100 MARBLE. 
mass is thereby loosened, and falls down before morn- 
ing. 
The harder and more compact kinds of chalk are cut 
into blocks, and used as building stones. When burned 
and formed into lime, chalk becomes an excellent mor- 
tar : nearly all the houses in London are cemented with 
chalk mortar. It is also used as lime in agriculture. 
As it readily imbibes water, it is used by starch-makers, 
chemists, and others, to dry precipitates upon. With 
isinglass or the white of eggs it forms a valuable lute or 
cement. By artists it is in request for the construction 
of moulds to cast metals in ; and by carpenters and 
others, as a material to mark with. Chalk is one of the 
most useful absorbents that are employed in medicine : 
it likewise gives name to an officinal mixture, to a pow- 
der, and a potion. 
When pounded and cleared from gritty particles, it 
has the name of whiting. In this state it is used for the 
cleaning and polishing of metallic and glass utensils ; 
for whitening the ceilings of rooms, and numerous other 
purposes. Spanish white is the same substance cleansed 
with peculiar care ; and the Vienna white, which is used 
by artists, is perfectly purified chalk. 
142. MARBLE is a compact and close-grained lurid of 
Limestone ; so hard as to admit of being polished. It is this 
quality which principally distinguishes it from other calcareous 
substances. 
Although nearly all the numerous kinds of marble 
may be burned, and thus converted into quick-lime, 
their use in ornamental architecture, &c. is so impor- 
tant as, in general, to prevent their application to the in- 
ferior purpose of mortar. Marble has been known from 
a very early period. The Book of Esther, in the Old 
Testament, describes the palace of Ahasuerus to have 
had " pillars of marble," and the pavement of " red, 
and blue, and white, and black marble." 
It would be impossible, in an elementary work like 
the present, to describe, or even to enumerate, all the 
different kinds of marble which were known to the an- 
