The Sun.
London, England, 1854-09-20 00:00:00

known silicates, whether natural, as feldspar, mica,
clay, &c., or artificial, as glass, &c., are the results.
The common forms of insoluble glass are produced
by the union of silica with more than one base ; but,
when combined with an alkaline base only, silica forms
a soluble glass, the degree of solubility of which de-
pends on the proportion which the siliceous acid bears
to this alkaline base. This soluble silicated alkali (or
water-glass) may be prepared by various processes. If
sand be used, 15 parts of fine sand, thoroughly incor-
porated with 8 parts of carbonate of soda, or with 10 of
carbonate of potass and one of charcoal fused in a fur-
nace, will produce a silicated alkali which is soluble in
boiling water. Messrs. Ransomes obtain this silicated
alkali by dissolving broken flints in a solution of caustic
alkali at a temperature nf 300 deg. Fah. And, more
recently, Mr. Way has observed that the sand which he
has described will combine with caustic alkali at boil-
ing heat, also producing a water-glass.
This water-glass has been applied to several important
purposes, three of which were specially noticed.
I. To protect building-stones from decay. The
stone surfaces of buildings, by being exposed to the
action of the atmosphere, become liable to disin-
tegration from various causes. Moisture is ab-
sorbed into their pores. The tendency of their par-
ticles to separate, in consequence of expansion and
contraction, produced by alternation of tempera-
ture, is thus increased. Sulphurous acid is always pre-
sent in the atmosphere of smoke-burning cities, and can-
not but corrode the calcareous and magnesian ingredi-
ents of oolites and dolomites. It is true that good stone
resists these sources of injury for an indefinite time, but
such a material is rarely obtained. As a preventive of
destruction, whether arising from physical or chemical
causes, it has been proposed to saturate the surfaces of
the stones with a solution of the water-glass.
It is well known that the affinity of silica for alkali is
' so feeble that it may be separated from this base by
the weakest acids, even by carbonic acid. According to
the expectation of those who recommend the silication
of stone, the carbonic acid of the atmosphere will set
the silica free from the water-glass, and the silica, thus
separated, will be deposited within the pores and around
the particles of the stone. The points of contact of these
particles will thus be enlarged, and a sort of glazing of
insduble silica will be formed sufficient to protect the
stone against the effects of moisture, &c. This cause
of protection applies chiefly to sandstones. But
whatever carbonate of lime or carbonate of magnesia
enters notably into the composition of the building-
scone, then an additional chemical action, also protec-
tive of the stone, is expected to take place between
these carbonates and the water-glass. Kuniman re-
marks—" Toutes les foie que l'on met en contact un sel
insoluble avec la dissolution d'un eel dont l'acide pent
former avec la base du sel insoluble un eel plus insoluble
encore, it y a echange ; !Dais les plus sovent cet &hang*
n'est qua partiel." In consequence of this " partial
change" an insoluble salt of lime may be looked for
whenever a solution of water-glass is made to act on the
carbonate of lime or carbonate of magnesia existing in
oolitic or dolomitic building-stones.
This expectation, however, has not been altogether
sanctioned by experiment. A gentleman, eminently
conversant with building materials, immersed a piece of
Caen stone in a solution of silicate of potass in the
month of January, 1849. This fragment, together
with a portion of the block from which it had been
separated, was placed on the roof of a building, iu or-
der that it might be fully exposed to the action of atmo-
sphere and climate. After four years the silicated and
the unsilicated specimens were found to be both in the
same condition—both to be equally corroded. These
specimens were exhibited in the theatre of the insti-
tution. But whatever ultimate results may en-
sue from the process, the immediate effects on the
stone are remarkable. Two portions of Caen stone were
exhibited, one of which had been soaked in a solution
of water-glass two months before. The surface of the
unsilicated specimen was soft, readily abraded when
brushed with water, and its calcareous ingredients dis-
solved in a weak solution of sulphurous acid. The sili-
cated surface, on the other hand, was perceptibly hard,
and resisted the action of water and of dilute acid when
similarly applied.
11. Another proposed use of the water-glass is that of
hardening cements, mortars, &c., so as to render them
impermeable by water.
Four years since Anthon of Prague proposed several
applications of the water-glass. Among others he sug-
gested the rendering mortars waterproof. lie also sug-
gests that this substance might be beneficially employed
as a substitute for size in whitewashing and staining
walls. It was demonstrated by several experiments
that carbonate of lime mixed up with a weak solution of
water-glass, and applied as a whitewash to the surface,
was not washed off by sponging with water, and that
common whitewash, laid on in the usual manner with
size, was rendered equally adhesive when washed over
with water-glass.
M. The Stereocbrome of Fuchs.

The formation of an insoluble cement by means of the
water-glass, whenever the carbonic acid of the atmosphere
acts on this substance, or whenever it is brought in con-
tact with a lime-salt, has been applied by Fuchs to a most
important purpoa3. The stereochrome is essentially the
process of fresco secco invested with the capability of
receiving and perpetuating works of the highest artistic
character, and which may be executed on a vast scale.
Fuchs' method is as follows :

" Clean and washed quartz-sand is mixed with the
smallest quantity of lime which will enable the plasterer
to place it on the wall. The surface is then taken off
with an iron scraper, in order to remove the layer formed
in contact with the atmosphere, the wall being still moist
during this operation. The wall is the❑ allowed to dry ;
after drying it is just in the state in which it could be
rubbed off by the finger. The wall has now to be fixed,
i. e., moistened with water-glass. (An important point
is not to use to use too much water-glass in moistening
the wall.) This operation is usually performed with a
brush. The wall must be left in such a condition as to
be capable of receiving colours when afterwards painted
on. If, as frequently happens, the wall has been too
strongly fixed, the surface has to be removed with porn-
mice and to be fixed again. Being fixed in this manner,
the wall is suffered to dry. Before the painter begins
he moistens the part on which he purposes to work with
distilled water, squirted on by a syringe. He then
paints; if he wishes to repaint any part, he rnoistens again.
As soon as the picture is finished, it is syringed over
with water-glass. After the wall is dry, the syringing
is continued as long as a wet sponge can remove any of
the colour. An efflorescence of carbonate of soda some-
times appears on the picture after its completion. This
may be removed, either by syringing with water, or may
be left to the action of the atmosphere." Not to dwell
on the obvious advantages possessed by the stereochrome
over the real fresco (such as its admitting of being re-
touched and its dispensing with joinings), it appears that
damp and atmospheric influences, notoriously destruc-
tive of real fresco, do not injure pictures executed by this
process.
The following crucial experiment was made on one of
these pictures. It was suspended for 12 months in the
open air, under the principal chimney of the New Mu-
seum at Berlin ; "during that time it was exposed to
sunshine, mist, snow, and rain," and nevertheless " re-
tained its full brilliancy of colour.
The stereochrome has been adopted on a grand scale
by Kaulbach, in decorating the interior of the grand
national edifice at Berlin already alluded to. These de-
corations are now in progress, and will consist of histo-
rical pictures (the dimensions of which are 21 feet in
height and 2-1 i in width), single colossal figures, friezes,
arabesques, chiaroscuro subjects, &c. On the effect of
the three finished pictures, it has been remarked by one
whose opinion is entitled. to respect, that they have all
the brilliancy and vigour of oil paintings, while there is
the absence of that dazzling confusion which new oil
paintings are apt to present, unless they are viewed in
one direction, which the spectator has to seek for.
Mr. A. Church has suggested that if the surface of
ool►tic stones (such as Caen stone) is found to be pro.
tected by the process already described, it might be
used, as a natural intonaco, to receive coloured designs,
&c., for external decorations ; the painting would then
be cemented to the stone by the action of the water-
glass. _ _ _

- Mr. Church also executed designs of leaves on a sort of
terracotta, prepared from a variety of Way's silica rock,
consisting of 75 parts clay and 25 of soluble silica. This
surface, after being hardened by heat, is very well adapted
for receiving colours in the first instance, and for retain.
ing them after silicatiou.

No. 4.

LETTER FROM THE RIGHT HON. THE SECRETARY OF STATE

FOR THE HOME DEPARTMENT.

Whitehall, July 20, 1854.
Sir,—l have received the Queen's commands to notify
to you that her Majesty has been graciously pleased to
approve of the tenth report of the commissioners on
the fine arta transmitted in your letter of the 13th
instant.

Her Majesty has directed the Lords Commissioners of
the Treasury to submit to Parliament estimates in con-
formity with the recommendations contained in the
report.—l am, &c., (Signed) PALMERSTON.
Sir C. L. Eastlake, Palace of Westminster,