renheit, lost 37'5 parts by weight; of white oak, 
41 parts; of maple, 48. On an average, the 
quantity of water contained in green wood may 
be estimated at about 40 per cent.; and the 
quantity lost by drying or seasoning during eight 
or ten months, will not amount to more than 
about 25 per cent. The timber which is used for 
burning almost always contains about a quarter 
of its weight of moisture, which not only does 
not assist in producing heat, but actually absorbs 
a great deal, to effect conversion into vapour. 
The composition of woody matter may be repre- 
sented, on the average, as comprising 52 per 
cent. of carbon, and 48 per cent. of hydrogen and 
oxygen, in the proportions which form water ; so 
that the definitive products of its combustion 
ought to be carbonic acid and water. The heat 
disengaged during its combustion, necessarily 
proceeds from the union of its elements with the 
oxygen of the atmosphere; but, the hydrogen 
being already present with the proportion of 
oxygen required for its combustion, may be re- 
garded as already burned, and therefore the heat 
produced by the wood depends solely on the 
quantity of carbon which it contains. 
The calorific or heat-yielding power of any one 
kind of wood, used as fuel, suffers deduction cor- 
respondingly to the degree of moisture which is 
present in burning, and can be realized with 
little of this deduction only when the wood has 
been dried in stoves or otherwise rendered as 
dry‘as possible ; and the calorific power of differ- 
ent species, all in the same or similar states, is 
considerably controlled, not only by their pro- 
portional amount of carbon, but by their com- 
parative density, and by the peculiar character 
of their resinous, saline, and other specific se- 
cretions, and, probably on account of conflicting 
methods of testing or determining it, has been 
represented by some experimentalists as always 
essentially different, and by others as virtually 
or eventually uniform. Assuming that the quan- 
tity of heat be designated as unity which is re- 
quisite to raise one kilogramme of water one 
degree of the centigrade thermometer, or 2°2 lb. 
of water 1° 8 of Fahrenheit, the following table, 
by Rumford, shows the calorific power of one 
kilogramme of each of fourteen kinds of fire-wood, 
in the several conditions which it specifies; so 
that one kilogramme of dry lime-tree will raise 
3,460 kilogrammes of water one degree of the 
centigrade thermometer, or 2:2 lb. of it will raise 
7,612 lbs. of water 1° 8’ of Fahrenheit’s thermo- 
meter,—and so of the other instances. 
Kinds of wood. Units of heat 
evolved. 
Lime.tree dry . 3460 
The same thoroughly stove dried 3960 
Beech dry, four years seasoned 3375 
The same well dried in a stove . 3630 
Elm, from four to five years seasoned 3037 
Oak, fire- wood : 6 3550 
Ash, dry : 3075 
Wild cherry 33793 
TIMBER. 
Fir, dry 3037 
The same sell dried j ina eave 4 3750 
Poplar, seasoned 3450 
The same well dried in a a stove j 3712 
Hornbeam 3187 
Oak, dry . 3300 
From the experiments of Clement, it appears 
that the heating power of charcoal is equal to | 
7,050 units; and as dry wood contains 52 per 
cent. of charcoal, its heating power has been de- 
duced theoretically, as equal to 3,666. Mr. Mar- 
cus Bull in America, made a series of experiments 
to determine the relative quantities of heat given 
out by different. kinds of wood; and from these 
M. Peclet concludes that the same weight of dry 
wood of every kind has the same heating power, 
and that this for a kilogramme, or 22 lbs. avoird. 
of wood dried by artificial means, is equal to 
3,500 units, whilst the same quantity of the same 
wood which has been cut and seasoned during 
from 10 to 12 months, and which contain from 20 
to 25 per cent. of water, is no higher than about 260 
units. But though the same quantities of wood, 
brought to the same degree of dryness, appear to 
have the same absolute. calorific power, all are 
not alike adapted to the same purposes. Hard 
woods, for example, burn slowly, and give out 
less heat in a certain time than the less compact 
kinds of wood; and hence fir is preferred to oak 
in furnaces where the object is to obtain the 
most intense heats. 
The different species of trees may be distin- 
guished from one another, and are powerfully 
modified in their adaptations to the arts, by the 
size and arrangement of their cellular tissue. 
One series of white and shining lamine, called 
by botanists the medullary rays and by carpenters 
and other workers in wood the silver grain, ra- 
diates from the pith to the bark; and another 
series of minute cells, called by botanists the. 
concentric layers and by workers in wood the 
spurious grain, is disposed in circular lines or 
groups at successive distances around all the 
intermediate space between the pith and the 
bark; and both series, when examined in thin 
horizontal slices of the timber, through a com- 
mon four-power microscope, are seen to have a 
different arrangement, and to comprise different 
sizes of cells or grains, in the different species of 
wood. The characters of these series, in a few 
of the most common and diverse kinds of home- 
grown timber, may be advantageously studied 
by practical men; and shall here be copied, with 
slight condensation, from the Useful Knowledge 
Society’s Treatise on Planting, where illustrative 
diagrams of them may be seen.—The elm has the 
medullary rays, or silver grain, equal and not 
crowded. The concentric layers are composed of 
a series of cells of nearly unequal diameter, ar- 
ranged in an almost simple curved line. The 
spaces between the layers are furnished with 
cells of a smaller diameter, and rather thinly 
scattered over the surface—The oak has two 
