skins, hides, etc., and from bones. The latter are submitted to the
action of dilute hydrochloric acid for several days, which attacks the
inorganic matters—carbonates, phosphates, etc., and leaves the ossein,
which is, so to say, an isomer of the skin substance. The skin, parings
of hide, etc., gathered from the shambles, butcher shops, etc., are
brought into the factory, and if not ready for immediate use are thrown
into quicklime, which preserves them for the time being. From the lime,
after washing, they pass into dilute acid, which removes the last
traces of lime, and are now ready for the treatment that is to furnish
the pure gelatin. The ossein from bones goes through the same stages
of treatment, into lime, washed and laid in dilute acid again. From
the acid bath the material goes into baths of water maintained at a
temperature not higher than from 175° to 195° F.
The gelatin manufacturer buys from the button-makers and manufacturers
of knife handles and bone articles generally, those parts of the bone
that they cannot use, some of which are pieces 8 inches long by a half
inch thick.
Bones gathered by the ragpickers furnish the strongest glue. The
parings of skin, hide, etc., are from those portions of bullock hides,
calf skins, etc., that cannot be made use of by the tanner, the heads,
legs, etc.
The gelatin made by Coignet for the Pharmacie Centrale de France is
made from skins procured from the tawers of Paris, who get it directly
from the abattoirs, which is as much as to say that the material is
guaranteed fresh and healthy, since these institutions are under rigid
inspection and surveillance of government inspectors and medical men.
There is a gelatin or glue, used exclusively for joiners, inside
carpenters, and ceiling makers (_plafonneurs_), called _rabbit
vermicelli_, and derived from rabbit skins. As the first treatment of
these skins is to saturate them with mercury bichloride, it is needless
to say the product is not employed in pharmacy. {370}
«To Clarify Solutions of Gelatin, Glues, etc.»—If 1 per cent of
ammonium fluoride be added to turbid solutions of gelatin or common
glue, or, in fact, of any gums, it quickly clarifies them. It causes a
deposition of ligneous matter, and also very materially increases the
adhesive power of such solutions.
«Air Bubbles in Gelatin.»—The presence of minute air bubbles in cakes
of commercial gelatin often imparts to them an unpleasant cloudy
appearance. These minute air bubbles are the result of the rapid,
continuous process of drying the sheets of gelatin by a counter-current
of hot air. Owing to the rapid drying a hard skin is formed on the
outside of the cake, leaving a central layer from which the moisture
escapes only with difficulty, and in which the air bubbles remain
behind. Since the best qualities of gelatin dry most rapidly, the
presence of these minute bubbles is, to a certain extent, an indication
of superiority, and they rarely occur in the poorer qualities of
gelatin. If dried slowly in the old way gelatin is liable to be damaged
by fermentation; in such cases large bubbles of gas are formed in the
sheets, and are a sign of bad quality.
«GEMS, ARTIFICIAL:»
See also Diamonds.
The raw materials for the production of artificial gems are the finest
silica and, as a rule, finely ground rock crystals; white sand and
quartz, which remain pure white even at a higher temperature, may also
be used.
Artificial borax is given the preference, since the native variety
frequently contains substances which color the glass. Lead carbonate
or red lead must be perfectly pure and not contain any protoxide,
since the latter gives the glass a dull, greenish hue. White lead and
red lead have to dissolve completely in dilute nitric acid or without
leaving a residue; the solution, neutralized as much as possible,
must not be reddened by prussiate of potash. In the former case tin
is present, in the latter copper. Arsenious acid and saltpeter must
be perfectly pure; they serve for the destruction of the organic
substances. The materials, without the coloring oxide, furnish the
starting quantity for the production of artificial gems; such glass
pastes are named “strass.”
The emerald, a precious stone of green color, is imitated by melting
1,000 parts of strass and 8 parts of chromic oxide. Artificial emeralds
are also obtained with cupric acid and ferric oxides, consisting of
43.84 parts of rock crystal; 21.92 parts of dry sodium carbonate; 7.2
parts of calcined and powdered borax; 7.2 parts of red lead; 3.65 parts
of saltpeter; 1.21 parts of red ferric oxide, and 0.6 parts of green
copper carbonate.
Agates are imitated by allowing fragments of variously colored pastes
to flow together, and stirring during the deliquation.
The amethyst is imitated by mixing 300 parts of a glass frit with 0.6
parts of gray manganese ore, or from 300 parts of frit containing 0.8
per cent of manganic oxide, 36.5 parts of saltpeter, 15 parts of borax,
and 15 parts of minium (red lead). A handsome amethyst is obtained by
melting together 1,000 parts of strass, 8 parts of manganese oxide, 5
parts of cobalt oxide, and 2 parts of gold purple.
Latterly, attempts have also been made to produce very hard glasses for
imitation stones from alumina and borax with the requisite coloring
agents.
Besides imitation stones there are also produced opaque glass pastes
bearing the name of the stones they resemble, e. g., aventurine,
azure-stone (lapis lazuli), chrysoprase, turquoise, obsidian, etc. For
these, especially pure materials, as belonging to the most important
ingredients of glassy bodies, are used, and certain quantities of red
lead and borax are also added.
GEM CEMENTS: See Adhesives, under Jewelers’ Cements.
GERMAN SILVER: See Alloys.
GERMAN SILVER SOLDERS: See Solders.
GILDING: See Paints, Plating, and Varnishes.
GILDING GLASS: See Glass.
GILDING, TO CLEAN: See Cleaning Preparations and Methods.
GILDING, RENOVATION OF: See Cleaning Compounds.
GILDING SUBSTITUTE: See Plating.
GILT, TEST FOR: See Gold.
GILT WORK, TO BURNISH: See Gold. {371}
GINGERADE: See Beverages.
GINGER ALE AND GINGER BEER: See Beverages.
GINGER CORDIAL: See Wines and Liquors.
GINGER EXTRACTS: See Essences and Extracts.
«Glass»
«Bent Glass.»—This was formerly used for show cases; its use in store
fronts is becoming more and more familiar, large plates being bent
for this purpose. It is much used in the construction of dwellings,
in windows, or rounded corners, and in towers; in coach fronts and in
rounded front china closets. Either plain glass or beveled glass may be
bent, and to any curve.
The number of molds required in a glass-bending establishment is large.
The bending is done in a kiln. Glass melts at 2,300° F.; the heat
employed in bending is 1,800° F. No pyrometer would stand long in that
heat, so the heat of the kiln is judged from the color of the flame
and other indications. Smaller pieces of glass are put into the molds
in the kilns with forks made for the purpose. The great molds used for
bending large sheets of glass are mounted on cars, that may be rolled
in and out of kilns. The glass is laid upon the top of the mold or
cavity, and is bent by its own weight. As it is softened by the heat
it sinks into the mold and so is bent. It may take an hour or two to
bend the glass, which is then left in the kiln from 24 to 36 hours to
anneal and cool. Glass of any kind or size is put into the kilns in
its finished state; the great heat to which it is subjected does not
disturb the polished surface. Despite every precaution more or less
glass is broken in bending. Bent glass costs about 50 per cent more
than the flat.
The use of bent glass is increasing, and there are 4 or 5 glass-bending
establishments in the United States, of which one is in the East.
«Colored Glass.»—R. Zsigmondy has made some interesting experiments
in coloring glass with metallic sulphides, such as molybdenite, and
sulphides of antimony, copper, bismuth, and nickel. Tests made with
batches of 20 to 40 pounds and with a heat not too great, give good
results as follows:
Sand, 65 parts; potash, 15 parts; soda, 5 parts; lime, 9 parts;
molybdenite, 3 parts; sulphide of sodium, 2 parts, gave a dark
reddish-brown glass. In thinner layers this glass appeared light
brownish yellow. Flashed with opal, it became a smutty black brown.
Sand, 50 parts; potash, 15 parts; soda, 5 parts; lime, 9 parts;
molybdenite, 1 part; sulphide of sodium, 2 parts, gave a yellow glass.
Sand, 10 parts; potash, 3.3 parts; soda, 0.27 parts; lime, 1.64 parts;
molybdenite, 0.03 parts, gave a reddish-yellow glass with a fine tinge
of red.
Sand, 100 parts; potash, 26 parts; soda, 108 parts; lime, 12 parts;
sulphide of copper, 1.7 parts; sulphide of sodium, 2.3 parts, gave a
dark-brown color, varying from sepia to sienna. In thick layers it was
no longer transparent, but still clear and unclouded. When heated this
glass became smutty black brown and clouded.
A fine copper red was obtained from sand, 10 parts; potash, 3 parts;
lime, 1.2 parts; soda, 0.25 parts; sulphide of copper, 7.5 parts;
sulphide of sodium, 10.5 parts; borax, 9.5 parts.
Attempts to color with sulphides of antimony and bismuth failed. But
the addition of 7 per cent of sulphide of nickel to an ordinary batch
gave a glass of fine amethyst color.
«Coloring Electric-Light Bulbs and Globes.»—Two substances suggest
themselves as excellent vehicles of color, and both water soluble—water
glass (potassium or sodium silicate) and gelatin. For tinting,
water-soluble aniline colors should be tried. The thickness of the
solution must be a matter of experimentation. Prior to dipping the
globes they should be made as free as possible from all grease, dirt,
etc. The gelatin solution should not be so thick that any appreciable
layer of it will form on the surface of the glass, and to prevent
cracking, some non-drying material should be added to it, say glycerine.
«Rose-Tint Glass.»—Selenium is now used for coloring glass. Rose-tinted
glass is made by adding selenium directly to the ingredients in the
melting pot. By mixing first with cadmium sulphide, orange red is
produced. This process is stated not to require the reheating of the
glass and its immersion in the coloring mixture, as in the ordinary
process of making red glass.
«CUTTING, DRILLING, GRINDING, AND SHAPING GLASS:»
«To Cut Glass.»—I.—Glass may be cut without a diamond. Dip a piece of
{372} common string in alcohol and squeeze it reasonably dry. Then tie
the string tightly around the glass on the line of cutting. Touch a
match to the string and let it burn off. The heat of the burning string
will weaken the glass in this particular place. While it is hot plunge
the glass under water, letting the arm go well under to the elbow, so
there will be no vibration when the glass is struck. With the free hand
strike the glass outside the line of cutting, giving a quick, sharp
stroke with a stick of wood, a long-bladed knife, or the like, and the
cut will be as clean and straight as if made by a regular glass cutter.
The same principle may be employed to cut bottles into vases, and to
form all sorts of pretty things, such as jewelry boxes, picture panes,
trays, small tablets, windows for a doll house, etc.
II.—Scratch the glass around the shape you desire with the corner of a
file or graver; then, having bent a piece of wire into the same shape,
heat it red hot and lay it upon the scratch and sink the glass into
cold water just deep enough for the water to come almost on a level
with its upper surface. It will rarely fail to break perfectly true.
«To Cut Glass Under Water.»—It is possible to cut a sheet of glass
roughly to any desired shape with an ordinary pair of scissors, if the
operation be performed under water. Of course, a smooth edge cannot be
obtained by such means, but it will be found satisfactory.
«Drilling, Shaping, and Filing Glass.»—Take any good piece of steel
wire, file to the shape of a drill, and then hold it in a flame till
it is at a dull red heat; then quench in metallic mercury. A piece of
good steel, thus treated, will bore through glass almost as easily as
through soft brass. In use, lubricate with oil of turpentine in which
camphor has been dissolved. When the point of the drill has touched the
other side put the glass in water, and proceed with the drilling very
slowly. If not possible to do this, reverse the work—turn the glass
over and drill, very carefully, from the opposite side. By proceeding
with care you can easily drill three holes through glass 3/16 inch
thick 1/4 of an inch apart. In making the drill be careful not to
make the point and the cutting edges too acute. The drill cuts more
slowly, but more safely, when the point and cutting edges are at a low
angle.
«To Make Holes in Thin Glass.»—To produce holes in panes of thin or
weak glass, provide the places to be perforated with a ring of moist
loam, whose center leaves free a portion of glass exactly the size of
the desired hole. Pour molten lead into the ring, and the glass and
lead will fall through at once. This process is based upon the rapid
heating of the glass.
«To Grind Glass.»—For the grinding of glass, iron, or steel laps and
fine sand are first used; after that, the sand is replaced by emery.
Then the polishing is started with pure lead or pure tin laps, and
finished with willow wood laps. The polishing powder is tin putty, but
peroxide of iron or dioxide of tin is a good polishing medium.
Pohl asserts that if glass is polished with crocus (Paris red) it
appears of a dark or a yellowish-brown tint. He contends that the
crocus enters the pores of the glass, and, to prevent this, he uses
zinc white with the most satisfactory results.
«A Home-Made Outfit for Grinding Glass.»—Provide two pieces of cork,
one concave and one convex (which may be cut to shape after fitting
to the lathe). Take a copper cent or other suitable article and
soft-solder a screw to fit the lathe, and then wax it to the cork; get
a cheap emery wheel, such as is used on sewing machines. Polish the
edge on the zinc collar of the emery wheel (or use a piece of zinc).
The other cork should be waxed to a penny and centered. Spectacle
lenses may be cut on the same emery wheel if the wheel is attached to
the lathe so as to revolve. Another method is to take a common piece of
window glass (green glass is the best) and make a grindstone of that,
using the flat surface for grinding. Cement it on a large chuck, the
glass being from 2 to 2 1/2 inches in diameter.
«To Drill Optical Glass.»—A graver sharpened to a long point is twisted
between the fingers, and pressed against the glass, the point being
moistened from time to time with turpentine. When the hole is finished
half way, the drilling should be commenced from the other side. The
starting should be begun with care, as otherwise the graver is likely
to slide out and scratch the lens. It is advisable to mark the point
of drilling with a diamond, and not to apply too great a pressure when
twisting the graver.
«Lubricants for Glass Drilling.»—I.—Put garlic, chopped in small
pieces, into spirit of turpentine and agitate the {373} mixture from
time to time. Filter at the end of a fortnight, and when you desire to
pierce the glass dip your bit or drill into this liquid, taking care to
moisten it constantly to prevent the drill, etc., from becoming heated.
II.—Place a little alum in acetic acid, dip your drill into this and
put a drop of it on the spot where the glass is to be pierced.
«GILDING GLASS.»
When it is desired to gild glass for decorative purposes use a solution
of gelatin in hot water, to which an equal quantity of alcohol has been
added. The glass to be gilded is covered with this solution and the
gold leaf put on while wet. A sheet of soft cotton must be pressed and
smoothed over the leaf until the gelatin below is evenly distributed.
This prevents spots in gilding. Careful apportionment of the gelatin
is necessary. If too much be used, the gold may become spotted; if too
little, the binding may be too weak to allow the gold to be polished.
The glass should be cleaned thoroughly before gilding. After the gold
leaf is put on the whole is allowed to dry for 10 or 20 minutes, when
the luster of the gold can be raised by a cautious rubbing with cotton.
Then another layer of gelatin is spread on with one stroke of a soft
brush, and, if especially good work be required, a second layer of gold
is put on and covered as before. In this case, however, the gelatin is
used hot. After the gilding has become perfectly dry the letters or
ornamentation are drawn and the surplus gold around the edges is taken
off. The gilding does not become thoroughly fixed until after several
months, and until then rough handling, washing, etc., should be avoided.
The best backing for glass gilding is asphaltum, with a little
lampblack, this to be mixed up with elastic varnish; outside finishing
varnish is the best, as the addition of this material gives durability.
«GLASS MANUFACTURING:»
See also Ceramics.
The blue tint of the common poison bottle is got by the addition of
black oxide of cobalt to the molten glass; the green tint of the
actinic glass bottle is obtained in the same way by the addition of
potassium bichromate, which is reduced to the basylous condition, and
the amber tint is produced by the addition of impure manganese dioxide,
a superior tint being produced by suphur in one form or another. The
formulas for various kinds of bottle glass, which indicate the general
composition of almost all glasses, are:
White Glass for Ordinary Molded Bottles.—
Sand 64 parts by weight
Lime 6 parts by weight
Carbonate of sodium 23 parts by weight
Nitrate of sodium 5 parts by weight
White Flint Glass Containing Lead.—
Sand 63 parts by weight
Lime 5 parts by weight
Carbonate of sodium 21 parts by weight
Nitrate of sodium 3 parts by weight
Red lead 8 parts by weight
Ordinary Green Glass for Dispensing Bottles.—
Sand 63 parts by weight
Carbonate of sodium 26 parts by weight
Lime 11 parts by weight
Amixture for producing a good green flint glass is much the same as that
for the ordinary white flint glass, except that the lime, instead of
being the purest, is ordinary slaked lime, and the sodium nitrate is
omitted. Sand, lime, and sodium carbonate are the ordinary bases of
glass, while the sodium nitrate is the decolorizing agent.
Glass Refractory to Heat.—Fine sand, 70 parts; potash, 30 parts;
kaolin, 25 parts.
Transparent Ground Glass.—Take hold of the glass by one corner with an
ordinary pair of fire tongs. Hold it in front of a clear fire, and heat
to about 98° F., or just hot enough to be held comfortably in the hand.
Then hold the glass horizontally, ground side uppermost, and pour in
the center a little photographer’s dry-plate negative varnish. Tilt the
glass so that the varnish spreads over it evenly, then drain back the
surplus varnish into the bottle from one corner of the glass. Hold the
glass in front of the fire again for a few minutes and the varnish will
crystallize on its surface, making it transparent. The glass should not
be made too hot before the varnish is put on, or the varnish will not
run evenly. This method answers very well for self-made magic-lantern
slides. Ground glass may be made temporarily transparent by wiping with
a sponge dipped in paraffine or glycerine.
«WATER-TIGHT GLASS:»
«Water-Tight Glass Roofs.»—Glass roofs, the skeletons of which are
constructed {374} of iron, are extremely difficult to keep water-tight,
as the iron expands and contracts with atmospheric changes. To meet
this evil, it is necessary to use an elastic putty, which follows the
variations of the iron. A good formula is: Two parts rosin and one part
tallow, melted together and stirred together thoroughly with a little
minium. This putty is applied hot upon strips of linen or cotton cloth,
on top and below, and these are pasted while the putty is still warm,
with one edge on the iron ribs and the other, about one-fourth inch
broad, over the glass.
«Tightening Agent for Acid Receptacles.»—Cracked vessels of glass or
porcelain, for use in keeping acids, can be made tight by applying
a cement prepared in the following manner: Take finely sifted sand,
some asbestos with short fiber, a little magnesia and add enough
concentrated water glass to obtain a readily kneadable mass. The acid
renders the putty firm and waterproof.
«PENCILS FOR MARKING GLASS:»
See also Etching and Frosted Glass.
Crayons for Writing on Glass.—I.—The following is a good formula:
Spermaceti 4 parts
Tallow 3 parts
Wax 2 parts
Red lead 6 parts
Potassium carbonate 1 part
Melt the spermaceti, tallow, and wax together over a slow fire, and
when melted stir in, a little at a time, the potassium carbonate
and red lead, previously well mixed. Continue the heat for 20 or 30
minutes, stirring constantly. Withdraw from the source of heat, and
let cool down somewhat, under constant stirring, at the temperature
of about 180° F.; before the mixture commences to set, pour off into
molds and let cool. The latter may be made of bits of glass tubing of
convenient diameter and length. After the mixture cools, drive the
crayons out by means of a rod that closely fits the diameter of the
tubes.
II.—Take sulphate of copper, 1 part, and whiting, 1 part. Reduce these
to a fine powder and mix with water; next roll this paste into the
shape of crayons and let dry. When it is desired to write on the glass
use one of these crayons and wipe the traced designs. To make them
reappear breathe on the glass.
III.—Melt together, spermaceti, 3 parts; talc, 3 parts, and wax, 2
parts. When melted stir in 6 parts of minium and 1 part of caustic
potash. Continue heating for 30 minutes, then cast in suitable molds.
When formed and ready to be put away dust them with talc powder, or
roll each pencil in paraffine powder.
«PREVENTION OF FOGGING, DIMMING, AND CLOUDING.»
I.—Place a few flat glass or porcelain dishes with calcium chloride in
each window. This substance eagerly absorbs all moisture from the air.
The contents of the dishes have to be renewed every 2 or 3 days, and
the moist calcium chloride rigorously dried, whereupon it may be used
over again.
II.—Apply to the inside face of the glass a thin layer of glycerine,
which does not permit the vapor to deposit in fine drops and thus
obstruct the light. Double glass may also be used. In this way the heat
of the inside is not in direct contact with the cold outside.
III.—By means of the finger slightly moistened, apply a film of soap of
any brand or kind to the mirror; then rub this off with a clean, dry
cloth; the mirror will be as bright and clear as ever; breathing on it
will not affect its clearness.
IV.—Window glass becomes dull during storage by reason of the presence
of much alkali. This can be avoided by taking sand, 160 parts; calcined
sodium sulphate, 75; powdered marble, 50; and coke, 4 to 5 parts. About
3 parts of the sodium sulphate may be replaced by an equal quantity of
potash.
«FROSTED GLASS.»
I.—A frosted appearance may be given to glass by covering it with a
mixture of
Magnesium sulphate 6 ounces
Dextrin 2 ounces
Water 20 ounces
When this solution dries, the magnesium sulphate crystallizes in fine
needles.
II.—Another formula directs a strong solution of sodium or magnesium
sulphate, applied warm, and afterwards coated with a thin solution of
acacia.
III.—A more permanent “frost” may be put on the glass by painting with
white lead and oil, either smooth or in stipple effect. The use of lead
acetate with oil gives a more pleasing effect, perhaps, than the plain
white lead.
IV.—If still greater permanency is desired, the glass may be ground by
rubbing with some gritty substance. {375}
V.—For a temporary frosting, dip a piece of flat marble into glass
cutter’s sharp sand, moistened with water; rub over the glass, dipping
frequently in sand and water. If the frosting is required very fine,
finish off with emery and water. Mix together a strong, hot solution
of Epsom salt and a clear solution of gum arabic; apply warm. Or use a
strong solution of sodium sulphate, warm, and when cool, wash with gum
water. Or daub the glass with a lump of glazier’s putty, carefully and
uniformly, until the surface is equally covered. This is an excellent
imitation of ground glass, and is not disturbed by rain or damp.
VI.—This imitates ground glass:
Sandarac 2 1/2 ounces
Mastic 1/2 ounce
Ether 24 ounces
Benzine 16 to 18 ounces