34 DESCRIPTIVE LIST OF THE PRINCIPAL 
from oak, in having no large transverse septa—though in every other respect 
the two woods are remarkably similar in texture and color. Unlike most other 
woods chesnut, when strained to its breaking pitch, gives way without any warning, 
more in the manner of metals than woods. 
Outside wood contains 4.56 per cent. of potash; inside wood 2.73 per cent. 
Specific gravity 0.5; weight of cubic foot 32 lbs. 
Value for heating purposes 52. 
15. Doawoov. Cornus florida. 
Nat. Ord. Cornacee. 
Called also Cornel—the name being derived from the Latin cornu, a horn, 
alluding to the hardness of the wood. Occurs in rocky woods, but rarely in our 
latitudes, more common southwards. Tree 12 to 30 feet high, flowers in May and 
June, very showy in flower, and scareely less so in fruit. Wood very hard, but 
at the same time tough, and is used for making mallets (being also very heavy). 
It seems well adapted for many purposes for which boxwood is employed, as seales 
and measuring rules, paper cutters, de. 
It isso remarkably free from silex that splinters of the wood are used by 
watchmakers for cleaning out the pivot holes of watches, and by the optician for 
removing the dust from small deep-seated lenses. The trunk is covered with a 
peculiarly rough but soft bark, which is extremely bitter, and is used in medicine 
as a tonic. 
Specific gravity 0.78; weight of cubic foot 50 Ibs. 
Value for heating purposes 75. 
16. Rook Etm. Ulmus racemosa. 
Nat. Ord. Ulmacee. 
A small or middle-sized tree, with tough reddish wood and a very mucilaginous 
inner bark; flowers in March and April. Rare and valuable, being held in high 
esteem for piles. It is not liable to split, and bears the driving of nails and bolts 
better than auy other timber, and is exceedingly durable when constantly wet; it 
is therefore much used for the keels of vessels, and for wet foundations, water- 
works, piles, pumps, and boards for coffins ; from its toughness, elm is selected for 
naves of wheels, shells for tackie-blocks andésometimes for gunwales of ships, and 
also for many purposes of common turnery, as it bears very rough usage without 
splitting. 
There are four species of elms indigenous to North America. 
Specific gravity 0.59; weight of cubic foot 36.75 lbs. 
17. Swame Erm. Ulmus americana. 
Nat. Ord. Ulmacee. 
Grows in moist woods, especially along rivers in rich soil, and is very common. 
A large and well known ornamentul tree, with spreading branches and drooping 
branchlets ; flowers in April. Timber by no means so valuable as that of rock 
elm, though partaking of its characteristics. It is much sought on account of the 
mucilage of the inner bark. 
The timber of the elm is perfectly durable when kept dry, but not when ex- 
