or circumference beween the butt-end and the 
top-end, to square the fourth of this mean, to 
multiply the product by the length, and to de- 
duct an allowance for the bark. But this method 
does not bring out a result sufficiently near the 
truth, in cases where the timber is of any con- 
siderable value; and a much better one would 
be to multiply the square of the circumference 
by the length, and to multiply the product by 
07958. The allowance for bark ought to vary 
widely in trees of different species, and consider- 
ably in different individuals, particularly in the 
young and the old, of the same species. In 
England, the customary allowance is one inch 
for every foot of the quarter of the mean circum- 
ference of rough-barked or thick-barked species, 
such as the oak and elm, and half an inch for 
every foot of smooth-barked or thin-barked spe- 
cies, such as ash; and in Scotland, it is two 
inches for every circumference of from 12 to 24 
inches, three inches for every circumference of 
from 24 to 36 inches, four inches for every cir- 
cumference of from 36 to 48 inches, five inches 
for every circumference of from 48 to 72 inches, 
and six inches for every circumference of upwards 
of 72 inches. The contents of any hewn piece of 
timber, whose bases are parallel to each other, 
and whose greatest and least thicknesses are at 
the ends, may be readily and accurately deter- 
mined by finding the areas of the two bases and 
the area of a section parallel to and equidistant 
from the bases, multiplying this last area by 4, 
adding to the product the other two areas, and 
multiplying the same by one-sixth of the length. 
The measuring of sawn and worked timber in 
the several departments of carpentry, is noticed 
in the article Carpenter's Work. 
Timber is generally hewn into logs, and sawn 
into planks and deals, and sold by the load. See 
the articles Log and Prank. A load of unhewed 
timber comprises 40 feet, a load of squared tim- 
ber 50 feet, a load of one-inch plank 600 square 
feet, a load of 14-inch plank 400 square feet, a 
load of 2-inch plank 300 square feet, a load of 
23-inch plank 240 square feet, a load of 3-inch 
plank 200 square feet, a load of 33-inch plank 
170 square feet, and a load of 4-inch plank 150 
square feet. 
TIMBER TREE. 
PLANTATION, 
TIMOTHY-GRASS. See Puievm. 
TIN. One of the metals. It does not occur 
See Trezr, Timper, and 
| in many districts of the globe, but is very 
abundant in a few,—particularly in Cornwall, in 
part of Bohemia, in Galicia, and in Malacca. 
The tin mines of Cornwall have been worked 
from a very remote period, and have sent their 
produce to very distant parts of the world, and 
make a conspicuous figure in the constant indus- 
try of the south-east of England. The tin of 
these mines is both extracted from veins in vari- 
ous kinds of matrices, and found in the form of 
rounded grains among beds of rolled materials 
which have been deposited by running water; 
and it occurs both metallically in combination 
with sulphur and copper under the form of tin 
@. 
pyrites, and oxidizedly in combination with oxide 
of iron and silex under the forms of tin-stone and 
wood-tin. The granular ore in the deposits of 
running water is commonly called stream tin, 
and contains a very pure oxide, and yields the 
purest kinds of the tin of commerce; and the 
veined ore is by far the most abundant, and has 
a wide diversity of form and character and value, 
and requires to be subjected to an operose pro- 
cess of metallurgy. The ore, when necessary, is 
blasted with gunpowder; and, when raised out 
of the mine, it is divided into as many shares or 
‘dolls’ as there are proprietors and adventurers ; 
and that of each mine is distributed on the ad- 
jacent fields, The ore is generally pounded or 
stamped on the spot, in the pounding-mill; if 
slimy, it is thrown into a pot, called a buddle, to 
render the pounding more free, without choking 
the grates; and if free from slime, it is shovelled 
into a kind of sloping canal of timber, called ‘the 
pass, whence it slides by its own weight, and 
the assistance of a small stream of water, into 
the box where the ‘lifters’ work. The lifters 
are raised by a water-wheel, and are armed at 
the bottom with large masses of iron of about 14 
ewt., which pound the ore small enough to allow 
of its passing through the holes of an iron grate, 
fixed in one end of the box. It is kept con- 
stantly wet by a rill to assist its attrition; and 
it is carried by a small gutter into the ‘ fore-pit,’ 
where it makes its first settlement; and the 
lighter particles run forward with the water into 
‘the middle-pit,’ and thence into the third, where 
what is called the slime settles. From these pits 
the ore is carried to ‘the keeve,’ where it is tho- 
roughly cleansed from its filth, and rendered fit 
for smelting. It is then carried to works con- 
structed for this operation, and delivered to the 
smelter, and here it is assayed, to determine its 
quality, and then fined, and run into moulds of 
an oblong form; and when cooled, these masses 
are taken out of the moulds, and under the 
name of blocks of tin are carried to one of the 
coinage towns to be coined. A comparatively 
pure tin—though not so pure as that obtained 
from the stream ore—is prepared by heating a 
smelted block from the common ore to very near 
the point of fusion, and allowing only the most 
fusible portions of it to melt out,—these being 
much purer than the less fusible portions. The 
usual impurities are iron, copper, arsenic, and 
sulphur; and the worst of these can be dissipated 
by means of roasting in an intense heat. 
Tin has a white colour, and a lustre similar to 
that of silver; it slowly loses its lustre by ex- 
posure to the air, but does not oxidize even un- 
der the combined agency of air and moisture; it 
has a very slight and somewhat disagreeable 
taste, and emits a peculiar odour when rubbed; 
it is soft and inelastic, can be easily cut with a 
AG1. 
