The _trowel_ is the first and most indispensable of these tools. It is a thin, flat, lozenge-shaped blade of steel, fixed into a handle. It is with the trowel the workman takes up and spreads the layer of mortar put between each brick, and with it he also _cuts_ the bricks so as to fit into any corner, or to adapt them to some particular form; and to enable it to cut, or rather chip, such a hard substance as burnt clay, and yet not break, it is necessary that the blade should be of well-tempered hard steel. The _square_ and _level_ are made of wooden rules put together; the first at a true right angle, to enable the bricklayer to set out his walls correctly perpendicular to each other,--the second is framed like a ⟂, with a plummet hanging in a slit in the upright piece; now, as the two rules are correctly perpendicular to each other, it is clear that when the first is set by means of the plumb-line perpendicular to the horizon, the other will be truly horizontal. By means of this important instrument, the workman guides his work, so that the wall he is building shall be upright, and the courses of bricks composing it horizontal. By means of this important instrument, the workman guides his work, so that the wall he is building shall be upright, and the courses of bricks composing it horizontal. _Mortar_ is the name given to the composition with which the bricks are put together. Good mortar should be made of newly-burnt quicklime from grey limestone, and of clean river-sand, in the proportions of one-third lime to two-thirds sand. The lime is _slaked_ by pouring a little clean water on it, and when it falls to powder by the chemical action, the sand is added gradually, and the whole well mixed up with a spade, more water being used till the mass is of the proper consistence for spreading easily. As the adhesion of the bricks depends on the mortar being applied before it begins to _set_ or harden, it should not be mixed till it is to be used. When these simple precautions are attended to, the mortar becomes in time as hard as stone, and the brick-work constructed with it is nearly as indestructible. It was by taking this care with their materials that our forefathers built walls that have stood uninjured for centuries. In some of the cheap common buildings of the present day, mortar is too often made from lime which has been so long from the kiln, that it is nearly reconverted into a hydrate, and has lost the chemical quality which renders it valuable; the sand, too, is taken from the road with all its impurities, and the water from the nearest kennel. With such materials a mass of mortar is made, and suffered to stand for several days before it is used; the consequence is, that such buildings are neither safe nor durable.