B.--Details of internal
structure as seen by the microscope.
C and D.--Crystals of anhydrous Lime obtained artificially. C.--Crystals
seen under the microscope in the natural light. D.--Crystals seen under
the microscope in polarized light.
The phenomenon is explained by the slow carbonization of the anhydrous
lime under the influence of the air; the external layers passing to the
state of carbonate of lime or Iceland spar, which, as well known, has
great influence on polarized light. This transformation, which takes
place without disturbing the crystalline state, does not lead to any
general modification of the form of the crystals, and the final product
of carbonization is a cubic form known in mineralogical language as
_epigene_. As the molecule of spar is entirely different in form
from the molecule of lime, the form of the crystal is not absolutely
preserved, and there are observed on the edges of the epigene crystal
certain grooves which correspond with a loss of substance. These grooves
are quite visible, for example, on the crystal to the left in Fig. D.
Up to the present time anhydrous lime has been known only in an
amorphous state. The experiment which has produced it in the form noted
above would doubtless give rise to crystallized states of other earthy
oxides likewise, and even of alkalino-earthy oxides.
COCCIDAE.
[Footnote: A paper recently read before the California Academy of
Sciences.
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