Glue is made from the clippings of hides or any other refuse of
skins, horn shavings, bones, &c. All these substances are piled up
in a boiler having a second bottom within, perforated with holes,
and kept from the true bottom by short feet; this arrangement is
to prevent the substances boiled from burning at the bottom of the
boiler. After many hours’ boiling the liquid is tested, and if it
“sets” into a sort of jelly readily, the liquor is drawn off into
another boiler, where it is kept warm, that it may not set till used.
From this boiler it is strained through flannel into square wooden
boxes, having ridges at the bottom dividing them into squares (to
direct the workmen where to cut the glue when cold); these boxes are
set apart, and when the contents have become cold and set into a
firm jelly, a knife is passed between the sides of the box and its
contents, and the glue turned out in a large solid square. This is
now cut by means of a wire with a handle at each end into squares
of about eight inches each way and an inch thick; these are now
placed on nets made of cord fixed in frames one above another in a
“drying-room,” which is open to the air at the sides, and able to
be closed up in case of wet weather. In this room the glue dries up,
shrinks, and hardens, until it is quite brittle; the marks of the net
can be seen on every square of glue.
Size is the same as glue, but instead of being dried it is put into
small barrels. Two qualities of size are made, single and double
size. It is much used by whitewashers, paper-hangers, and others,
but for any purpose requiring good size, it may be made by soaking
isinglass or gelatine in cold water till it is softened, and then
standing the vessel in boiling water till it is dissolved; this
produces a jelly nearly pure. A cheaper kind of size, almost as pure,
may be made by boiling clippings of clean parchment till they are
dissolved, and straining off the solution. Gelatine is the same as
glue, but made of materials that are clean and fresh. Isinglass is
the “sound” or swimming-bladder of the sturgeon, cleaned, dried,
and cut up into fine shreds.