APPLICATION OF SOLUBLE GLASS TO WOOD WORK. 
Ml 
fixed fusible salts are capable of performing, 
ifthey be, in addition, composed of substances 
incapable of yielding theii oxygen at a low red 
heat, to either carbon or hydrogen. These 
salts melt as the vegetable matter becomes 
heated; they form upon it a coat impenetra- 
ble to the air, and either prevent altogether, 
or limit its combustion. The phosphate and 
borate of ammonia have such a character, but 
they are so readily soluble in cold water, as to 
be liable to objections which cannot be urged 
against soluble glass. 
Although soluble glass is of itself a good 
preservative from fire, it fulfils the object bet- 
ter when it is mixed with another incombus- 
tible body in powder. In this case the solu- 
tion of glass acts in the same manner as the 
oil of painters. The several coats have more 
body, become more solid, and more durable; 
and, if the substance which is added be of 
proper quality, coagulate by the action of fire 
into a strongly adhesive crust. Clay, whit- 
ing, calcined bones, powdered glass, &c. may 
all be employed for this purpose ; but we can- 
not yet say with certainty which of them is to 
be preferred. A mixture of clay and whiling 
appears to be better than either used separately. 
Calcined bones form with soluble glass a very 
solid and adhesive mass. Litharge, which, 
with the glass, makes an easily fusible mix- 
ture, does not give a product fitted for coat- 
ing wood, as the mixture contracts in drying ; it 
therefore cracks, and is easily separated. Flint 
glass, and crude soluble glass, are excellent 
additions. The latter ought to be exposed to 
the air after it is pulverized, 'in order to attract 
moisture. If it he mixed with solution, and 
be then applied to any body whatever, it in 
a short lime forms a coating as haid as stone, 
which, if the glass be of good quality, is unal- 
teiable by exposure, and resists fire admirably. 
The scoriae of iron and lead, felspar, fluor, 
may all be employed with soluble glass; but 
experience alone can decide which of these 
substances is best, and in what proportion they 
are to be employed. We should advise that 
the first coat should always be a simple solu- 
tion of the glass ; and that a similar solution be 
applied over coats composed of its mixture 
with other substances, particulaily vvhen such 
coat is uneven and rough. 
The last named substances form a solid and 
durable coating, which suffers no change by 
exposure to the air, does not involve any 
great expense, and is readily applied. But, in 
order that it may not fail, particular care is to 
be taken both in preparing and employing it. 
In order to cover wood and other bodies 
with it, the solution must be made of a pure 
glass, for otherwise it would effloresce and 
finally fall off. However, a small degree of 
impurity is not injurious, although after a 
few days a slight efflorescence will appear ; 
this may be washed off by water, and will 
not show itself a second time. When a 
durable covering is to be applied to wood, too 
strong a solution must not be employed at 
first; for in this case it will not he absorbed, 
will not displace the air from the pores, 
and in consequence will not adhere strongly. 
It is a good plan to rub the brush several 
times over the same place, and not to spread 
the coating too lightly. For the last coats 
a more concentrated solution may be employ- 
ed, still it must not be too thick, and must 
be spread as evenly as possible. Each coat 
must be thorougly dry before another is ap- 
plied ; and this will take, in warm and dry 
weather, at least twenty-four hours. After 
two hours the coat appears to be dry, but is 
still in a state to be softened by laying on 
another. The same inconvenience will then 
arise, which occurs when a thick coat of a 
concentrated solution is applied ; the coat will 
crack, and does not adhere. This, however, 
is only the case when potassa is the base of 
the glass, for that formed from soda does not 
appear to crack. 
In applying soluble glass to the wood- work 
of the theatre at Munich, 10 per cent, of yel- 
low clay {ochre?) was added. After six 
months, the coat had suffered but little 
change ; it was damaged only in a few places, 
where it had need of some repair. This arose 
from a short time only having been allowed 
for the preparation and application of the 
glass, and they were therefore done without 
proper attention. 
When this mode is employed for preserving 
a theatre from fire, it is not enough to cover 
the woodwox’k, it is also necessary to preserve 
the scenery, which is still more exposed to 
danger. None of the methods yet proposed 
for this purpose appears so advantageous as 
soluble glass, for it does not act on vegeta- 
ble matter, and completely fills up the spaces 
between the thread ; it fixes itself in the web, 
in such a way that it cannot be separated, and 
increases the durability of the fabric. The 
firmness which it gives to stuffs does not 
injure them for use as curtains, because it 
does not prevent them from being easily 
rolled. So far as the painting of scenes 
is concerned, the glass forms a good ground 
for the colours. To prevent the changes 
which some colours, Prussian blue and lake 
for instance, might undergo from the alka- 
line matter, it will he necessary before 
painting to apply a coat of alum, and then 
one of whiting. 
There is no great difficulty in applying 
soluble glass to cloths, still this operation is 
not so easy as might at first he imagined. 
It is not sufficient to coat or dip them in the 
solution ; they still require after this opera- 
tion to he subjected to pressure. This object 
might perhaps be best attained by passing 
them between rollers plunged in the solution. 
When a cloth is only coated with soluble 
glass, is put into the fire, it will remain 
incandescent after it is taken out. This is 
not the case when it has been properly im- 
pregnated with the solution. A still better 
purpose is answered in this case, wh^en li- 
tharge has been added to the solution. The 
stuff' in drying yields to the shrinking of the 
mixture, and becomes inseparable from it, 
which is the reverse of what happens when it 
is applied to wood. A single part of litharge 
in fine powder is sufficient for fourteen parts of 
concentrated liquor. 
