216 SIEGESBECKIA. 
leaving only those species to be still called sidas 
which have one-seeded carpels. 
SIDERITIS. See Att-Hean (Crown’s). 
SIDEROXYLON. See Iron-Woop. 
SIDESADDLE-FLOWER. See Sarracenta. 
SIEGESBECKIA. A genus of curious and 
ornamental, exotic, annual plants, of the sun- 
flower division of the composite order. Six spe- 
cies, chiefly yellow- flowered and about 2 feet 
high, and all late in blooming, have been intro- 
duced to Britain from Mexico, Peru, Iberia, and 
India. 
SIEVE. An implement for separating smaller 
particles from larger ones. Sieves of many kinds 
are used in not a few departments of the useful 
arts, chiefly for separating finer grains or pow- 
ders from coarser ones; and sieves of several 
constructions and of different varieties are used 
on the farm for separating cereal grain and other 
seeds from dust and general impurities. Most 
sieves are textures of basket-work, wire, gut, or 
hair, stretched on a broad wooden hoop; but 
some consist of perforated and stretched skins or 
iron-plates ; and a few, for very fine work, particu- 
larly in the pharmaceutical processes of the drug- 
gist and the practical chemist, consist of lawn or 
other fine cloth stretched within high, thin, cir- 
cular frames. Barn sieves require to be of dif- 
ferent capacities for respectively beans, wheat, 
oats, rape-seed, and other produce. An excellent 
complex implement, called a seed-sifter, and well 
adapted for the separating and cleaning of rye- 
grass seeds, was invented about 12 years ago by 
Mr. Leckie of Haddington, and is modelled in 
the Museum of the Highland Society, and de- 
scribed and figured in the 12th volume of their 
Transactions. It contains three wire sieves, of 
different width of mesh, and is worked by means 
of a winch-handle and connecting machinery. 
“The rough seed is put into the upper sieve, 
which, by agitation, allows the ryegrass and 
smaller seeds to pass through, while husks and 
larger seeds are retained. The former are re- 
ceived upon the middle sieve and subjected to a 
second separation in which the fine ryegrass, 
dust, and small seeds only are passed through. 
These falling upon the lower or sloping sieve, 
are again separated, the dust and small seeds 
fall through this as waste, and the ryegrass seed 
in a clean state is discharged over the lower edge.” 
SIEVERSIA. A genus of ornamental, hardy, 
perennial- rooted, yellow-flowered, herbaceous 
plants, of the rosaceous order. Six or seven spe- 
cies, all but a few inches in height, and blooming 
from about midsummer till some time in autumn, 
have been introduced to Britain from North 
America, Continental Europe, and Siberia; and 
they, for the most part, love a soil of peaty loam, 
and are propagated by division. 
SIFTING. The separating of seeds from im- 
purities, or of smaller particles from larger, by 
means of implements. See the articles Srevz, 
Sorenn, and Turasaing-MacHine, 
SILICA. 
SILAUS. See Pepper Saxrrraaz, 
SILENE. See Carcurny. 
SILEX. See Sruica. 
SILICA. The oxide of silicium. 
great interest to the chemist, on account of its 
remarkable affinities and reactions,—to the geo- 
logist, on account of its vast predominance in 
many kinds of rock, or of its constituting a very 
large portion of the crust of the world,—to the 
mineralogist, on account of its being the chief 
ingredient in many gems and other rare and 
beautiful minerals,—to the phytologist, on ac- 
count of its forming an essential part of the food 
of plants,—and to the agriculturist, on account 
of its intimate connexion with the offices of soils 
and manures. 
Silicium or silicon is a simple body, belonging 
to the same group of elements as carbon and 
boron. It does not naturally exist in an uncom- 
bined state; and was first demonstrated to be 
a distinct body by Sir Humphrey Davy; and 
first obtained, in a pure separate state, in 1824, 
by Berzelius. It may be prepared in several 
ways,—but, most conveniently by decomposing 
highly dried double fluoride of silicium and pot- 
assium or sodium, and afterwards driving off 
some combined hydrogen and some adhering 
silica. It is a dark nut-brown substance, per- 
fectly destitute of metallic lustre, a non-conduc- 
tor of electricity, incombustible in air or in oxy- 
gen, infusible by the flame of the blow-pipe, and 
insoluble in sulphuric, nitric, muriatic, or hy- 
drofluoric acid, but vividly combustible in con- 
tact with carbonate of potash or soda, deflagra- 
ble in mixture with nitre under a high tempera- 
ture, and explosible by being dropped upon fused 
hydrate of potash, soda, or baryta. 
Silica or silex is one of the most abundant 
earthy substances in the world. It forms a great 
proportion of the primitive rocks; it is the chief 
ingredient in sandstones; it constitutes by far 
the main part of quartz rock, and is nearly iden- 
tical with flint; it forms from 50 to 70 per cent. 
of the total bulk of most barren soils, and from 
50 to 85 per cent. of the total bulk of most. fer- 
tile soils; and, under a great variety of slightly 
modifying circumstances, it constitutes almost 
the entire substance of calcedony, agate, jasper, 
rock crystal, and other analogous gems. It may 
be obtained in comparative purity by throwing 
red-hot pieces of transparent rock crystal into 
water, and afterwards pulverizing them; and, as 
thus obtained, it is a light, white, insipid, ino- 
dorous powder, rough and dry when rubbed be- 
tween the fingers, totally insoluble in water, 
fixed or quite infusible in the fire, but more 
readily fusible than lime or magnesia. before the 
oxyhydrogen blow-pipe. It is not acted on by 
any acid except the hydrofluoric; but it dissolves 
in solutions of the fixed alkalies, and combines 
with many of the metallic oxides. Silica itself, 
though incapable of acid reaction upon vegetable 
colours, claims, in reference to its behaviour with 
It possesses 
