DIFFERENT VARIETIES OF GLUE AND THEIR PREPARATION.
Besides the broadly-distinguished forms of skin-and bone-glue, the
trade recognizes a large number of varieties, distinguished either by
their value or their fitness for special purposes.
_Joiner’s Glue._—This variety is without doubt the oldest in use and
most in demand, and its principal requisite is its great adhesive
power. It is used for joining wood, leather, paper, etc., and varies
very much in quality and price.
The best variety is prepared from scraps of hide and skin. A light
color not being especially demanded, there existing rather a prejudice
in favor of a dark-colored article, waste of cattle and horse skins and
tendons can be used for its manufacture.
Joiner’s glue, which is generally preferred in thin cakes, is chiefly
manufactured in regular glue factories, though to be able to compete
with the bone-glue turned out by the large establishments, the
glue-boiler generally mixes skin and bone-glue, and is thus enabled to
turn out a tolerably good quality. The price paid for the different
varieties of joiner’s glue varies very much, being generally higher in
winter than in summer, and is frequently more regulated by the external
appearance of the article than by its actual value. Glue without gloss,
very much warped and of a very dark color, may, notwithstanding its
faulty appearance, possess excellent qualities.
Nothing need be said about the manufacture of joiner’s glue, since what
has been said about the manufacture of glue in general suffices for the
purpose.
_How to make and use glue._ Break the glue into small pieces, put it
into an iron kettle, cover it with water, and allow it to soak twelve
hours; after soaking boil until done. Then pour into a box which can be
covered air-tight; leave the cover off until cold, then cover up tight.
As glue is required, cut out a portion and melt in the usual way.
Expose no more of the made glue to the atmosphere for any length of
time than is necessary, as the atmosphere is very destructive to made
glue.
All glue, as received from the factory, requires the addition of water
before it will melt properly, and every addition of water (while
the glue is fresh made) will, up to a certain point, increase its
adhesiveness and elasticity. Some glues will bear more water than
others, but all will bear more water than usually falls to their share,
and that, too, with a greater improvement in the quality of the work.
For glue to be properly effective, it requires to penetrate the pores
of the wood, and the more a body of glue penetrates the wood the more
substantial the joint will remain. Glues that take the longest to dry
are to be preferred to those that dry quickly, the slow-drying glues
being always the strongest, other things being equal. Never heat made
glue in a pot that is subjected to the direct heat of the fire or a
lamp. All such methods of heating glue cannot be condemned in terms too
strong. Do not use thick glue for joints or veneering. In all cases
work it well into the wood in a manner similar to what painters do
with paint. Glue both surfaces of your work excepting in the case of
veneering. Never glue upon hot wood, as it will absorb all the water in
the glue too suddenly, and leave only a very little residue, with no
adhesiveness in it whatever.
_Holding power of glue._ 1. Glue exerts a far greater hold on surfaces
of wood cut across the grain than on those that have been split, or cut
with the grain.
2. When two surfaces of split wood are laid together, the hold of the
glue is the same whether the fibres are laid parallel or crosswise to
each other.
3. The holding power of glue on different woods estimated in
kilogrammes per square centimeter (0.155 square inch) is as follows:
Cut across the grain. Split.
Beech, 155.55 (342.21 lbs.) 78.83 (173.42 lbs.)
Hornbeam, 126.50 (278.30 lbs.) 79.16 (174.15 lbs.)
Maple, 87.66 (192.85 lbs.) 63.00 (138.6 lbs.)
Oak, 128.34 (282.34 lbs.) 55.16 (121.35 lbs.)
Fir, 110.50 (243.10 lbs.) 24.16 (53.15 lbs.)
_Cologne glue._ The variety of glue known under this name is prepared
from selected scraps of hide and skin, and is consequently very pure,
and possesses great adhesive power. It is of a light-brown color,
and comes into commerce in short thick cakes of great hardness. It
is an excellent quality of glue, and is preferred to all others by
bookbinders, workers in leather, etc. There are many imitations of this
variety, bone-glue being frequently sold as Cologne glue.
The genuine article is manufactured from refuse of hide, which, after
liming, is carefully bleached in a bath of chloride of lime, the
concentration of which depends on the darker or lighter color of the
glue-stock. For 220 lbs. of glue-stock, it is generally customary to
use 1 lb. of chloride of lime mixed with sufficient water to cover the
stock.
After thorough impregnation of the glue-stock, which generally requires
about half an hour, add sufficient hydrochloric acid to impart an acid
taste to the bath of chloride of lime. To be able to mix the mass
thoroughly, it is best to use a vat provided with a stirring apparatus.
After allowing the acid to act for a quarter of an hour, remove every
trace of it by careful washing.
To obtain a jelly as clear as possible, the gelatinous liquor is drawn
off as soon as the thin portions of the glue-stock and the outside of
the thicker ones are dissolved, they being more thoroughly bleached
than the rest. The residue is worked into darker glue.
_Russian glue._ This variety is of a dirty white color, and, like
Cologne glue, is brought into commerce in short, thick cakes. Its color
and opaqueness are imparted to it by an addition of 4 to 8 per cent. of
white lead, chalk, zinc white, or permanent white (sulphate of baryta).
It has been claimed that the superior adhesive power of Russian glue
is due to this addition of mineral substances, but the results of many
experiments fail to substantiate this claim. In case the glue turns
out turbid, it may be of advantage to make it opaque by an addition of
coloring matter, but the quality of the glue remains unchanged. The
best time to add the coloring matter is shortly before drawing the
glue-liquor from the clarifying vats into the cooling boxes, as the
jelly is then of sufficient consistency to prevent the substances from
settling on the bottom. Skin-glue, as well as bone-glue, is sold under
the name of Russian glue.
Quite a considerable quantity of Russian glue brought into commerce in
the form of brownish-white sheets is prepared from bones, the latter
being degreased by boiling, steaming or extraction, and the solution of
the mineral constituents effected by means of hydrochloric acid. The
treatment with acid is, however, continued only till the bones commence
to become soft and flexible. The solution of phosphates is then drawn
off, and the softened bones are washed and in the usual manner worked
to glue.
By this incomplete treatment with hydrochloric acid, a certain quantity
of the phosphates remains in the cartilage and is inclosed in the
glue prepared from it, the finished product acquiring thereby a dirty
whitish color, which is by many considered an evidence of its quality.
This mechanical admixture of phosphates, however, does not affect the
adhesive power of the glue, neither increasing or decreasing it. Such
white and opaque glue is manufactured to answer the demand in certain
quarters of the trade, and, as above mentioned, heavy white substances
are often intentionally incorporated with skin glue, as well as bone
glue, to give it the appearance of Russian glue. These heavy powders
add to the weight of the product, though when incorporated with it in
small quantities do not injure its adhesive power, but large quantities
render the product weaker.
_Patent glue._ This term is applied to an indefinite number of
preparations, but particularly refers to a very pure variety of bone
glue of a deep dark-brown color not showing net marks. It is very
glossy, and swells up much in water. To satisfy the demand for thick
cakes, they must be cut from very concentrated jelly to insure their
drying.
_Gilder’s glue_ is found in commerce in very thin, pale yellow cakes
tied up in packages weighing about 2 lbs. each. It is a variety of skin
glue bleached with chloride of lime, and dissolves with difficulty in
water. The first runnings from the boiler are used for its manufacture.
A very superior article of gilder’s glue is obtained by cutting
rabbit skins into fine shreds and boiling in water, then turning the
mixture into a basket through which the liquid passes, leaving the
refuse behind. About 100 grammes (3.52 ozs.) of sulphate of zinc and
20 grammes (0.705 oz.) of alum are then separately dissolved in pure
boiling water and poured into the first-mentioned liquid, and the whole
well stirred together while hot. The mixture is then passed through a
sieve into a rectangular box, in which the jelly remains twenty-four
hours in winter, or forty-eight in summer. The solid mass is taken from
the box, cut into slices of proper thickness, and dried upon nets.
_Size glue and parchment glue_ are manufactured in the same manner.
Both are skin-glues, and can be readily produced by following the
directions given for the manufacture of skin-glue.
_Paris glue_ is used for sizing. It is brown, opaque, and almost always
soft. Being very hygroscopic, and imparting a suitable flexibility to
the felt, it is better adapted for hatter’s use than any other variety.
For its manufacture only the generative organs, or the thick tendons
of the legs of cattle and horses, are used, or other waste and fleshy
parts, and substances mixed with small bones, which, if thoroughly
cleansed, might yield a good quality of glue, but are intentionally
transformed by too long-continued boiling, whereby the gelatinous
solution is largely deprived of its adhesive power, and yields a
hygroscopic product.
_Liquid Glues._ These are chiefly combinations of glue with some
ingredients added to destroy the gelatinizing property and yet not
impair its adhesiveness. They remain for a long time clear and syrupy,
and are used for a variety of purposes. Below are given a few receipts
for such glues.
1. Dissolve 38 parts of glue in small pieces in 100 parts of acetic
acid. Solution is promoted by exposing the vessel to the sun or placing
it in hot water.
2. Dissolve 50 parts of light-colored glue in 50 parts by weight of
hot water, in which 14 parts of fused magnesium chloride have been
dissolved. The solution on cooling does not gelatinize, but remains
syrupy, the density varying according to the quantity of water used. In
the preparation of printing inks it can be used as a substitute for gum.
3. Dilute 10 parts of strong phosphoric acid with an equal weight of
water, and then gradually add 4 parts of ammonium carbonate in the dry
state. When the effervescence has subsided, add a further 5 parts of
water and warm on the water-bath or steam-chest to 158° F. Now add 20
to 40 parts of glue, according to the consistency required, and stir
until all is dissolved. Cool.
4. Dissolve 20 parts of glue in an equal weight of hot water, then
cautiously pour in, stirring constantly, 4 parts of strong nitric
acid, warm until the nitrous fumes have been driven off, filter, if
necessary, through fine shavings, and allow to cool.
5. Dissolve 3 parts of glue in small pieces in 12 to 15 parts of
saccharate of lime. By heating, the glue dissolves rapidly and remains
liquid, when cold, without loss of adhesive power. Any desirable
consistency can be secured by varying the amount of saccharate of lime.
Thick glue retains its muddy color, while a thin solution becomes clear
on standing.
The saccharate of lime is prepared by dissolving 1 part of loaf sugar
in 3 parts of water, and after adding one-fourth part of the weight of
sugar of slaked lime, heating the whole to between 149° and 185° F.,
and allowing it to macerate for several days, shaking it frequently.
The solution, which has the properties of mucilage, is then decanted
from the sediment.
The solution of the glue in saccharate of lime is readily accomplished,
even old gelatine, which has become insoluble in water, dissolving
without difficulty. This variety of liquid glue possesses great
adhesive power, and admits of many uses.
6. Dissolve 8 parts of glue in 16 parts of hot water, then add ½ to 1
part of hydrochloric acid, and 1½ parts of sulphate of zinc. Keep the
mixture for 8 hours at 158° F., then filter through fine shavings, and
allow to cool.
_Steam glue._ Under this name several varieties of liquid glue are
brought into commerce. They are prepared as follows:—
1. _Russian steam-glue._ 100 parts of a good quality of glue, 100 to
110 parts of warm water, and 5.5 to 6 parts of commercial nitric acid
of 36° B.
2. _Pale steam-glue._ 100 parts of glue, 200 of water, and 12 of nitric
acid of 36° B.
3. _Dark steam-glue._ 100 parts of glue, 140 of water, and 16 of nitric
acid of 36° B.
Soak the glue in cold water, then pour the necessary quantity of warm
water over it, and heat gently on a water-bath until all the glue is
dissolved. Next add gradually the nitric acid with constant stirring,
and to the Russian steam-glue 6 parts of finely pulverized sulphate of
lead, which will impart to it the white color.
_Chrome glue._ This preparation is very permanent and durable. To
prepare it add to a moderately concentrated solution of 5 parts of
glue 1 of dissolved acid chromate of lime, this salt being considered
better for the purpose than the bichromate of potash usually used. The
glue thus prepared becomes, after exposure to the light, insoluble
in water in consequence of a partial reduction of the chromic acid.
This preparation can be used for cementing glass articles, liable to
be exposed to boiling water, the treatment being the ordinary one of
applying the glue to both surfaces of the fractured object, and then
binding them together until dry, and exposing them for a sufficient
length of time to the light, after which boiling water will have no
effect upon them. It is suggested that this preparation is better
adapted to cementing the covers on glass slides than any now in use.
The same preparation can be applied for making fabrics water-proof,
especially sails, awnings, etc., where no great flexibility is
required. Two or three applications of the glue, either by immersion
of the object in it, or by the use of the brush, will answer the
purpose. Roofing paper is also rendered impervious, even when exposed
to long-continued rains.
_Glue for attaching leather to metal._ A method of affixing leather to
metal, so that it will split before it can be torn off, consists in
digesting a quantity of nutgalls, reduced to powder, in eight parts of
distilled water for six hours, and filtering it through a cloth; then
dissolving one part by weight of glue in the same quantity of water,
and allowing it to remain twenty-four hours. The leather is moistened
with the decoction of nutgalls and the solution of glue applied to the
metal, previously roughened and heated. The leather is then laid upon
it, and dried under pressure.
_Glue for leather, paper, etc._ The following process affords an
unusually adhesive paste, adapted to fastening leather, paper, etc.,
without the defects of glue, and if preserved from evaporation in
closed bottles will keep for years. Cover 4 parts, by weight, of glue
with 15 parts of cold water, and allow it to soak for several hours;
then warm moderately till the solution is perfectly clear, and dilute
it with 65 parts of boiling water, intimately stirred in. Next prepare
a solution of 30 parts of starch in 200 of cold water, so as to form
a thin homogeneous liquid free from lumps, and pour the boiling glue
solution into it with thorough stirring, and at the same time keeping
the mass boiling.
_Glue for parchment paper in making sausage skins._ The supply
of intestines soon being exhausted by the enormous quantity
of pease-sausages manufactured for the German army during the
Franco-German war, the necessity arose for a substitute. This consisted
of a tube of parchment glued together. Millions of these tubes from Dr.
Jacobsen’s factory were tested by the government, and found to answer
the purpose admirably. They were even boiled for hours without either
the glued seam or the paper itself being injured by the operation.
The secret of the composition of the glue employed for fastening
the parchment paper seems to be well kept, but the one given in the
following is equal to it in all respects, if not indeed identical:
Add to one quart of a good adhesive solution of glue ¾ to 1 oz. of
finely powdered bichromate of potash. Warm the mixture slightly on a
water-bath when about to use it, and before applying it moisten the
parchment paper. The latter, when glued with this preparation, as in
the formation of the small cylinders for sausages, must be rapidly
dried on a hurdle, and then exposed to the light until the yellow glue
becomes brownish. The cylinders are then slowly boiled in a sufficient
quantity of water to which two or three per cent. of alum has been
added, until all the chromate is dissolved out, and they are then
washed in cold water and dried, and will look very inviting, especially
if white glue has been used. A similar result may be reached by using
a concentrated solution of cellulose in ammoniacal oxide of copper.
Thus if cylinders of unsized paper are formed with this paste, and
when thoroughly dry drawn through a parchmentizing solution (a cooled
mixture of 2 volumes of fuming sulphuric acid and 1 volume of water),
they will be beautifully parchmentized, and after the neutralization
of the acid, washing, etc., it will present a striking resemblance to
natural intestines.
_Tungstic glue._ This preparation offers an acceptable substitute for
hard India rubber. It is made by mixing a thick solution of glue with
tungstate of soda and hydrochloric acid, by means of which a compound
of tungstic acid and glue is precipitated, which, at a temperature of
86° to 104° F., is sufficiently elastic to admit of being drawn out
into very thin sheets. On cooling, this mass becomes solid and brittle,
and on being heated is again soft and plastic. It can be used for all
purposes to which hard rubber is adapted.
_Indestructible mass for the manufacture of ornaments, toys, etc._ A
mass, which is to have the hardness of horn, consists of 50 parts of
glue, 35 of wax or rosin, 15 of glycerine and the required quantity of
a metallic oxide, or mineral color. A soft mass consists of about 50
parts of glue, 25 of wax or rosin, and 25 of glycerine. The glue is
melted in the glycerine with the assistance of steam, and the wax or
rosin added. The latter in melting mixes with the glue and glycerine,
and finally the mineral color is added. The mass is poured in a liquid
state into moulds of plaster of Paris, wood, or metal. The degree of
hardness of the mass is increased by an addition of 30 to 35 per cent.
of zinc white, or other mineral color, according to the color the
article is to have.
_Compound for billiard balls._ Allow 80 parts of Russian glue and 10
parts of Cologne glue to swell up in 10 parts of water; then heat over
a water-bath, and when dissolved, add 5 parts of heavy spar, 4 parts
of chalk and 1 part of boiled linseed oil. Of a portion of the mass
form small sticks, dip them in the remainder, and allow the adherent
portion to dry, and repeat this process until a crude ball has been
formed. This is placed in a dry room for three or four months, and when
thoroughly dry, it is turned. The finished ball is placed in a bath of
sulphate of alumina for one hour, dried, and polished like an ivory
ball.
_Coloring glue._ Common black or dark glue, while possessing all the
adhesive and other essential qualities of fine colored glue, has
heretofore, owing to its color, been confined in its use to such
purposes in the arts where color was not essential.
The object of the following process, which is the invention of G. J.
Lesser, of Frankfort, Germany, is to color such glue so that it is both
refined and tinted, and may be used for various purposes in the arts.
It is especially applicable in the manufacture of sizing and finishing
compounds for paper hangings, compounds for the manufacture of elastic
rolls, for glue and size compounds for finishing yarns, textile
fabrics of silk, cotton, etc., for the manufacture of calcimines and
wall-coverings, for glue to be used with colored woods, and for all
other purposes where a fine, strong-colored glue is required.
For coloring common black or dark glue take a pound and a half of
liquid extract of lead and mix it into the water in which the glue has
been soaked, as follows: Thirteen pounds of glue, sixty-three and a
quarter pounds of water. Allow the glue to soak for about twenty-four
hours, then dilute it by a slow fire, and when heated gradually pour in
one and a half pounds of the extract of lead and mix it well together.
The extract of lead is a well-known commercial article, and it is well
suited for this purpose; but the inventor does not limit himself to
this particular preparation, as there are a larger number of neutral
and basic compounds of lead that may be so modified as to produce
results similar, if not identical, with the results obtained by the
formula above given. Gelatine may be treated instead of glue.
_Compositions for printing rollers._ All such compositions contain
gelatine or glue. The following receipts are used:
| I. | II. | III.| IV.| V. | VI. | VII.| VIII.
-------------+-----+-----+-----+-----+-----+-----+-----+-----+
Glue | 8 | 10 | 4 | 2 | 32 | 2 | 1 | 3
Molasses | 12 | — | 8 | 1 | 12 | 6 | 2 | 8
Paris white | 1 | — | — | — | — | — | — | 1
Sugar | — | 10 | — | — | — | — | — | —
Glycerin | — | 12 | — | — | 56 | — | — | —
Isinglass | — |1½ ozs.| — | — | — | — | — | —
India rubber| — | — | — | — | 10 | — | — | —
in naphtha
A patent roller composition is thus made: Gelatine 32 lbs. and glue
4 lbs. are softened in cold water and melted in a glue boiler. To
this are added 4 lbs. of glucose, 72 lbs. of glycerine, and 1 oz. of
methylated spirit. The whole is then digested for four to six hours
and cast into rollers. This composition is claimed to be unaffected by
temperature, to retain its elasticity, and not to shrink.
In practice it is found that all these compositions from the cleansing
and remelting become gradually sticky and useless. To partially
overcome this difficulty, formaldehyde is added to the roller
composition, which renders the glue insoluble in water, and thus
prolongs the life of the roller.
_Size._ This product is simply an undried glue and is used, not
for adhesiveness, but as a body for filling porous surfaces, such
as wood or plaster, stiffening and weighting textile fabrics, in
paper manufacture, and as a foundation for oil paints and varnishes.
According to Thomas Lambert, many firms who have a good selling
connection for size, do not go to the expense of erecting clarifying
plant and drying house for treating the glue-liquors, but prefer to
stop the process half way, as it were, and marketing the resulting
product as size. Others, again, with a complete glue plant at hand,
convert only a portion of their liquors into size, to meet trade
demands, the bulk going for the manufacture of glue. Size varies
in quality to suit the requirements of different trades. Cardboard
box-makers prefer a strong skin size, which is manufactured red or
yellow as preferred. A strong yellow size made from bone is used by
calico-printers, paper-stainers, wall-paper manufacturers, and in the
straw-hat and carpet trades.
In the preparation of skin-glue, the first and second liquors are used
for that purpose; the residual mass is then treated with water and
steam, which practically exhausts the gelatinous matter. This, the
third liquor, is used solely for size. During the boiling, samples
are taken at intervals, cooled, and the condition of the jelly noted.
The strength is also taken by the glue meter, which registers the
percentage. At a strength of 8 to 10 per cent. the liquor is run off,
passing through a filter of fine shavings or cloth, to remove any
suspended matter, into a wooden vat fitted with a steam coil, then
heated with a moderate charge of sulphurous acid to bring up the color,
and evaporated to a strength of 36 to 38 per cent., as may be desired,
and then run into casks to jelly. If skin-glue is not made, the three
runnings are used entirely for size.
An outline of a simple process used in an English factory devoted to
making tub-size, as given by Samuel Rideal, may be interesting.
The material is obtained from the tanyard ready limed and freed from
hair, and consists mainly of “faces” of bullocks or cows, the noses
being cut off as food for dogs. It is soaked again in weak lime water
and re-washed, then placed in coppers made of wrought-iron wielded
in one piece, and holding about 10 to 20 gallons, enclosed in outer
jackets of the same material containing water which is kept well
boiling. There are six coppers, about five feet high by three feet in
diameter. The charge of each is about ½ cwt. The material is covered
with water and well stirred with sticks for two hours, the scum and
dross being occasionally skimmed off and thrown away as useless. At the
end the size is ladled on to sieves, from which it runs into cooling
vats, and is filled while moderately hot into clean tubs.
The liquor is clear and of a light brown color for the best XX quality,
and darker for the common. The coolers or setting-backs are of wood or
zinc, and the liquid is not kept hot longer than it can be helped, as
it is liable to turn sour.
Bone-size is, according to Thomas Lambert, prepared as follows: The
bones are first degreased by the naphtha process, and then passed
through the cleanser direct into the glue-boilers and steamed, as in
the manufacture of glue. The resulting liquors are forced up to the
clarifying vats and partially bleached with a current of sulphurous
acid, passing through bag-filters to the evaporating troughs, and
concentrated from 30 to 38 per cent., as required, and then jellied in
casks.
The manufacturer with no benzine or glue plant at his disposal washes
the bones in a revolving drum, and, after crushing, they are fed into
a boiler and subjected to an alternate current of steam and water, the
latter coming from a spray pipe fixed at the top of the boiler. The
liquors are generally drawn in two portions, having a strength of 14 to
16 per cent. of glue. After separating the fat, which is refined and
sold to the soap-maker, the liquors are run into a large wooden vat
about 8 × 6 × 4 feet, fitted with a steam coil, partly bleached with
liquid sulphurous acid, and then boiled down to the required strength.
For a common size the bones are crushed but unwashed, and are fed
direct into the boiler and treated as above. The liquors are not
bleached, and boiled to a strength of about 25 per cent. glue. The
composition of the different grades may be given as follows:
Common size. 25 per cent. glue, 75 per cent. water, etc.
Medium size. 30 per cent. glue, 70 per cent. water.
Best size. 38 per cent. glue, 62 per cent. water.
A concentrated size is now prepared by many manufacturers. It is a
bone-size, and is sold at a Baumé strength at 122° C.
No. 1. 15° Bé. at 122° C., 40.5 per cent. glue.
No. 2. 20° Bé. at 122° C., 44.5 per cent. glue.
No. 3. 25° Bé. at 122° C., 49 per cent. glue.
Under the name of concentrated size also are sold a series of powdered
glues of different qualities. They are the off-color and twisted cakes,
sorted out in the warehouse, and ground to a fine condition by passing
through a mill, and their value is based on the quality of the cake
ground.
Size rapidly ferments and becomes sour and mouldy unless some
preservative is added. Sulphate of zinc is mainly used for this purpose.
_Bookbinders’ Size._—I. Water, 2 quarts; powdered alum, 1 oz.; Russian
isinglass, 2 ozs.; curd soap, 40 grains. Simmer one hour, strain
through linen or a fine sieve, and use while warm.
II. Water, 2 gallons; best glue, 1 lb.; alum, 4 ozs. Prepare and use as
above.
III. Water, 2 quarts; isinglass, 5 ozs.; alum, 240 grains.
_Water-proof Glue._—Solution of glue by itself or mixed with pigments
is used in painting walls in distemper. A water-proof coat is obtained
as follows: Boil 1 part of powdered gall-nuts and 12 parts of water
until the mass is reduced to two-thirds of its bulk. Then strain
through a cloth and apply the solution to the dry coat of distemper
paint, the latter becoming thereby as solid and insoluble as oil-paint.
The tannin of the gall-nuts acting only upon soft glue, the solution
has to be applied so the lower layer of glue becomes thoroughly soaked
through.
To render _wrapping paper_ water-proof the following glue-solution may
be used: Dissolve 24 parts of alum and 4 parts of white soap in 32
parts of water in one pot, and in another 2 parts of gum arabic and 6
parts of glue in 32 parts of water, and mix the two solutions. Heat
the mixture, immerse the wrapping paper in it, and pass it through hot
rolls, or dry upon twine stretched in frames.
_Fabrics may be rendered water-proof_ with glue and tannin. The process
is based on the fact that by the action of tannin or bichromates,
compounds insoluble in water are formed. It is, however, of first
importance that both solutions—tannin and glue—should fully penetrate
the fabric. If the latter is dipped directly into strong solution of
glue and then of tannin, the glue will only become insoluble on the
outside, and that which has penetrated deeper into the fibre will be
unchanged, having been protected by the superficial insoluble layer.
Hence, the treatment is commenced with a very weak solution of glue,
prepared by leaving glue broken small in hundred times its weight of
water for twenty-four hours. By that time the glue will have swelled
up, and the whole is boiled, whilst being constantly stirred, so as
to get a perfectly clear solution in which the fabric is boiled for
10 to 15 minutes. This time is no more than necessary for complete
penetration. The fabric is then well wrung between two rollers placed
over the glue-bath so that excess of solution runs back into it. The
fabric is then hung up, and when nearly dry is passed through a tannin
solution. The latter may be made from tannin itself, or from a tannin
extract, or by boiling galls or oak bark in water. The tannin solution
can be used fairly strong, as only so much of it is taken up as
corresponds to the glue present, and it can be used over again as long
as it can supply the tannin required, and can then be reinforced with
more tannin as required.
It is not necessary for the fabric to stay long in the tannin, as it
reacts quickly with the glue. The tanned material is again hung up
to dry, and when quite dry is washed in plain water to remove any
excess of tannin. The whole process from the beginning is then twice
repeated. After this second repetition there is so thick a layer of
tannate of gelatine on the fabric that the dry cloth has acquired
considerable solidity and a smoothness which recalls that of leather.
The fabric is now passed through a stronger glue solution, using three
or even four parts of glue per hundred of water, but never exceeding
the latter limit. After the glue-bath the fabric goes through the
tannin bath, whereby it becomes quite thickly coated with tannate of
gelatine. By repeatedly treating with glue and tannin alternately,
this coating can be made as thick as desired, and finally masses are
obtained in which the texture of the fabric is entirely hidden, and
especially after the fabric has been calendered under heavy pressure
after water-proofing. The color acquired by goods thus water-proofed is
a more or less dark leather-brown.
Muratori and Landry treat the fabric with a solution made in three
separate operations:
1. Potash alum 100 lbs. dissolved in 10 gallons of boiling water.
2. In another vessel 100 lbs. of glue are soaked in cold water till the
glue has trebled in weight. The remaining water is poured off, and the
glue liquefied by the application of heat. When the glue is boiling, 5
lbs. of tannin and 2 lbs. of soda water glass are put in it.
3. The two solutions are boiled together, being stirred constantly.
When the mixture is complete, it is allowed to cool to a jelly. To
water-proof the goods some of the jelly is boiled with water (1 gallon
to 1 lb., or a little over) for three hours, adding water to compensate
for evaporation, so as to keep the volume of the solution constant,
as shown by tests of its specific gravity with a hydrometer. The bath
is then allowed to cool to 176° F., and the fabric is soaked in it
for half an hour and then stretched out horizontally for six hours
to drain. The fabric must be kept horizontal, so that the solution
remains uniformly distributed through it. The drainings are collected
to be used over again. The fabric is then dried in the open air or in a
drying room, still in the horizontal position. If a drying room is used
the temperature of it should not exceed 122° F.
Muzmann and Krakowitzer dissolve 10 lbs. of gelatine and 10 lbs. of
tallow soap in 30 gallons of boiling water, and mix the solution in
4 gallons of water in which 15 lbs. of alum have been dissolved. The
whole is boiled for half an hour, and then allowed to cool to 104°
F. At that temperature the fabric is thoroughly soaked in it, dried,
rinsed, again dried, and finally calendered. In this process the alum
partially decomposes the soap, forming either free fatty acid or an
acid alumina soap. The gelatine forms an insoluble compound with the
alum. The free fatty acid or acid soap is mostly carried down on the
fibre by the precipitate formed by the alum and the gelatine.
_Glue for Joints in Leather Driving Belts._—Soak equal parts of good
hide glue and isinglass in water for 10 hours, and then boil with pure
tannin till the product becomes sticky. The surfaces to be cemented
together should be roughened and the glue applied hot.
According to another method 2 lbs. of best glue are dissolved at a
moderate heat in 3 lbs. of water and about 3 drachms of carbolic acid
stirred into the hot solution. The mixture is poured into shallow iron
pans to congeal, when it is cut in pieces and dried in the air. For use
the glue is liquefied by adding a small quantity of vinegar and applied
with a brush to the leather. The joint is finally pressed between iron
plates at a temperature of about 77° F.
_Hectograph Mass._—Soak a good quality of glue for 24 hours in
sufficient cold water to cover it. Then take the swelled glue from
the water and melt it in an enameled pot over a moderate fire. When
perfectly liquid add the required quantity of glycerine (see formulas
below) and intimately mix both by continued stirring.
The vessel containing the mixture should for some time be kept hot, so
that the mass remains thinly fluid. The purpose of this is to allow
the air-bubbles formed by stirring to rise to the surface. If any scum
is formed on the surface, remove it carefully with a shallow spoon.
The composition is then ready to be poured into the vessel intended
for its reception, which may be made especially for the purpose, or a
shallow baking pan of tin may be used. When the pan is filled with the
composition place it perfectly level in a cool place free from dust and
allow to remain at least for several hours.
_Formulas for Hectograph Masses._—I. Gilder’s glue, 100 parts;
glycerine of 28° Bé., 500.
The glue is allowed to swell in water, as described above, then melted,
mixed with the glycerine, and evaporated to the required consistency.
II. Gilder’s glue, 100 parts; glycerine of 28° Bé., 400; water, 200.