SILV ER. 
mums; but though two or three are somewhat 
ornamental, the majority have the look of mere 
weeds. They thrive in any common soil, and 
are propagated by division. 
SILVER. A metal which appears to have 
been known almost as early as gold, and, without 
doubt, for the same reason, because it occurs 
very frequently in a state of purity in the earth, 
and requires but an ordinary heat for its fusion. 
‘Mention is made of silver in the book of Job, 
which is considered the oldest of the books con- 
tained in the Old Testament. Pure silver is of 
a fine white colour, with a shade of yellow, with- 
out either taste or smell, and, in brilliancy, is 
inferior to none of the metallic bodies, if we ex- 
cept polished steel. It is softer than copper, but 
harder than gold. When melted, its specific gra- 
vity is 10'47; when hammered, 10°510. It is next 
in malleability to gold, having been beaten out 
into leaves only toooo00th of an inch in thickness. 
Its ductility is no less remarkable. It may be 
drawn out into a wire much finer than a human 
| hair; so fine, indeed, that a single grain of silver 
may be extended about 400 feet in length. Its 
tenacity is such, that a wire of silver 0:078 of an 
inch in diameter is capable of supporting a weight 
of 187:13 pounds avoirdupois without breaking. 
Silver melts when heated completely red-hot ; 
and, while in the melted state, its brilliancy is 
greatly augmented. If the heat be increased 
after the silver is melted, the liquid metal boils, 
and may be volatilized; but a very strong and 
long-continued heat is necessary. Gasto Claveas 
kept an ounce of silver melted in a glass-house 
furnace for two months, and found, by weighing 
it, that it had sustained a loss of one-twelfth of 
its weight. When heated upon charcoal under 
the flame of the compound blow-pipe, however, 
the silver is volatilized with rapidity, passing off 
in a visible smoke. When cooled slowly, its sur- 
face exhibits the appearance of crystals; and, if 
the liquid part of the metal be poured out as 
soon as the surface congeals, pretty large crystals 
of silver may be obtained. Silver is not oxidized 
by exposure to the air; it gradually, indeed, loses 
its lustre, and becomes tarnished; but this is 
owing to a different cause. Neither is it altered 
by being kept under water. But, if it be kept 
for a long. time melted in an open vessel, it 
gradually attracts oxygen from the atmosphere, 
and is converted into an oxide. 
SILVER FIR, —botanically Picea. A genus 
of trees of the pine division of the coniferous 
order. It was included first in the old genus 
pinus, and next in the later genus abies; and it 
possesses a somewhat close affinity to the present 
genus abies, or spruce fir, by its leaves being 
flattened and more or less pectinated and all 
turned toward one side, and by its seeds being 
irregularly shaped and more than half surrounded 
by the winged persistent pericarp. 
The common or pectinate silver fir, Picea 
pectinata—formerly called Pinus picea and Abies 
SILVER FIR. 223 
picea—is a native of the mountains of northern 
Asia and northern Continental Europe, and was 
introduced from Germany to Britain about the 
beginning of the 17th century. Its stem is tall; 
its form is pyramidal; its branches grow horizon- 
tally and in regular whorls; its bark is light- 
coloured and smooth; its leaves are pectinate, 
smooth, flattened, dark green, rather upwards of 
an inch in length, and rounded or very slightly 
indented at the point, and have one deep central 
channel on their upper side, and two silvery 
channels on their under side; its male catkins 
are stalked and shortly cylindrical; its cones are 
erect, cylindrical, from 4 to 6 inches long, fully 
one inch in diameter, and of a purplish colour in 
most varieties but white in some; its scales are 
rounded, very broad, incurved on the external 
edge, and toothed on the sides; and its seeds 
are triangular, somewhat wrinkled, fully one- 
third of an inch long, and nearly surrounded 
with a persistent, shining, brownish-purple peri- 
carp, and contain each 4 or 5 cotyledons. This 
tree naturally inhabits altitudes immediately 
below the zone of the wild pine or Pinus sylves- 
tris; and is exceedingly hardy as a plantation 
forest-tree in Britain; and will more or less 
grow in most situations and soils; yet it is very 
impatient of the sea-breeze, and makes most 
progress on good, rich, loamy, deep, rather moist 
land, in glens or at the base of hills or mountains, 
and does not thrive well or live long on soil 
which is either poor or shallow, or in a situation 
which is bleak or lofty. On its native grounds 
in Germany, it has always a perfectly straight 
stem, and attains a height of from 50 to 120 feet, 
and measures from 10 to 20 feet in girth at two 
yards from the ground, and is eventually cut 
from the Black Forest into valuable planks and 
sent in ‘floating villages’ down the Rhine to 
Holland; and in favourable situations, under 
proper management, in Britain, it is both a free- 
growing and a highly ornamental tree. A plant 
of it in Woburn Park, a few years ago, when 
about the age of 110 years, was 110 feet high, 
and measured 104 feet in girth at 4 feet from 
the ground, and contained 375 cubic feet of tim- 
ber. The common silver fir is of slower growth, 
in its earlier years, indeed, than some other 
hardy and favourite trees of its class; but, after 
about 15 years, it almost always takes the lead 
of at once the larch, the spruce, and the Scotch 
pine. It is, also, very subject, and fatally so, to 
the disease called the American blight, inflicted 
by a minute insect of the aphis kind; but it 
seems to contract this disease in consequence of 
stagnation and corruption of air, and may gen- 
erally be protected from it by means of wide 
enough planting, and of free and early pruning. 
The reputation it has acquired of being a deli- 
cate and comparatively tender tree, appears to 
have arisen entirely from inattention to the con- 
ditions of situation and soil and culture which 
are proper or essential to its habits. Its timber 
