“* Hardness.—All the various corals examined were superior in hardness to calcareous
spar or common marble, and not inferior to Arragonite; while some were as hard as
Apatite or crystallized phosphate of lime ; or according to the scale used by mineralo-
gists, the usual hardness will be expressed by 4, though in a few instances as high as 5,
Using an iron mortar in the earlier trials, the iron pestle was roughened and cut under
the resistance of the angular masses of coral, to a degree quite remarkable considering
the nature of the substance operated on, So much iron was communicated to the powder
from this source, that recourse was had to a mortar of porcelain, and even this was not
proof against wear, the porcelain pestle being pitted by the repeated blows. The more
porous species, of course, were crushed with less difficulty ; and this was especially the
case with the species of Porites.
“ Specific Gravity.—The specimens were reduced to fine powder before trying the spe-
cific gravity, as the porous character of the coral would otherwise interfere with obtaining
correct results. Considerable variation will be observed in the following table. The
numbers correspond to the catalogue on the preceding page.
Specimens. Sp. Grav. | Specimens. Sp. Grav. Specimens. Sp. Gray.
No | © Barr © |} Nov20 2917 No. 31 2-688
3 | 9.732 99 9-564 33 2-500
4 | 2-564 23 2-353 34 2.500
9 2-421 25 | 2-578 Meand. rustica! 2571
10 2-105 26 2-584 Shell of t BRS
~ 2-857

12 2-427 27 2-740 Chama.
| |


32


126 ZOOPHYTES.
