So as to ascertain whether lime is hydraulic or not, after the mortar has been mixed, take a small quantity of the mortar, sufficient to make a ball about 2 in. in diameter, and also a pat (on a piece of glass or a plate) about 4 in. diameter and 1/2 in. thick. Let these remain until just set, then place carefully under water. If the lime is hydraulic, they will become harder and be quite firm by the next day, with the exception, possibly, of the outside skin; if not hydraulic, the sample pat and ball will be found to have fallen to pieces.