In the preceding table, the cements had, in all cases, six months to indurate, and the mortars (except in the second case) from six months' to seventeen months' induration.

Examples of very old and good, lime and sand mortar, may be found occasionally in good brickwork—such as that of the Roman amphitheatre at Pozzuoli, for example; or in rubble masonry, where the bond of the stone with lime mortar is peculiarly strong, as with the oolitic building stones, and limestones generally, and with a few sandstones and porous traps, in which the adhesion, of the indurated mortar, becomes fully equal to its cohesion, and both rise above 50 lbs. to the square inch, for forces suddenly applied.

In determining the mean specific gravity, of brickwork and rubble masonry, the proportion of mortar, to the brick or stone in a given volume, may be taken at from ${\displaystyle {\tfrac {1}{12}}}$th to ${\displaystyle {\tfrac {1}{7}}}$th, according to the goodness of the work.

No.	Conditions of Fracture.	Value of ${\displaystyle \scriptstyle {\mathrm {L} }}$
1	Apennine limestone, broken through the stone	225
2	Cretaceous limestone, ditto ditto	154
3	Apennine limestone rubble masonry, of best quality, broken through the joints	52
4	Apennine limestone rubble masonry, of inferior quality, broken through the joints	30
5	Apennine limestone, rubble masonry of best quality, mortar not indurated	3.9
6	Argillaceous rubble masonry of the Murgia (Apennine marl rocks), best quality, with indurated mortar	55
7	Best Italian or Roman brickwork in mortar	63
8	Inferior brickwork in mortar	30
9	Brickwork, the mortar not yet indurated	2.5
10	Rubble masonry of tufa and mortar, good, with mortar indurated	87
11	Rubble masonry of Travertino, or Peperino, and mortar indurated	51