Sol′u-ble glass.
Also generally known as
water-glass. An alkaline silicate which is soluble in water, but remains unaffected by ordinary atmospheric changes.
It was first observed by
Von Helmont, in 1640, and was subsequently, in 1648, made by Glauber from potash and silica, and by him termed fluid silica.
It is employed as a fire-proof coating for various substances, and latterly important as a constituent of artificial stone.
All glass is chemically a silicate of some alkaline or metallic oxide; but those kinds alone in which the silica is combined with soda or potash without a third substance being employed, are soluble in water.
For much that is valuable in the preparation and application of water-glass or soluble glass, we are indebted to
Dr. Johann Fuchs, of
Munich.
He announced his success in 1825, and published a pamphlet shortly before his death, in 1856.
Mr. Ransome, of
Ipswich, England, has also contributed to the success of the process.
It forms an essential ingredient of
Ransome's artificial stone.
It has been used in painting on glass; surfacing stone, wood, and other materials to render them water-proof; covering roofs, for the same purpose; glazing scenery or paintings; as a menstruum for carbon, in making indelible ink. It has been used to arrest the wear of the stone, on the
Cathedral of Notre Dame,
Paris, and the new houses of Parliament,
Westminster, England.
Soluble glass may be prepared by either the
wet or
dry way. In the former, flint nodules are broken and calcined, added to a solution of caustic potash or soda, and exposed for a time to intense heat.
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In the dry way the constituents are fused together in the solid state, and afterward dissolved.
Four kinds are employed, known as the
potash, soda, double, and
clear silicates.
The first is composed of 15 parts pulverized quartz, 10 purified potash, 1 pulverized charcoal.
These are well mixed, and exposed to a strong heat in a glass-melting pot until thoroughly fused.
When cool, the mass is broken in pieces, and boiled for about 3 hours in 5 times its weight of water, more water being occasionally added to replace that lost by evaporation.
When thoroughly dissolved, it is viscid, and may be used in this state or still farther diluted.
It should be preserved in well-stopped vessels.
The soda silicate is composed of 45 parts pure quartz, 23 anhydrous carbonate of soda, and 3 pulverized charcoal; these are fused and treated in the manner just described.
By substituting the anhydrous sulphate for the carbonate of soda and using about 8 times more charcoal, a cheaper compound is produced.
Buchner's formula for soda water-glass is, pulverized quartz, 100; calcined glauber salts, 60; carbon, 15 to 20 parts.
The double silicate is composed of 100 parts quartz, 28 purified potash, 22 neutral anhydrous carbonate of soda, and 6 powdered charcoal.
This mixture fuses more easily than either of the others.
In its place three parts of the first and two of the second solutions, which mix freely together, may be employed.
The mixed silicate forms with sand an excellent cement, converting it into a stone-like mass, and is also useful for filling cracks in walls.
Marble dust, or chalk made into a paste with water, dried and saturated with the silicate, forms a mass little inferior in hardness to marble, and capable of taking a fine polish.
A mixture of marble dust and the silicate of soda forms a cement which adheres either to stone or wood.
Oxide of zinc combines with the silicate, forming a paste, which may be rolled into sheets resembling slate.
The
clear silicate is applied for fixing the colors of pictures.
It is made by fusing 3 parts pure anhydrous carbonate of soda with 2 of powdered quartz, the compound being boiled as before.
This is kept in a concentrated solution, and for use 1 part is mixed with 4 parts of the concentrated potash silicate completely saturated with quartz.
The
fixing water-glass of
Von Fuchs is used for fixing the colors in stereochromy, and is composed of silica well saturated with potash, water-glass, and a silicate of soda, obtained by melting together 3 parts calcined soda and 2 of pulverized quartz.
The prepared water-glass of commerce is made by boiling the powdered water-glass in water, forming solutions known as of 33° and 66° respectively, those amounts denoting the respective amounts by weight of solid water-glass contained in 100 parts of the solution.
Wall paintings are fixed by water-glass in a much more durable manner than ordinary frescoing.
The ground may be similar to that employed for frescos, or a water-glass mortar may be employed, composed of about 10 parts dry sharp sand, 3 quicklime, and 2 dry pulverized chalk or limestone, worked to the proper consistency with dilute water-glass.
Water-colors, not too heavily laid on, are applied, care being taken to reject organic colors, which are fugitive, and such others as have a tendency to combine with the glass.
When the picture is finished, the whole is fixed by an application of the water-glass in thin jets from a rose nozzle syringe.
The process has received the name of
stereochromy.
Water-glass is also used as a vehicle for painting upon glass, various metallic oxides and salts being employed as the coloring mediums, the compound becoming chemically united with the silicious surface of the glass, so as to resist the action of water.
It also is made up into a paint or cement with clay, whiting, chalk, calcined bones, powdered glass, or litharge in various combinations.
It makes a very strong and adhesive compound.
The theater of
Munich, Bavaria, was painted with a composition in which 10 per cent of yellow clay was added to soluble glass.
Dobereiner's formula gives a soluble glass suitable for coating woodwork:
| Carbonate of potash | 70 |
| Carbonate of soda | 54 |
| Ground flints or quartzose sand | 152 |
| —– |
| 276 |
Another formula given is:—
| Carbonate of soda (or carbonate of potash, 10） | 8 parts. |
| Pure sand | 15 parts. |
| Charcoal | 1 part. |
| —– |
| 24 parts. |
The product dissolves in boiling water.
The addition of hydrochloric acid causes the silica to separate as a transparent, tremulous jelly.
This is hydrate of silica, is not soluble in water or acids, may be preserved in a gelatinous condition, but crumbles when dried.
