_a._ By analysis:--
1. (M. Berthier.) Silica, 71·7%; potassa, 12·7%; soda, 2·3%; lime, 10·3%;
alumina, ·4%; oxides of iron and manganese (and loss), 2·6%. Very white,
hard, and beautiful table glass.
2. (Dumas.) Silica, 70%; potassa, 20%; lime, 4%; alumina, 5%; oxide of
iron, ·6%; peroxide of manganese, ·4%. A beautiful white wineglass.
_b._ Materials used:--
1. Finest sand, 50%; purified potashes, 25%; chalk, 10%; nitre, 2%;
crystal cullet, 27%; manganese, a little (say 1/16%). Used in England
recently for table glass.
2. Quartz (hyalin, in powder), 63%; purified potashes, 26%; slaked lime
(carefully sifted), 11%; manganese, a little; crystal cullet, at will.
Used in Bohemia.
3. (M. Perdonnet.) Powdered quartz, 44%; carbonate of potassa, 33%;
quicklime (in fine powder), 22%; nitre, 1%; and a very small quantity of
arsenious acid and peroxide of manganese. Said to be the formula used at
Neuwelt for the glass _a_, 1 (_above_).
_Qual., &c._ These are denoted by its hardness, transparency, homogeneity,
strength, and power of resisting the action of water, air, light, and the
stronger acids and alkalies. The power of glass to resist the action of
menstrua is readily tried by exposing it to boiling oil of vitriol, and
hot but dilute solution of caustic potassa. Neither of these tests should
cause the glass to lose its transparency or to become dim.
_Swallowed glass._ Glass and enamel, both in fragments and in powder, have
occasionally been swallowed, with different results. These bodies are
insoluble in the fluids of the body, and, consequently, any injurious
action they may exert upon the system whilst they are retained in it must
entirely depend upon mechanical attrition or irritation. As treatment, we
must administer an emetic, and assist its action by thick mucilaginous
liquids, and afterwards have recourse to antiphlogistics, if necessary.
_Anal._--_a._ A portion of the sample for examination is heated to dull
redness, and then suddenly thrown, whilst still hot, into a vessel of cold
water. It is next dried, and reduced to fine powder in an agate or
hardened-steel mortar.
_b._ 100 gr. of the prepared powder is thoroughly mixed with 200 gr. of
pure potassic hydrate, and the whole is exposed to heat in a silver or
platinum crucible or capsule until perfect fusion takes place; when cold,
the crucible and its contents are boiled in about half a pint of distilled
water; nitric acid is added to the resulting solution, in excess, and the
mixture, together with any sediment, is evaporated to dryness, after which
the heat is gradually increased to 400° or 500° Fahr.; the dry residuum is
next reduced to powder, and digested in water acidulated with nitric acid,
until exhausted of soluble matter; the insoluble portion is then carefully
dried, gently ignited and weighed. The weight in grains represents the
per-centage of silica in the sample examined.
_c._ The mixed liquid and washings of _b_ is next acidulated with nitric
acid, and treated to a stream of sulphuretted hydrogen, which, if it
produces a precipitate, is continued for some time; the precipitate is
collected on a very small filter, washed, and dried; the filter with the
precipitate next placed in a beaker glass, and strong fuming nitric acid
is cautiously added, drop by drop, until complete solution takes place;
after boiling the solution for a few minutes, diluting with distilled
water, and allowing it to cool, it is precipitated with sulphuric acid, in
excess; this precipitate (sulphate of lead) is washed, dried, slightly
ignited in a porcelain crucible, and weighed. The weight in grains,
multiplied by ·7369, gives the per-centage of oxide of lead or litharge.
_d._ The filtered liquid from _c_ is evaporated to dryness, and
redissolved in water acidulated with hydrochloric acid, and treated with a
solution of ammonium chloride, and afterwards with ammonia, in excess; the
precipitate (alumina and oxide of iron) is collected, washed, and boiled
in a solution of potassium hydrate; the undissolved portion is collected
on a filter, washed with boiling water, ignited, and weighed. This gives
the per-centage of peroxide of iron.
_e._ The liquid filtered from the oxide of iron holds the alumina (if any)
in solution; a solution of carbonate of ammonium is dropped in; the
resulting precipitate is washed, dried, ignited, and weighed. This gives
the per-centage of alumina.
_f._ The filtrate from the alumina and oxide of iron (see _d_), after
being evaporated to dryness, is redissolved in a large quantity of
distilled water, and is treated with a solution of oxalic acid (a solution
of oxalate of ammonium is preferable when no baryta is present); the
precipitate is washed, dried, gently ignited, and weighed. The weight of
the resulting carbonate of calcium, in grains, multiplied by ·56292, gives
the per-centage of lime required.
_g._ The filtrate from _f_ is now mixed with carbonate of potassium, in
considerable excess, and boiled for a long time; the resulting precipitate
(if any) is then collected on a filter, slightly washed with hot water,
dried, and exposed to a full red heat for some time (say 2 hours); the
residuum of the calcination is then weighed. This furnishes the
per-centage value of the sample in magnesia.
_h._ The filtrate from _f_ is treated with dilute sulphuric acid or the
solution of a sulphate, as long as a precipitate falls; the precipitate
(sulphate of barytum,) is washed, dried, gently ignited, and weighed. The
weight, in grains, multiplied by ·6589, gives the per-centage of baryta in
the sample.
The above may be varied by gently concentrating the liquid filtered from
the precipitate of alumina and oxide of iron (see _d_), and precipitating
it with dilute sulphuric acid; the mixed precipitate is exhausted by
digestion in water holding chloride of ammonium in solution; the
undissolved residuum (sulphate of barytum,) is washed, dried, and
otherwise treated as before; whilst the solution with the washings is
treated with a solution of carbonate of ammonium; the precipitate is
carbonate of calcium, which is to be washed, &c., as directed under _f_.
The liquor, &c., filtered from the lime, is lastly tested for magnesia.
(See _g_.)
_i._ A second 100 gr. of the powdered glass (see _a_) is mixed with 200
gr. of fluor spar, also in powder; the compound is placed in a platinum or
leaden capsule, 500 gr. of strong sulphuric acid are added, and the whole
cautiously stirred together with a silver stirrer or spoon, care being
taken to avoid inhaling the fumes; the heat of a spirit lamp is next
applied, and at first is kept at about 212° Fahr., but towards the
conclusion of the process is raised to 300° Fahr., or even higher, and is
continued for at least 2 hours, or until fumes entirely cease to be
evolved; 5 or 6 fl. oz. of distilled water are next poured on the
residuary mass, and, after thorough agitation, the whole is thrown on a
filter, more water being at last poured on to wash out any remains of
soluble matter; to the filtrate, carbonate of ammonium is added in excess,
and after a time the earthy salts are removed by filtration; the filtered
liquor is now evaporated to dryness, and ignited to dull redness for 2 or
3 minutes; the residuum (sulphate of potassium or sodium, or of both),
after being weighed (the weight being carefully noted down), is
redissolved in distilled water; a solution of chloride of barium is then
added as long as it disturbs the liquor, and after a time the whole is
again filtered; the filtrate is concentrated by evaporation, and solution
of bichloride of platinum added in excess; the whole is now gently
evaporated to dryness, mixed with alcohol, collected on a filter,
carefully washed with weak alcohol, dried at a temperature under 212°
Fahr., and weighed. The weight, in grains, multiplied by ·1940, gives the
per-centage of potassa sought.
_k._ The weight of sulphate of potassium in the ignited residuum in _i_ is
calculated from that of the potassium last found (47 parts of the one
being equal to 87 parts of the other), and this weight is deducted from
the gross weight of the ignited sulphates; the remainder represents the
quantity of sulphate of sodium present. The weight of the latter, in
grains, multiplied by ·4367, gives the per-centage of pure soda required.
_Concluding Remarks._ One of the chief points to which the skilful glass
manufacturer directs his attention, is the quality of the materials. Great
care is exercised in the selection of the sand for all the finer varieties
of glass. The usual practice is to test it before using it, by exposing it
to a very high temperature. The purest sand is that which is the whitest
and freest from iron, and which, consequently, suffers the least
alteration by this treatment. The alkalies (potash, soda) employed are
purified by solution and crystallisation. The red lead and litharge must
be pure and absolutely free from oxide of copper (a common contamination),
which gives a green tint to the glass. The former, which is the most
costly, is preferable to the finest crystal. Care must also be taken that
the lime, clay, &c., are respectively of proper purity; and that the
'cullet,' or broken glass, which is almost always remelted with the other
materials, is of proper quality, and of the same kind as that to which it
is added. Potassa produces a better glass than soda, although the latter
is now very generally employed, from its lower price. It is, however,
quite inadmissible as an ingredient in the manufacture of the better class
of crystal and plate glass, as, however pure it may be, it imparts to the
product a slight greenish tinge more or less destructive of its beauty.
When sulphate of soda (Glauber salt) is used as a source of soda, it is
gently calcined to dissipate its water of crystallisation, and requires
the addition of about 8% of charcoal to effect its reduction in the
melting-pot. Common salt is also employed as a source of soda in the same
manner. Sometimes native sulphide of lead (galena) is used to decompose
the sulphate of soda, and in lieu of part of the oxide of lead; in which
case about 5 parts of the sulphuret are taken for every 9 parts of the
calcined sulphate.
To anticipate the results of his processes, and to carry out with
certainty his various intentions, the glass manufacturer, perhaps more
than any other person, requires the aid of science and experience. All his
most essential operations depend on chemical principles. The products of
his furnaces are not formed by the mere mechanical admixture of their
several ingredients whilst in the state of fusion, but result from the
play of delicate affinities which only act under certain conditions, and
when the materials are presented to each other in uniform and definite
proportions. Chemically speaking, the glasses are mixed super-silicates of
the respective bases which enter into their composition (potassium,
calcium, lead, &c.), and, like all other compounds which are formed by
elective attraction, obey the common laws of combination, as developed by
Dalton, and now so successfully applied in almost every department of
industrial art. It has been shown by the most careful analysis, that in
all the more valuable and beautiful commercial glasses the relative
proportions of the materials are conformable to these laws, and that
several of them are true atomic compounds, as perfect in this respect as
the crystalline bodies commonly denominated salts. In some of the harder
glasses of Bohemia the number of atoms or equivalents of silica are to
each of the bases with which it is united, nearly as 5 to 1; whilst in a
softer glass of German manufacture the proportions of the two are found to
be as 4 to 1. The celebrated plate glass of St. Gobain is an atomic
compound formed of 1 equivalent of trisilicate of soda united to 1
equivalent of trisilicate of lime, with a small per-centage of alumina in
combination with silicic acid, also in atomic proportion. Glasses in which
the ingredients bear no atomic ratio to each other are never homogeneous,
but always more or less striated and of unequal colour and refractive
power. The absence of atomic proportion between the substances entering
into its composition appears to be the only reason why the best English
plate and mirror glass is so greatly inferior to that of France and
Germany, that comparison of the two becomes absurd. The only variety of
glass in the production of which the English manufacturer excels is flint
glass or crystal, and here he certainly surpasses all his numerous
competitors. The subject is doubtless involved in difficulty, owing to the
precise temperature necessary to effect the perfect combination of the
bases with the silicic acid, varying with the character of the compound,
and not being satisfactorily settled by observation or experience. The
modifying influence of temperature is shown by the fact that the lower the
heat employed in the process, the smaller the quantity of silica which
enters into the composition of the resulting glass; whilst at higher
temperatures a part of the base is dissipated in fumes, until such
proportions of base and acid result as are required to produce a permanent
atomic compound corresponding to the temperature employed. If the heat is
excessive or improperly continued, the loss of base produces an opposite
effect, and an opaque, semi-vitrified mass is formed, resembling
'Reaumur's porcelain.' The quality of the resulting glass depends on this
change being more or less complete. If the furnace yields the right
temperature, and the duration of the exposure to its action is neither too
short nor too prolonged, nature makes up for the unskilful conduct of the
operative, and removes the stumbling blocks which his ignorance had placed
in the way of his own attempts at excellence. The proceedings and their
results are accidental; but being once obtained, the first are repeated
without further trouble or inquiry. This accounts for the same mixture of
materials yielding products of different qualities at different times, and
in different works, which the operative contents himself with referring to
the 'going of the furnace.' The common plan in this country is to regulate
the proportions and firing by experience only, rather than by theory and
practice combined. Now, although the chemist has much yet to learn on the
precise constitution of the glasses, and although theory may not be able
to ensure unvarying success, it is nevertheless certain that, in all
cases, it can afford much valuable assistance in that direction. Indeed,
it has been asserted by one of the leading Continental chemists, that
ingredients that will yield the proper equivalent proportions in the
melting pot cannot produce a bad glass, if exposed to such a temperature
as to permit of perfect combination taking place.
It is found that those glasses which contain a predominance of alkali are
acted on by water, and when this is in great excess they are perfectly
soluble in that fluid. Ordinary flint glass is affected by long coction in
water, whilst crown glass, which contains less alkali, is unaltered by
that trial. Glass which contains any considerable quantity of lead is
acted on by sulphuretted hydrogen. This is the cause of the surface of
flint glass, under certain circumstances, becoming opaque and iridescent.
Glasses made of silica and alkali alone are incapable of permanently
resisting the action of water. The addition of lime or oxide of lead
appears to be necessary to give them this quality. Glasses that have a
slight greenish or bluish tint may be often whitened, or rendered
colourless, by exposure to light and air. This arises from the
peroxidation of the iron, to whose protoxide they owe their tint. Other
glasses become purpled by exposure, owing to the peroxidation of the
manganese.
Different colours are communicated to glass by the addition of metallic
oxides. Thus, oxide of manganese gives an amethyst; oxide of cobalt, a
blue; oxide of iron, a brown; black oxide of copper, a green; oxide of
gold, a purple; suboxide of copper, a ruby-red; oxide of tin, a white;
oxide of silver, a yellow, &c. These substances are either added to the
melted contents of the glass-pot, as in preparing artificial gems, &c., or
they are applied in a thin layer to the surface of the object, which is
then heated until fusion of the coloured compound occurs, as in enamelling
and painting on glass.
Glass is FORMED or FASHIONED into articles by the processes of blowing,
casting, drawing, rolling, or spreading. In the process of BLOWING GLASS
the workman begins by collecting a proper quantity of glass in a soft,
pasty state, at the end of his blow-pipe (an iron tube, five or six feet
in length, terminated by a mouth-piece of wood), which he then commences
blowing through, by which the lump is expanded into a kind of flask,
susceptible of having its form modified by the position in which it is
held, and the velocity of rotation continually given to the iron tube. If
an open-mouthed vessel is to be made, an iron rod, called a 'pontil' or
'puntil,' is dipped into the glass-pot and applied to the bottom of the
flask, to which it thus serves as a handle, the blow-pipe being removed by
the application of a cold iron to the neck. The vessel is now re-heated,
and the aperture enlarged, and the vessel otherwise altered in figure by
the aid of a few simple tools until completed. It is then detached, and
carried to the 'annealing oven,' where it undergoes slow and gradual
cooling during many hours. In this way bottles, flasks, carboys, and an
almost infinite variety of other articles, are formed. The large circular
tables of CROWN-GLASS are made by a joint process of BLOWING and
SPREADING. The globular flask at first produced, transferred from the
blow-pipe to the 'pontil,' is suddenly made to assume the form of a flat
disc by the centrifugal force of the rapid rotatory movement given to the
rod. SPREAD or BROAD GLASS is formed into sheets in a nearly similar
manner. PLATE-GLASS is cast upon a flat metal table, and, after very
careful annealing, is ground and polished by suitable machinery. TUBES are
made by rapidly drawing out a hollow cylinder; and from these a great
variety of useful small apparatus are constructed with the help of a lamp
and blowpipe, or, still better, the bellows-table of the barometer-maker.
GLASS BEADS are made from small tubes chopped into pieces of suitable
lengths, which are stirred first in a mixture of sand and wood-ashes, in
the cold, and afterwards in an iron pan over the fire until they assume a
rounded form. SMALL TUBES are bent in the flame of a spirit lamp or
gas-jet, and cut by a file, a scratch being made, and the two portions
pulled or broken asunder in a way easily learned by a few trials. LARGE
TUBES require the heat of a powerful blowpipe and lamp, or that of a
furnace.
The following hints respecting the MANAGEMENT OF GLASS may prove useful to
the inexperienced:--
ANNEALING. The process of annealing glass has been briefly referred to
before. The extreme brittleness of imperfectly annealed wrought glass may
generally be remedied on the small scale by immersing the articles in a
bath of oil, or a concentrated solution of chloride of calcium, or common
salt, and heating the whole gradually and cautiously to the boiling-point,
and letting it again cool--the slower the better. By this treatment the
glass will be enabled to bear any alterations of temperature between the
two extremes to which it has been exposed.
BLOWING. By the ingenious art of GLASS-BLOWING and GLASS-DRAWING, as
practised on the small scale, with a blowpipe lamp furnace, a variety of
articles of ornament and utility may be made, their number being limited
only by the ingenuity of the artist. The details of the various operations
are, however, too lengthy to describe here.
CLEANING. 1. Windows, looking-glasses, &c., may be quickly cleaned as
follows:--Dip a slightly moistened rag or flannel into whiting, fuller's
earth, wood-ashes, or rotten-stone, in impalpable powder, with which smear
the glass, and wipe it off with a dry, soft cloth. This does well when the
surface is very dirty. In other cases, a little thumb blue, whiting, or
chalk, in fine powder, tied up in muslin, may be dusted on the glass,
which should then be cleaned off with chamois leather. This gives a fine
polish.
2. The vessel to be cleansed, is filled, or, if large, rinsed, with a
moderately dilute solution of permanganate of potash, contact being
prolonged till a film of hydrated manganic oxide has been deposited; the
solution is then poured away, and the glass vessel rinsed with some strong
hydrochloric acid.
CUTTING. Glass may be easily cut with a common well-hardened steel file,
provided it be moistened with oil of turpentine, or plunged under water.
It may be also perforated with a common steel brad-awl in the same way.
GLASS VESSELS, as bottles and tubes, may be readily cut or shortened by
placing a heated iron ring over the spot, or a piece of loose string or
cotton dipped in oil of turpentine and set on fire, and immediately on the
withdrawal of either applying cold water to the part. Glass vessels or
tubes thus treated will generally crack round, and may be readily divided
into two parts. In this manner a common Florence oil-flask may be
converted into an evaporating dish and a funnel. By a little practice a
crack may be led in almost any direction, or a new one made, by the point
of a red-hot poker or a spring coal (an ignited crayon of prepared
charcoal). The parts may then be separated by a little force or a smart
rap, and the divided edges smoothed by the flame of a blowpipe, or by
grinding them with powdered emery and water on a flat stone. In this way
many broken articles in glass may be converted into others scarcely less
useful.
ETCHING ON GLASS has been already noticed under the head of Etching.
GILDING OF GLASS. Gold chloride is dissolved in boiling water; the
solution is filtered, and the filtrate so far diluted, that 200 cubic
centimètres contain 0·0648 gram of the metal, and it is then made alkaline
with soda. The reducing agent is alcohol saturated with marsh gas; this is
diluted with its own volume of water. 25 cubic centimetres of this
solution are mixed with the alkaline gold chloride solution, and this
mixture is poured between the perfectly well-cleaned plate to be gilded,
and another sheet of glass placed at a distance of 3 mm. under the first.
After two to three hours' rest the gilding is effected. The plate is
removed and washed. ('Dingler's Journal.')
GRINDING. This, on the large scale, like glass-cutting, forms a distinct
occupation. On the small scale, glass may be roughed or ground by friction
with powdered emery and water and a flat rubber of wood; care being taken
that the article, if a plate, is laid on a perfectly flat surface, or, if
hollow, is supported by a core of cement or plaster. The frosted
appearance of ground glass is given to the panes of windows by gently
dabbing the glass over with a piece of glazier's putty, stuck on the ends
of the fingers. When applied with a light and even touch, the resemblance
is considerable. Another method is to dab the glass over with thin white
paint, or flour paste, by means of a brush, but the effect is much
inferior to the above.
GLASS, PACKING. This subject will be considered under the general head of
PACKING.
WRITING ON GLASS may be performed by a piece of French chalk or crayons
prepared for the purpose; or even with a common pen held nearly
perpendicular. Indian ink, or, when the article will be exposed to damp,
shell-lac ink or varnish, thickened with a little Vermillion, or
lampblack, is best adapted to this purpose. Common ink is not sufficiently
opaque.
GLASS, TO PREVENT THE CRACKING OF, BY BOILING WATER. When new, all glass
and earthenware should be placed in cold water in a saucepan, and after
some hours the saucepan containing the vessel or vessels, should be placed
over the fire, until the water reaches the boiling point.
=Glass.= This term was applied by the older chemists to various substances
to which a vitreous appearance has been given by heat. Thus we have 'GLASS
OF ANTIMONY,' 'GLASS OF BORAX,' &c. It is now obsolete.
=Glass, Iridescent.= The inventor of the process by which this beautiful
variety of glass is made is M Clémandot.
The 'Chemical News' states that the principle observed in its manufacture
consists in submitting the glass articles to the action of dilute
hydrochloric, sulphuric, or other acid, under a pressure of from two to
six atmospheres. M Clémandot claims to be able to imitate the nacreous
films which are seen on ancient glass which has been exposed to combined
atmospheric influences for thousands of years.
=Glass, Pow'dered.= _Syn._ VITRUM PULVERISATUM, L. _Prep._ Heat the glass
red hot, throw it into cold water, dry, and powder it. Used to filter
acids, and glued upon paper as a polishing powder; also to wear down corns
upon the feet, after the feet have been well soaked, and dried.
=Glass, Sol'uble.= _Syn._ WATER GLASS; VITRUM SOLUBILE, L. An impure
alkaline silicate. _Prep._ Silica, 1 part; carbonate of potassium or of
sodium, 2 parts; fused together.
Carbonate of sodium (dry), 54 parts; carbonate of potassium (dry), 70
parts; silica, 192 parts; as last. Soluble in boiling water, yielding a
fine, transparent, semi-elastic varnish.
Carbonate of potassium (dry), 10 parts; powdered quartz (or sand free from
iron and alumina), 15 parts; charcoal 1 part; fused together. Soluble in 5
or 6 times its weight of boiling water; and the filtered solution,
evaporated to dryness, yields a transparent glass, permanent in the air.
M. F. Capitaine, who, acting upon a suggestion made by Liebig, some twenty
years since, has recently taken up the subject of the manufacture of
soluble glass, and silicate of potash, from _farine fossile_ (an
infusorial earth), has published an account of his researches in
'Dingler's Polytechnic Journal.'[334]
[Footnote 334: See 'The Journal of the Society of Arts' for January 11th,
1878.]
Although M. Capitaine does not think that the farine will be able to
compete in cheapness with flint (where this latter is abundant) for the
preparation of the alkaline silicates, he states that it possesses the
advantage over flint of being much more soluble, and of yielding a far
more neutral glass; added to which the production of the silicate is said
to be effected with much less trouble than when flint is employed. An
important condition is, that the farine must be first well calcined, since
if the least trace of organic matter be left in it, the resulting solution
will have a yellowish or brownish tint, which will make it unsaleable.
"The lyes being prepared partly with caustic soda, and partly with
carbonate of soda, had densities ranging from 1·22 to 1·24 which were
found to be most advantageous. A reservoir furnished with mechanical
agitators, was about two thirds filled with lye, and the necessary
quantity of calcined farine added, the stirring being kept up continually.
The proportion of farine is easily calculated on the datum, that one part
of hydrate of soda dissolves about 2·8 parts of chemically pure farine,
the quality of which varies but little. Lye of the density indicated
produces a rather light solution, which presents little resistance to the
agitators. If steam is afterwards introduced the solution becomes very
rapid, when the pressure reaches about three atmospheres, and at the end
of about three hours the silica is completely dissolved.
"For the preparation of silicate of potash for surgical purposes the
farine fossile is said to be peculiarly adapted. In this case the boiling
must be continued for one or two hours longer than in the case of soluble
glass, with an addition of 10 to 15 per cent. of farine."
_Uses. &c._ Soluble glass, in solution, has been used to render textile
fabrics less combustible, as a varnish to protect stone, and as a vehicle
in fresco-painting, The soda compound (silicate of sodium) is largely used
as a dung-substitute in calico-printing, and by soap manufacturers in
place of the resinates formerly in use. 10 or 12 tons are produced weekly
in the district of South Lancashire. The potassa compound (silicate of
potassium) has been recommended as a remedy for gouty concretions by Mr
Ure.--_Dose_, 10 to 15 gr., in 6 or 8 fl. oz. of water twice a day. See
DUNGING, VARNISH, &c.
=Glass, Toughened.= _Syn._ VERRE TREMPÉ. M. de la Bastie's process for
converting ordinary, into toughened, tempered, or hardened glass, may in
general terms be said to consist in heating the glass to a certain
temperature, and then plunging it into an oleaginous bath. For the
process, however, to be successful, the observance of a number of minute
details is essential; if these be neglected failure is certain to ensue.
Thus it is found, that if the glass be insufficiently heated it will, when
immersed in the bath, fail to be affected by it, and will consequently
experience no alteration in properties. Again, if overheated, it will then
get out of shape; or, further it may be heated to the right temperature,
and yet be spoilt as it is being transferred to the bath. Moreover, the
exact composition of the bath itself, and its temperature constitute very
important conditions, the most trifling departure from which may give rise
to unsatisfactory results. All these obstacles appear to have been
overcome by M. de la Bastie, who has designed plant in the shape of
furnaces and baths, by means of which the tempering process can be carried
out, without chance of failure. When the glass is brought to the required
temperature, all that is necessary is that they should be plunged into the
bath, and instantly withdrawn. The cost of the operation is stated to be
very small.
"The process as carried out at New York is thus described:--The glass
after being run from the furnaces and moulded as usual, instead of being
put into annealing pans, is immersed in a hot bath consisting of three
parts of flaxseed oil, and one part of tallow. The bath stands at about
320°; and after remaining in this the ware is removed to a second, and
similar bath, by which it is cooled down to about 200°. Finally the pieces
are immersed in a water bath, and then dipped into a quantity of ordinary
refined burning oil. They are then cleaned, ready for packing, with
plaster of Paris powder. The work is but in its infancy, and but one small
furnace is used in the experiments. Improvements will doubtless be made,
by which the cleaning can be done more rapidly than by the powdered
plaster, probably some chemical being used for the purpose. It is supposed
that the oil works into the pores of the hot glass, and thus toughens it.
Great care has to be exercised in the final cooling by water, as too long
a contact with the air in changing from one bath to another, makes the
ware crack. Articles cooled entirely in oil retain the oil on the surface,
but are thus rendered stronger than otherwise.
This new process is very much employed in the manufacture of lamp
chimneys, though they have the disadvantage of flying into small pieces,
and with violence when they do break, which sometimes does occur."[335]
[Footnote 335: Supplement to 'Ure's Dictionary of Arts, Manufactures, &c.,
1878.]
The results so far obtained when glass is subjected to M. de la Bastie's
process are variable. In some cases the articles subjected to it possess
great toughness, and the glass bears a blow without experiencing any
fracture. In other instances, however, a slight fall or blow shivers it to
atoms. When the toughened glass under any circumstances breaks, it
possesses a disadvantage over ordinary broken glass, in distributing
itself into a great number of small, sharply angular fragments.
Another process for toughening glass, which has been patented by Herr F.
Siemens, consists in heating, and then pressing, and suddenly cooling the
glass to be hardened; but when the articles are such as are usually
moulded, the hardening and tempering are accomplished at the same time as
the pressing; thus the molten glass is run into suitable moulds, and while
still highly heated, is squeezed, the moulds effecting the necessary
cooling, a proceeding which renders the employment of the oleaginous bath
unnecessary. Mr Bauer's method for toughening glass consists in heating
ordinary glass plates so strongly that they begin to bend from softening,
and then plunging them into a liquid paraffin bath having a temperature of
200°.
Toughened glass is liable to rupture under circumstances that have not yet
been accounted for.
M. de la Bastie conceives that the fragile nature of glass is due to the
weakness of the cohesion of its particles, and that if this cohesive power
can be increased, the strength of the material will be improved in
proportion. M. de la Bastie first tried to obtain this end by forcibly
compressing the glass while in a plastic or fluid condition, but without
success; and it was only after various experiments that he was enabled to
harden the glass, by dipping it into oil or any other liquid that
permitted of being heated to a temperature considerably above that of
water.
=GLAZE.= _Syn._ GLAZING. Any coating or varnish applied to a surface to
render it smooth and glassy; any factitious, shining exterior. The
following applications of this term are the following:--
=Glaze.= In _cookery_, is commonly understood to be gravy or clarified
soups boiled until it gelatinises on cooling. It is used as a species of
varnish to cover various dishes for the table, and may be spiced and
flavoured according to the fancy of the cook. White of egg is generally
used as a glaze for pastry.
=Glaze.= In the _porcelain_ and _earthenware manufacture_, the vitreous
coating which is so essential to the beauty and utility of potter's ware.
Glazes are either white or coloured. The former, by the addition of the
colouring ingredients used for enamels, are converted into the latter.
_a._ For EARTHENWARE:--
_Prep._ 1. (With lead.) White lead (pure), 53 parts; quartz or ground
flints, 36 parts; Cornish stone, or felspar, 16 parts; white flint glass,
5 parts; reduce the whole to an impalpable powder. For common earthenware.
2. (Without lead.) Fine washed sand, 10 parts; purified potash, 8 parts;
nitre, 1 part; slaked lime, 2 parts; nitre, 4-3/4%; powder, mix, heat the
mixture in a blacklead crucible in a reverberatory furnace, till the mass
flows into a clear glass; let this cool, then reduce it to fine powder.
For glazing pharmaceutical and chemical vessels.
_b._ For PORCELAIN:--
_Prep._ (Rose.) Felspar, 27 parts; borax, 18 parts; finest siliceous sand,
4 parts; nitre, soda, and purest china clay (Cornish), 3 parts; mix, heat
to a 'frit,'[336] powder, and add of calcined borax, 3 parts.
[Footnote 336: A technical term for the half-fused mass formed by heating
together the materials of which glass is composed.]
_c._ For STONEWARE:--
1. (Ure.) White felspar, 26 parts; soda, 6 parts; nitre, 2 parts; borax, 1
part; 'frit' together as last. Of the product take 13 parts; red lead, 50
parts; white lead, 40 parts; flints, 12 parts; reduce the whole to powder
as before. For painted stoneware.
2. From common salt, which is thrown into the heated furnace containing
the ware. It is volatilised and decomposed by the joint agency of the
silica of the ware and of the vapour of water always present; hydrochloric
acid and soda are produced, the latter forming a silicate, which fuses
over the surface of the ware, and gives a thin but excellent glaze.
'SALT-GLAZED STONEWARE' is now generally used for large chemical vessels,
drain-pipes, &c.
_Obs._ Glazes must be reduced to very fine powder. For use, they are
ground with water to a very thin paste or smooth cream, into which the
articles, previously baked to the state called 'biscuit,' are then dipped;
they are afterwards exposed to a sufficient heat in the kiln to fuse the
glaze. Another method of applying them is to immerse the biscuit in water
for a minute or so, and then to sprinkle the dry powder over the moistened
surface.
=GLI'ADIN.= _Syn._ GLUTIN, VEGETABLE GELATIN. One of the proximate
principles of wheat gluten, soluble in alcohol.
=GLIADINPFLASTER= (A. L. Klose, Berlin). For rheumatism. A thin paper on
which is spread a solution of gelatin containing spirit and some acrid
substance, such as cantharides or euphorbium.--_Hager._
=GLOB'ULIN.= _Syn._ CRYSTALLIN. An albumenoid body existing in the
crystalline lens of the eye.
=GLOVE POW'DER.= _Prep._ 1. From Castile soap, dried by exposure to a warm
dry atmosphere for a few days, and then reduced to fine powder in a
mortar. Used to clean gloves.
2. Pipe-clay, coloured with yellow ochre, umber, or Irish slate q. s., and
afterwards scented with a little powdered orris root or cloves. Used to
colour gloves made of doe-skin and similar leather.
=GLOVES.= _Syn._ GANTS, Fr. Although gloves constitute a less costly
article of dress at the present day than they did during the Middle Ages,
the following information may nevertheless be sometimes found of value to
their wearers:--
GLOVE CLEANING. 1. (KID GLOVES.)--_a._ Damp them slightly, stretch them
gently over a wooden hand of appropriate size, and clean them with a
sponge dipped in benzol, recently rectified oil of turpentine, or
camphine; as soon as they are dry, withdraw them gently from the
stretcher, and suspend them in a current of air for a few days, or until
they cease to smell of the cleaning liquid used. The smell of benzol
passes off very quickly. Heat must be avoided. The cleaning liquid should
be used liberally, and the first dirty portion should be sponged off with
clean liquid.
_b._ By employing a saponaceous compound. See GANTEINE.
2. (DOE-SKIN and WASH-LEATHER GLOVES.)--_a._ Stretch them on a hand, or
lay them flat on a table, and rub into them a mixture of finely powdered
fuller's earth and alum; sweep it off with a brush, sprinkle them with a
mixture of dry bran and whiting, and, lastly, dust them well off. This
will not do if they are very dirty.
_b._ Wash them in lukewarm soft water, with a little Castile or curd soap,
ox-gall, or bran tea; then stretch them on wooden hands, or pull them into
shape without wringing them; next rub them with pipe-clay and yellow
ochre, or umber, or a mixture of them in any required shade made into a
paste with ale or beer; let them dry gradually, and, when about half dry,
rub them well, so as to smooth them and put them into shape; when they are
dry, brush out the superfluous colour, cover them with paper, and smooth
them with a warm (not hot) iron.
GLOVE DYEING. LEATHER GLOVES, if not greasy, may be dyed with any of the
ordinary dyes by brushing the latter over the gloves stretched out smooth.
The surface alone should be wetted, and a second or third coat may be
given after the former one has become dry. When the last coat has become
thoroughly dry, the superfluous colour should be well rubbed out, a smooth
surface given them by rubbing them with a polished stick or piece of
ivory, and the whole gone over with a sponge dipped in white of egg.
=Gloves, Cosmetic.= _Syn._ GANTS COSMETIQUES. These are mock kid or
lambskin gloves rubbed over, on the inside, with the following
composition:--Spermaceti cerate, 3 oz.; melt, add of balsam of Peru, 1/2
dr., stir for 5 minutes, and, after a few minutes' repose, pour off the
clear portion; to this add of oil of nutmeg, 15 drops; oil of cassia and
essence of ambergris, of each 6 drops; and stir until cold. Used by ladies
to soften the hands and to prevent or cure chilblains and chaps. They are
commonly worn all night in bed.
=GLUCI'NUM.= Gl. _Syn._ BERYL'LIUM. The metallic base of glucina. It was
first obtained by Wöhler, in 1828, by a similar process to that adopted
for aluminum, a metal which it greatly resembles. See ALUMINUM.
=Gluci'num, Oxide of.= _Syn._ GLUCINA, BERYLLIA. A pulverent white
substance, found as silicate in the beryl, emerald, &c.
_Prep._ The beryl, in fine powder, 1 part; carbonate of potassium, 3
parts; expose the mixture to a strong red heat for half an hour, dissolve
the calcined mass in hydrochloric acid, and evaporate the solution to
dryness; redissolve the residuum in very dilute hydrochloric acid, and
precipitate with pure ammonia; wash the precipitate well, digest it with a
large quantity of carbonate of ammonium, filter, and boil the solution as
long as carbonate of glucinum subsides. By exposure to a red heat the
carbonic acid may be expelled, and the earth rendered anhydrous.
_Prop., &c._ Glucina closely resembles alumina, from which, however, it is
distinguished by its solubility when freshly precipitated in a cold
solution of carbonate of ammonia, from which it is again thrown by
boiling. Glucina is classed with the earths. The beryl contains 14% of
this substance.
=GLU'COSE.= See SUGAR (Grape).
=GLUE.= _Syn._ GLUTEN, GLUTINUM, L.; COLLE, COLLE FORTE, Fr. Inspissated
animal jelly, or gelatin, used as a cement.
_Prep._ Glue is principally prepared from the parings and waste-pieces of
hides and skins, the refuse of tanneries, and the tendons and other offal
of slaughter-houses. These substances, when intended for the glue-maker,
are steeped for 14 or 15 days in milk of lime, then drained, and dried by
exposure to the air. This constitutes what is termed the 'cleansing' or
'preparation,' and in this state the 'glue pieces,' as they are called,
may be kept for a long time, and transported to any distance without
suffering decomposition. Before conversion into glue, they are usually
again steeped in weak milk of lime, and next well washed and exposed to
the air for 24 to 30 hours. They are then placed in a copper boiler two
thirds filled with water, and furnished with a perforated false bottom, to
prevent them from burning, and as much is piled on as will fill the vessel
and rest on the top of it. Heat is next applied, and the whole gently
boiled or simmered together, until the liquor on cooling forms a firm
gelatinous mass. The clear portion is then run off into another vessel,
and a very small quantity of alum (dissolved) added; here it is kept hot
by a water bath, and allowed to repose for some hours to deposit its
impurities, after which it is run into the 'congealing boxes,' and placed
in a cool situation. The next morning the cold gelatinous masses are
turned out upon boards wetted with water, and are cut horizontally into
thin cakes with a stretched piece of brass wire, and then into smaller
cakes with a moistened flat knife. The latter are placed on nettings to
dry. The dry cakes of glue are next dipped one by one into hot water, and
slightly rubbed with a brush wetted with boiling water, to give them a
gloss; they are, lastly, stove-dried for sale. This furnishes the palest
and best glue.
As soon as the liquor of the first boiling has drained off, the
undissolved portion of skins, &c., left in the copper is treated with
fresh water, and the whole operation is repeated again and again, as long
as any gelatinous matter is extracted. In this way a second and other
inferior qualities of glue are obtained. The product from dried
glue-pieces is about 50%.
_Var._ These chiefly depend on the care with which the process is
conducted. HATMAKERS' GLUE is prepared from the tendons of the legs of
neat cattle and horses. It is brown, opaque, and soft; and grows moist in
damp weather, but it does not render felt brittle like the other
varieties. FISH GLUE is made in like manner from various membranous and
solid parts of fishes. PARCHMENT GLUE is prepared from shreds or shavings
of parchment, vellum, white leather, &c., dissolved by boiling them in
water. It is scentless, and nearly colourless.
_Qual._ The best glue is transparent, nearly colourless, and tasteless,
has very little smell, even when melted, and is extremely adhesive. The
presence of more than a trace of alum is objectionable; an undue quantity
may be easily detected by the usual tests. The strongest glue is that
obtained from skins, more especially from the hides of oxen and cows.
That obtained from the bones, cartilages, and tendons, is weaker.
=Glue, Liq'uid.= _Prep._ (Dumoulins.) Soft water, 1 quart; best pale glue,
2 lbs.; dissolve in a covered vessel by the heat of a water bath, cool,
and add, gradually, of nitric acid (sp. gr. 1·335), 7 oz.; when cold put
it into bottles. Very strong, and does not gelatinise. For the 'LIQUID
GLUE' sold in the shops, see CHINESE CEMENT.
=Glue, Marine.= _Prep._ 1. India rubber (cut small), 1 part; coal tar or
mineral naphtha, 12 parts; digest in a covered vessel with heat and
agitation, and when the solution is complete, add of powdered shell-lac,
20 parts; continue the heat and stirring until perfect liquefaction has
taken place, and pour the fused mass, whilst still hot, on slabs of
polished metal or stone, so as to form thin sheets. For use, it is heated
to its melting-point (248° to 250° Fahr.) in an iron vessel, and applied
in the liquid state with a brush. Employed in ship-building, &c.
2. Caoutchouc, 15 to 20 gr.; chloroform, 2 fl. oz.; dissolve, and add of
powdered mastic, 1/2 oz. It must be kept well corked and in a cool place,
to prevent loss by evaporation. Used for small, fine work.
=Glue, a New.= Ordinary glue is dissolved in nitric ether, and a little
bit of caoutchouc added. This solution forms a very strong glue, and does
not get thick or pasty. ('Dengler's Journal.')
=Glue, Port'able.= _Syn._ BANK-NOTE GLUE. MOUTH G., INDIAN G.; COLLE À
BOUCHE, Fr. _Prep._ From the best pale glue, 1 lb.; water, q. s.; dissolve
in a double glue-pot or water bath, and of pale-brown sugar, 1/2 lb.,
continue the heat until the mixture is complete, and pour it into moulds;
or pour it on a marble slab, and when cold cut it into small pieces and
dry them in the air. This glue is very useful to draughtsmen, architects,
&c., as it dissolves almost immediately in warm water, fastens paper, &c.,
without the process of damping, and may be softened for many purposes with
the tongue. When great strength not required, 4 oz. more of sugar may be
used.
=GLU'TEN.= _Syn._ GLUTIN. A peculiar substance found in the grain of
wheat. It is composed of true vegetable fibrin and a small quantity of
gliadin. It is prepared by washing paste made of the flour of wheat or rye
in successive waters until all starchy matter is removed. The paste may be
conveniently enclosed in a bag of fine linen during the washing.
_Prop., Uses._ Gluten is believed to be eminently nutritious. It is the
presence of gluten in wheaten flour that imparts to it its viscidity or
tenacity, and confers upon it its peculiar excellence for the manufacture
of MACARONI, VERMICELLI, and similar pastes. The superiority of wheaten
over other bread depends upon the greater tenacity of its dough, which
during the fermentation is puffed up by the evolved carbonic acid, and
retained in its vesicular texture so as to form a light loaf.
Gluten is greyish coloured, and extensible whilst fresh and moist, like
caoutchouc. It turns blue when mixed with guaiacum resin.
=Gluten Bread.= _Prep._ 1. From wheat flour which has been deprived of
about 2-3rds of its starch by washing it with water.