In various processes, cements of different descriptions are required
for a variety of purposes. The common cement used in building, which
is called mortar, is made of sand and quicklime mixed with water.
Roman and Portland cements consist of certain kinds of clay burnt
and ground. Plaster of Paris forms a useful cement, it is to be
mixed with water to the consistence of cream, and it hardens in a
few minutes. Glue is an invaluable cement for wood and many other
purposes, it also joins any kind of broken glass or china that will
not have to be subjected to much wetting. Shellac dissolved in spirit
is a useful cement; and isinglass, dissolved in weak spirit, and
having some gum ammonicum added to it, forms the “diamond cement” for
uniting china. China and glass which require to be much wetted, are
best united by being made very hot and having the broken edges rubbed
with a piece of shellac, this melts on them, and forms, while hot,
a sort of cement; if they be immediately applied and pressed firmly
and accurately together, and then permitted slowly to cool, they will
unite so as to be almost as strong as before breaking.