is, the nearer it reduces the effect into the direction of the shell. It has however one advantage, namely that the shells will have no windage.
Mortar, in military architecture, a composition of lime, sand, &c. mixed up with water, that serves as a cement to bind the stones, &c. of any building. Mine sand makes weak mortar, and the rounder the sand, the stronger the mortar; and if the sand is washed before it is mixed, so much the better.
The proportion of lime and sand for making mortar is extremely variable. Some use three parts of pit-sand, and two of river-sand, to one of lime; others, a proportion of sand to quick-lime as 36 to 35. It should be well mixed, and beat every 24 hours for a week together, letting it then lie for a week more; and when it is used, must be beat and mixed again. By this means it will make good mortar, though the lime is but indifferent.
Mortar for water-courses, cisterns, &c. is made of lime and hog’s lard; sometimes mixed with the juice of figs, and sometimes with liquid pitch, which is first slaked with wine; and, after application, it is washed over with linseed oil.
Mortar furnaces, &c. is made with red clay wrought in water wherein horse dung and chimney-soot have been steeped; by which a salt is communicated to the water, that binds the clay, and makes it fit to endure the fire. The clay must not be too fat, lest it should be subject to chinks: nor too lean or sandy, lest it should not bind enough.
Mortar, made of terras, puzolana, tile-dust, or cinders, is mixed and prepared in the same manner as common mortar; only these ingredients are mixed with lime instead of sand in a due proportion, which is to be in equal quantities. As this mortar is to be used in aquatic buildings, the lime should be the very best.
In fortifications, docks, or piers of harbors, lay all the works under water with terras-mortar, and the rest of the facings, both within and without, with cinder or tile-dust mortar, for about two feet deep.
The East India Mortar for building and plaistering, is made with shell lime, brick dust pulverized, (called soorkee) washed sand, and the raw juice of the sugar cane, (called jaggeree.) The proportions of different kinds of work are different; but well made and mixed, surpasses all others; the roofs of houses, as well as the floors of their chambers, and the walls are covered with this composition, which, skilfully executed, bears a polish and smoothness like marble.
Mortes-Payes, Fr. Soldiers that were paid for the constant duty of a town or fortified place, both in the time of peace and war. Infantry regiments, which were occasionally stationed in citadels and garrisoned towns, took the right of the mortes-payes, and had the precedence in chusing lodgings.