80 BLACK CHALK. HONE. 
burned and coarsely ground, is used instead of sand in 
the making of a solid and impermeable mortar or 
oement; for the parts of buildings that are covered with 
water. 
121. BLACK CHALK, or DRAWING SLATE, -is an 
earthy substance, of slaty texture ; generally of a greyish, 
sometimes a bluish black' colour. 
It is soft and smooth to the touch, and, in handling, stains the 
fingers. 
To crayon painters, and other artists, black chalk is 
a very useful article. Considerable quantities of it are 
imported from France, Spain, and Italy.. The best is 
brought from Italy. This is more free from gritty par- 
ticles, more firm and compact in its texture, and in its 
touch much smoother than the chalk of any other coun- 
try. It contains somewhat more than one-tenth part of 
its weight of charcoal. When prepared for use, it is 
cut into square pieces, which are sometimes enclosed 
ia wooden cases, like black lead pencils. These pen- 
cils are said to become dry, hard, and unfit for use, by 
long keeping. To preserve them in greatest perfec- 
tion, they should be kept in a moist place. Some artists 
prefer pencils that are made of the chalk finely ground, 
mixed with a certain proportion of gum water, and cast 
in moulds. Care should be taken not to put too much 
gum, as the pencils will not, in such case, leave any 
mark on the paper. 
Drawing slate is sometimes used as a black colour 
for painting. For this purpose it is pounded or ground, 
and then mixed with oil or size, according to the kind 
of work for which it is required. When black chalk is 
strongly heated, it loses its colour, and assumes that of 
a reddish grey. 
122. HONE, or WHET SLATE, is a well-known kind of 
stone, of wmeivhat slaty texture, and generally of dull zchite, 
or greenish grey colour. Its surface is smooth, and feels unc- 
tuous to the touch. 
