USES OF GLUE.
An inquiry into the various technical uses of glue must be of interest
to the manufacturer so as to enable him, when acting, as is frequently
the case, as salesman, to know to whom to offer his product; and also
to learn what special demands he has to satisfy, as not every glue
is adapted to every purpose, different qualities being required for
special uses.
_Glue as a joining medium._ In Chapter I, treating of the nature of
glue, special attention has been drawn to the fact, that the adhesive
power of glutin is greater than that of chondrin; and that glutin
obtained from skin and tendons possesses still greater adhesive power
than the product from bones. This is the reason why good sound glue
made from scraps of skin is preferred by those artisans who may be
considered the principal consumers, such as cabinet-makers, carpenters,
turners, instrument-makers, wood-carvers, carriage-builders,
brush-manufacturers, bookbinders, paper-manufacturers, etc., all
of them requiring glue of the greatest possible adhesive power. It
must, however, by no means be understood that a good quality of bone
glue cannot be used for the same purposes; because much bone glue of
excellent quality and at a low price is brought into the market by
manufacturers of animal charcoal and bone meal, and is used in glueing
wood, etc.
Glue suitable as a joining medium for the above purposes should be of
an amber or brown-yellow color, transparent or translucent, clear, dry
and hard, and show a glassy fracture which should not be brittle, but
somewhat elastic. Placed in cold water it should swell up and absorb
as much of it as possible without actually dissolving, even if it
remains there for 48 hours. The supernatant water should be free from
a putrid odor and contain but a small quantity of foreign substances
in solution. Such glue passes into solution at 122° F., and dissolves
entirely on heating to 144.5° F. Heating to a higher temperature should
be avoided.
_Glue as a binding agent._ Glue solution is used for bind-together
pulverulent substances, such as mineral colors in the manufacture of
colored paper and paper-hangings, in painting in distemper, in the
size of the gilder; or it is mixed with plaster of Paris or chalk for
the manufacture of plastic masses which become hard on drying, such
as stucco-work, papier-maché, etc. Generally speaking, it is best to
use only good sound glue for these purposes, though it may sometimes
be possible to utilize defective and cheap qualities without injurious
consequences. For color mixtures, the glue should at all events be
free from acids and alkalies, as they exert a decomposing and altering
effect upon the colors. The gilder should always use the best quality
of glue, as otherwise the work he applies later on to the size will
spoil.
A very large quantity of glue is consumed _in the manufacture of
matches_, and much depends on its quality and drying properties. The
dipping composition for matches containing phosphorus is a bath of
glue of 25 to 50 per cent. strength to which the requisite amount of
an oxidizing agent, like potassium nitrate or chlorate has been added,
kept at a temperature of 100.4° F. The phosphorus is cautiously put
in; it melts, and is stirred to an emulsion, when the sand, glass or
other friction-agent is incorporated. The object of the glue is to
protect from oxidation, without diminishing the sensitiveness. Glue is
also used as the binding material in the heads and rubbers of safety
matches.
_Book binders_ require for the better classes of work a glue which
should naturally be pale and strong, and without marked odor. Some
inferior glues which have been chemically bleached turn almost black in
the pot, owing to the bleaching agent not having been properly removed
or neutralized.
Sand, glass and emery papers and cloths are made by coating the surface
with a thin uniform layer of strong glue, and sifting the powder evenly
on.
_Glue in sizing._ The principal object of sizing goods is to impart to
them a certain degree of stiffness, to give them a nice appearance and
a good feel.
As glue would injure the color of white goods, it cannot be used for
sizing them, but, on the other hand, much is employed for preparing
size for the use of hat and cloth manufacturers, weavers, etc. Before
the introduction of the paper machine and invention of rosin glue,
animal glue was exclusively used for sizing paper, but at the present
it is only used for sizing paper manufactured from rags, and for
pasteboard, and also by manufacturers producing drawing paper sized
with animal substances. The paper, after leaving the machine, is passed
through a glue solution and then dried in the air.
For actual sizing purposes good and fine varieties of glue are only
used, or sometimes the manufacturers prepare their own size by boiling
to glue dried calves’ heads, or rabbit skins deprived of their fur,
scraps of parchment, etc. For cheap woollen hats, glue is used in place
of shellac. The cloth manufacturer procures his glue mostly in the form
of a jelly. This variety of glue deserves special attention and the
mode of preparing it will be referred to later on.
_Glue for culinary and medicinal purposes._ The use of glue for these
purposes is based upon three properties:
1: Upon its power of coagulating and inclosing while in this state,
substances mechanically dissolved and finely divided in a fluid, which,
being specifically as heavy as the fluid itself, render the latter
turbid and cannot be got rid off by settling. The glue in this case
acts as a clarifier.
Large quantities of isinglass and gelatine, specially prepared for
the purpose, are used for clarifying and fining beer, wine and other
liquids, as well as for preparing jellies. The material to be used for
jellies and other culinary purposes must, of course, be colorless and
entirely free from odor. Jellies are made palatable by flavoring with
spices, sugar, essences, etc., before congealing, A vegetable gelatine,
Agar-Agar, which will be referred to later on is now brought from
China, and being cheaper and perfectly free from odor, has become quite
a competitor with isinglass and gelatine.
Prior to the introduction of Liebig’s and other beef extracts, bouillon
tablets, consisting of a mixture of bone-jelly, meat broth, extract
of pot herbs and flour, were largely used. One hundred and ten pounds
of meat repeatedly boiled yield five pounds of bouillon tablets. A
good meat broth, though not equal to that from Liebig’s or other meat
extracts, is obtained from these tablets by the addition of thirty
times their weight of water.
If glue be dissolved in water, it gelatinizes at the ordinary
temperature, and if the solution be mixed with other fluids, for
instance, meat broth, fruit juices and essences, which in the form of
jelly are to serve as food, it effects their solidification.
Glue acts as a healing agent by preventing the access of air to
wounds. Court plaster is prepared from gelatine. When cabinet-makers
cut themselves, they apply glue to the wound with the best success.
In hospitals a compound of gelatine and glycerine is used as the
best means of closing wounds, the same compound having also been
successfully used for preserving articles of food such as eggs, fruit,
and even meat.
Every good quality of glue can be used for the above purposes.
Medicines of a disagreeable taste are frequently inclosed in gelatine
capsules, so that they can be taken without causing inconvenience to
the patient. The use of these capsules has grown to such an extent as
to form a special branch of industry. The mode of manufacturing them
will be described later on.
_Glue for elastic masses and as a partial substitute for rubber._ Glue
mixed with glycerine forms an elastic mass resembling rubber. The
same effect can be produced by an addition of molasses. This elastic
mass, the preparation of which will be described later on, is of great
importance for the manufacture of printers’ rollers, for moulds, etc.
Some manufacturers prepare the mass ready for use, so that the printer
or lithographer need only remelt it, and cast it in a mould.
Glue is of great importance in photolithography as, mixed with chromium
salts, it is the only known means of transferring a photographic
negative to the stone. In photography, gelatine is used for negative
pictures upon glass. For the manufacturer of casts of plaster of Paris
or cement, this glue mass, which is generally used without an addition
of glycerine, is indispensable for making moulds which are much
undercut.
Glue mixed with glycerine may be used as a substitute for rubber in
manufacturing elastic toys, such as dolls’ heads, animals, etc. For
these purposes it is advisable to select glue which forms a very solid
jelly, even if it possesses but little adhesive power, pure bone-glue
being the best.
Glue mixed with glycerine (1 part glue, 1 part glycerine) is used as
hectograph mass for the transfer of matter written with concentrated
solution of aniline color.
_Glue for fancy articles._ Great progress has been made in the use of
glue and gelatine in the manufacture of fancy articles.
The best known of all these products are perhaps the gelatine foils.
They form thin, transparent sheets, brilliantly colored, and are used
for printing sacred images, visiting cards, labels, etc.
Gelatine veneers were first shown at one of the Paris International
Exhibitions. They consist of sheets varying in thickness, which
have been deprived of their translucency by an admixture of colors
in imitation of various crystallization of salts, and such stones
as lazulite, malachite and avanturine. Glue imitations of mother of
pearl, tortoise shell, and ivory were shown which closely resembled the
genuine articles. These veneers have been largely introduced in the
manufacture of fancy articles, cabinet ware, buttons, etc. The most
brilliant use to which they have been put is in the manufacture of
fans, for which ivory and tortoise shell were formerly used, and there
are perhaps few ladies that are aware that these glittering toys are
manufactured from horse bones from the knacker’s yard.
The successful introduction of gelatine veneers was soon followed by a
substitute for horn in general, and combs, buttons, snuff-boxes, and
hundreds of other fancy articles have been manufactured from these
imitations.
In the foregoing statement only some of the principal uses of glue have
been enumerated, and there can be no doubt that with an increase in the
knowledge of its nature and properties, a wide field is still open for
progress in this industry.