SIL 
space of an hour, although it was occasion- 
ally stirred with a glass rod ; but at the 
end of that time the whole mass assumed 
the appearance of a thick, opaque white 
jelly. Wlien the silica and alumina are 
mixed together, and formed into a paste 
with water, and exposed to heat, they 
strongly cohere, and assume a considerable 
degree of hardness. This compound forms 
the basis of all kinds of pottery and por- 
celain. 
Barytes and strontian in some degree 
dissolve silica as the alkalies do. Two^ 
hundred parts of strontian, with sixty ot 
silica, heated intensely in a crucible for an 
hour, produced a grey sonorous rifty mass, 
with only a slight caustic taste. This being 
boiled in water, was partly dissolved, but 
could not be crystallized. Saturated with 
nitric acid, it gave, by evaporation, a copi- 
ous jelly, which was pure silex. A similar 
result was obtained when barytes was used 
instead of strontian. 
SILIQUA, in botany, a species of pod, 
in which the seeds are alternately fixed to 
either suture or joining of the valves ; in 
this it differs from the legumen, which has 
its seeds attached to one suture only. This 
kind of seed vessel is found in all the 
class Tetradynamia of Linnaeus. See Le- 
GUMEN. 
SILIQUOS.T:, in botany, the name of 
the thirty-nintlr order in Limraeus’s Frag- 
ments of a Natural Method, consisting of 
plants that have a siliqua for a seed vessel. 
It is divided into two sections : 1. Those 
which have cross-shaped flowers with tong 
pods, as the brassica, cabbages, raphauus, 
radish; sinapis, mustard, &c. 2. Those 
with cross-shaped flowers with short round 
pods, as the iberis, candy-tuft. This order 
chiefly furnishes biennial aud perennial 
herbs of an irregular figure. The roots are 
long, branched, crooked, and fibrous ; those 
of the turnip and radish nre succulent and 
fleshy ; the flowers are hermaphrodite, 
and in the greater number disposed in a 
spike at the extremity of the branches. 
They are easily rendered double by culture. 
Ti.-^ stamina are six in number, two of 
which are of tlie length of the calyx, and 
the remaining four somewhat longer, but 
shorter than the petals. The seed-vessel, 
as we have observed, is a long pod in plants 
of the first section ; a short and round one 
in tliose of the second. The seeds are 
roundish, small, and attached alternately by 
a slender thread to both sutures, or joining 
of the valves. 
SIL 
SILK, the web or envelopment of tlid 
caterpillar, of a species of moth called the 
Phalena raori ; which being convertible to 
various purposes of utility and elegance, 
forms an important article in commerce, as 
the material of a valuable manufacture. The 
caterpillar, or silk-worm, when full grown, 
encloses itself in a loose web, in the midst 
of which it forms a much closer case or 
covering, of an oval form, and varying in 
colour from white to a deep orange, but 
usually of a bright yellow colour. In this 
case, or ball, the animal becomes a chry- 
salis, and remains enclosed about fifteen 
days ; w'heu having resumed active life, in 
the form of a moth, it makes a hole at one 
end of its prison and comes out. This, as 
it destroys the silk-ball, is prevented in 
those countries where silk is cultivated, by 
killing the chrysalides by means of heat. 
See Phalena. 
The silk-worm is supposed to be a native 
of China, at least the Chinese were the 
first nation in the world acquainted with 
the manufacture of silk. It was little known 
in Europe before the time of Augustus. 
Galen, who lived about the year 160, men- 
tions silk as in use no where but at Rome, 
and only among the rich. The Emperor 
Heliogabalus, who died in the year 220, is 
said to have been the first man that wore a 
holosericum, or dress, made wholly of silk y 
princes, as w'ell as subjects of the greatest 
quality, wearing only a stuff made of silk 
mixed with other materials. In the time 
of Aurelian, silk was sold in Rome for its 
weight in gold, and long continued to bear 
a great value, from the expense attending 
the mode in which it was procured. T'he 
only silk then known was that of China, 
which was brought from thence, in the raw 
state, to Berytus and Tyre, in Phoenicia, 
where it was manufactured ; but this branch 
of commerce being interrupted by the con- 
quests of the Scytliians, the Emperor Jus- 
tinian became desirous of establishing the 
culture of silk witliin his dominions; for 
which purpose he employed tw'o Monks, 
who had been in India, to procure the eggs 
of the insect from China. This was accom- 
plished about the year 555 ; the eggs were 
hatched at Constantinople, and the breed 
of the insect being carefully encouraged, 
raw silk was soon produced in abundance, 
which.was worked up into manfactures at 
Athens, Thebes, Corintli, and other places. 
It a))pears, however, tliat for many years 
after the establishment of the culture of 
silk in Greece, garments of this material 
