m sil 
Proportion s 
Heat. 
| Effect. 
50 Silica 
50~ Barytes 
143 
1 
A hard mass not 
melted. 
20 Silica 
80 Barytes 
148 
The edges were 
melted into a 
pale green vh 
matter between a 
porcelain and e- 
namel. 
f25 Silica 
75 Barytes 
150 
Melted into a 
somewhat porous 
porcelain. 
33 Silica 
06 Barytes 
150 
Melted into a 
yellowish and 
partly greenish 
white porous por- 
celain. 
St rontian and silica combine with each 
other nearly in the same manner. 
There is also an affinity between silica and 
lime. When lime-water is poured into a so- 
lution of silica in potass, a precipitate ap- 
pears, as Stucke discovered. This precipi- 
tate is a compound of silica and lime. These 
two earths may be combined also by means 
of heat. They form a glass, provided the 
quantity of lime is not inferior to that of silica. 
The etfect of heat upon these earths, mixed 
in various proportions, will appear from the 
following experiments of Mr. Kirwan : 
Proportions. 
Heat. 
Effect. 
40 Lime 
s > 0 Silica 
150° Wedg. 
Melted into a 
mass of a whit- 
ish colour, semi- 
transparent at 
the edges, and 
striking fire, 
though feebly, 
with steel : it 
was somewhat 
between porce- 
lain and enamel. 
5»0 Lime 
50 Silica 
Ayellowishwhite 
loose powder. 
SO Lime 
SO Silica 
Not melted, 
formed a brittle 
mass. 
Equal parts of magnesia and silica melt 
with great difficulty into a white enamel 
when exposed to the most violent heat which 
can be produced. r i hey are infusible in in- 
ferior heats, in whatever proportion they are 
mixed. 
There is a strong affinity between alumina 
and silica. When equal portions of silicated 
and aluminated potass are mixed together, a 
brown z@ne immediately appears, which may 
be made, by agitation, to pass through the 
whole liquid. After standing about an hour, 
the mixture assumes the consistence of jelly. 
When formed into a paste with water, and 
dried, they cohere and contract a consider- 
able degree of hardness. When baked in the 
temperature of 160° Wedgewood, they be- 
come very hard, but do not fuse. Achard 
found them infusible in all proportions in a 
heat probably little inferior to 150° of Wedge- 
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wood. But when exposed to a very strong 
heat, they are converted into a kind of opaque 
glass, or rather enamel. Porcelain, stone 
ware, brick, tiles, and other similar substances, 
are composed chiefly of this compound. 
Mixtures of silica and alumina in various 
proportions constitute clays ; but these are 
seldom uncontaminated with other ingredi- 
ents. 
It follows from the experiments of Achard, 
that equal parts of lime, magnesia, and silica, 
may be melted into a greenish-coloured glass, 
hard enough to strike fire with steel ; that 
when the magnesia exceeds, either of the other 
two, the mixture will not melt; that when 
the silica exceeds, the mixture seldom melts, 
only indeed with lime in the following propor- 
tions; three silica, two lime, one magnesia, 
which formed' a porcelain; and that when 
the lime exceeds, the mixture is generally fu- 
sible. 
A mixture of silica and alumina may also 
be combined with barytes or strontian by 
means of heat. The mixture melts readily 
into a greenish-coloured porcelain. 
F rom the experiments of Achard and Kir- 
wan, we learn that, in mixtures of lime, silica, 
and alumina, when the lime exceeds, the 
mixture is generally fusible either into a glass 
ora porcelain, according to the proportions. 
That if the silica exceeds, the mixture is fre- 
quently fusible into an enamel or porcelain, 
and perhaps a glass; and that when the alu- 
mina exceeds, a porcelain may often be at- 
tained, but not a glass. 
As to mixtures of magnesia, silica, and alu- 
mina, when the magnesia exceeds, no fusion 
takes place at 150°. When the silica ex- 
ceeds, a porcelain may often be attained ; 
and three parts silica, two magnesia, and one 
alumina, form a glass. When the alumina ex- 
ceeds, nothing more than a porcelain can be 
produced. 
Achard found that equal parts of lime, 
magnesia, silica, and alumina, melted into a 
glass. They fused also in various other pro- 
portions, especially when the silica predomi- 
nated. 
Silica differs from all the other earths in not 
combining with any of the acids except the 
fiuoric, phosphoric, and boracic; to which, 
perhaps, we may add the muriatic. 
Silica is one of the most important of the 
earths. It is the chief ingredient of those 
stones which seem to constitute the basis of 
this terrestrial globe. It is an essential in- 
gredient in mortar, in all kinds of stone ware, 
and in glass. 
SILK, in natural history, is the production 
of different species of caterpillars. The pba- 
Isena, or bombyx mori, is most commonly pro- 
pagated for that purpose in Europe; but the 
phalena atlas yields a greater quantity. See 
Bombyx, and PhaljEna. A similar sub- 
stance, indeed, is yielded by the greater num- 
ber of the tribe of caterpillars. It is found 
inclosed in two small bags, from which it is 
protruded in fine threads to serve the insect 
for a covering during its chrysalis state. The 
webs of spiders are obviously of the same 
nature with silk ; though their fibres, at least 
in this country, are finer and weaker. Reau- 
mur and other naturalists ascertained, that 
the larger species of spiders spun webs suffi- 
ciently strong to b.e manufactured, and that 
S I L 
the produce was neither inferior in beauty 
nor in strength to the silk of the silkworm. 
See Aranea. 
The silkworm is a native of China, and 
feeds on the leaves of the white mulber- 
ry. That industrious nation was acquaint- 
ed with the manufacture of siik from the 
most remote ages; but it was scarcely 
known in Europe before the time of Augus- 
tus. Its beauty attracted the attention of the 
luxurious Romans ; and after the effeminate 
reign of Elagabulus, it became a common ar- 
ticle of dress. It was brought from China at 
an enormous expenee, manufactured again 
by the Phoenicians, and sold at Rome for its 
weight of gold. In the reign of Justinian this 
commerce was interrupted by the conquests 
of the Scythian tribes, and all attempts to 
procure it failed till two Persian monks had 
the address to convey some of the eggs of tin* 
insect from China to Constantinople, conceal- 
ed in the hollow of a cane They were 
hatched, and the breed carefully propagated. 
This happened in 555; and some years after 
we find that the Greeks understood the art of 
procuring and manufacturing silk as well as 
the Orientals. Roger, king of Sicily, brought 
the manufacture to that island in 1 130, for- 
cibly carrying off the weavers from Greece, 
and settling them in Sicily. From that island 
the art passed into Italy, and thence into 
France: and the revocation of the edict of 
Nantz established the manufactory of silk in 
Britain. 
Silk, as spun by the animal, is in the state 
of fine threads, varying in colour from white 
to reddish yellow. It is very elastic, and has 
considerable strength, if we consider its small 
diameter. It is covered with a varnish, to 
which its elasticity is owing. This varnish is 
soluble in boiling water; but alcohol does 
not act upon it. Hence it has been compar- 
ed to a gum, though it approaches much 
nearer to a gelatine; since Bertbollet has 
shewn that it is precipitated by tan and by 
nniriat of tin. It differs, however, from gela- 
tine in several particulars. Alum throws if 
down of a dirty white, suiphat of copper of a 
dark brown, and suphat of iron of a brown 
colour. When the water is evaporated, the 
varnish is obtained of a black colour, brittle, 
and of a shining fracture. Its weight is nearly 
one-third of the raw silk from which it was ex- 
tracted. It may be separated from silk by 
soap as well as water, and the soap leys con- 
taining it soon putrefy. 
Besides the varnish, silk contains another 
substance to which it owes its yellow colour. 
This, substance possesses the properties of re- 
sin. It is yellow’, soluble in alcohol, and in a 
mixture of alcohol and muriatic acid. Beaume 
has ascertained, that by this last mixture it 
may be separated completely, and the silk 
deprived of it assumes a tine white colour. 
The chemical properties of silk itself have 
been but imperfectLy examined. It is not 
acted on by water or alcohol, has no taste, 
and is but imperfectly combustible ; though 
fire rapidly blackens and decomposes it. 
When distilled, it yields, according to Neu- 
mann, an uncommonly great proportion of 
ammonia. 
The fixed alkalies dissolve it by the assist- 
ance of heat ; and it is not unlikely that they 
form with it an animal soap. 
It is dissolved likewise' by sulphuric and 
muriatic acids, and by nitric acid. By .th# 
