MORTAR, a preparation of lime and sand mixed up with water, which serves as a cement, and is used by masons and bricklayers in building of walls of stone and brick.
Mortar, when well made and of the best materiali, becomes as hard as stone, and adhering very strongly to the surfaces of the stones which it is employed to ce ment, the whole wall is as one single stone. To obtain this end the lime should be very pure. Earl Stanhope, who has made many experiments on this sub stance, found that almost every thing de pends upon the burning of the lime ; it must be almost vitrified to be completely free from the carbonic acid, and then re duced to a fine powder ; the sand should be free from clay, and partly in the state of fine sand, and partly in that of gravel ; the water should be pure, but if saturated with lime so much the better. The best proportions are said to be three parts of fine sand, four of the coarser kind, one part of quicklime, and as little water as may be. The stony consistence of mor tar is partly owing to the absorption of carbonic acid, and partly to the combina tion of part of the water with the lime ; hence, if to common and well made mor tar one-fourth part of unslacked lime, re duced to powder, be added, the mortar when dry acquires much greater solidity than it would otherwise. Morveau has given the following proportions.
Fine sand . . . . 30 Cement of well baked bricks . 30 Slacked lime . ,20 Unslacked lime . . 20 100 was= The best mortar for resisting water is made by mixing, with lime, puzzolano, a volcanic sand brought from Italy. Basal tes may be substituted in its stead.
MowraI, in chemistry and pharmacy, an utensil very useful for the division of bodies by percussion, trituration, &c. Mortars are of different shapes and sizes, and the matter intended to be broken in them is struck with a pestle made of wood, iron, or marble, according to the different degrees of hardness.
Moterxx piece, s short piece of ord nance considerably hick and wide ; serv ing to throw bombs, carcases, fire-pots, &c.
The use of mortars is thought to be older than that of cannon ; they being em ployed in the wars in Italy to throw stones and balls of red-hot iron, long before the invention of bombs; which, as Blondel informs us, were first thrown at the siege of Wachtendorch, in Guelderland, in 15E8.
It was formerly the opinion of gunners, that only one certain charge of powder, was requisite for each mortar, and that the honzontal range could not be altered but by changing the direction of the piece ; but, at present, when a place ly ing in the same horizontal plane with the mortar, is to be bombarded, they elevate the piece to 45°, and augment or dimi nish the charge of powder until they can hit the mark. The following advantages introduced this practice : 1. The public powder, is saved as much as possible ; be cause, at a direction of 45°, a less velo city, and consequently, a less charge of powder is required to make any horizon tal range, that is necessary to make the same horizontal range at any other eleva tion. 2. In elevating mortars to their
proper directions, gunners seldom come within a degree or two of the proposed elevation, both on account of the imper fection of the instruments which they ge nerally use for that purpose, and the hur ry they are in at that time. And in born barding towns from ships, it is scarce pos sible to come within two degrees of the designed elevation, because of the agita tion of the vessel, which continually changes the direction of the mortar. But by raising the mortar to 45°, the bad con sequences of this inaccuracy of elevation are in a great measure prevented, be cause a small error, above or below 45°, occasions a very ipconsiderrble error of amplitude.
For the same reason, also, places lying above or below the horizontal plane, pass ing through the piece, are bombarded by directing the mortar so as its axis may bisect the angle comprehended between a perpendicular to the horizon at the point of projection, and a line drawn from that point to the mark aimed at ; and then augmenting and diminishing the charge of powder until the object be hit.
When the business, therefore, can be effectually done by this middle elevation, it ought certainly to be preferred to any other. However, in the course of a siege it frequently happens, that several of the cases mentioned under the article Gus Naar are made use of, either by the as sailants or defendants. Whence we may infer, that though mortars are oftenest, and most fitly, used at 43° elevation, yet they ought not to be founded of one piece with their bed, because such are not only very costly, but unwieldy, and there fore unfit to be raised to any desired ele vation. See GUNNaaT.
Mortars are most fit for service, when hung by trunnions and propped with quoins, especially if their carriages be steady enough to prevent the effects of sudden recoiling.
In shooting with mortars, the following general rules should be always observed. 1. To measure the distance of the object aimed at. 2. That the bombs be of equal weight, otherwise the shots will vary. 3. That the carriage be on an exact level to prevent its leaping. 4. That the powder with which the piece is charged, be always of the same strength and quan tity. 5. That the charge be always equally rammed down. 6. That the wads be always of wood, tompions, or oakum. 7. That the fuses be fresh made the days on which they are to be used ; and that they be of a composition proportionable to the range of the shot in the air, so that the bomb may break at the very moment of; or soon after, its fall; which composi tion must be such as not to be extinguish ed though it fall in water, but continue burning till the bomb breaks. See Boma.