Page:Architectural Review and American Builders' Journal, Volume 1, 1869.djvu/642

 518 The Architectural Review and American Builders' Journal. [Feb., lime, with a ring, or embankment of sand, placed on the surface of the ground, of sufficient capacity to contain twelve or fifteen bushels of lime. The tender then floods this lime with water, and when it is slaked, he covers it with sand, mixing it with his hoe, to make up the mortar. In general, but two or three parts of sand to one of lime are used, thus making a very rich, but a very weak mortar, which will crack, when dry, and require a long time to harden. In general, too, our masons prefer mortar which has been made for a long time : some even contending, that a bed of mortar which has lain all winter, is better for build- ing, than one recently made. But, when we know, that, as soon as the ingredients of the mortar-bed are brought into contact, a chemical re- action takes place between them, and that new chemical combinations are formed, we must be satisfied, that after these combinations have been formed in an old mortar-bed, the remixing, or breaking up of the bed, is mechanical, and we have little else than a mechani- cal mixture. It is true, that these chem- ical reactions take a long time for com- pletion, ancHfhat, even after the disturb- ance and recomminution of the mortar, the}' may continue, quite to the harden- ing of the mortar, when spread out in the wall, and in contact with the atmo- sphere ; but, it is equally true, that the mortar will not be as strong, or as hard, as if it had been used when first made. The most ignorant man must, when he reflects, satisfy himself, that the hard- ening of mortar being due to chemical combinations, this hardening should take place in the wall, among the stones : the strength of a wall, built of rough stones, of irregular form, is doubtless, to a great extent, dependent upon the strength and hardness of the mortar, and this must be greater, when uninterrupted by mechanical means, than when broken up, after remaining in the mortar- bed for months, or daj r s, or even hours. The very moment the constituents of the mortar-bed, the lime, the water, and the sand, are brought into contact, by the manipulations of the tender, or mortar- maker, that moment chemical reaction between some «f these constituents com- mences. It is generally conceded, be- sides this, that freshty-made mortar penetrates the stones of the wall, form- ing there combinations, which bind the stones of the wall together, so that, after a time, the structure becomes mechani- cally homogeneous, and is firmly ce- mented together. What earthly object, then, can there be for delay, in using the mortar when first made, or for making more at a time, than can be used with- out dela}^ ? Lime has a powerful affinity, or per- haps, more correctly speaking, a ready affinity for carbonic acid. This may be seen, b} r exposing a clear solution of lime, in water, to the action of the at- mosphere. In a short time a white pel- licle will form, on the surface of the so- lution, which is carbonate of lime : this will settle, in the form of a white solid matter, to the bottom of the vessel con- taining the solution, thus illustrating, in part, the action which takes place in mortar. The carbonic acid of the air, uniting with the lime, solidities it, to- gether with whatever may be in mixture with it. But, let us collect together this white solid, and examine it ; and we will soon be convinced, that it possesses but little activity, and that, if mixed with sand, it will not solidify with any force, but will constitute little else than a me- chanical mixture. But, let us fake some clear, dry sand, and moisten it with a strong lime water, clear and colorless, and collect the moistened sand into a compact mass, and, in a short time, it will become solid and hard. Eveiy grain of sand will be enveloped in carbonate of lime, and all will be cemented firmly together. Break up this mass, as the mason's tender does with the old mortar- bed, and remix it; and you might as well