TUR 
old balustrades, where its effect is far from 
being pleasing. The nature of the curve 
thus described, which we have called an el- 
lipsis vvill manifestly vary according to the 
law of the alternate motion in the mandrel. 
When the mandrel moves uniformly for- 
ward, the cut will be the common helix or 
screw ; and the motion is used to make 
screws, though not very frequently, because 
good turners can easily make them by a 
a notched cutting tool, called the screw. 
The act of turning is so extensively ap- 
plicable, that it would require a volume to 
describe its uses, and the methods of prac- 
tising it. Every round thing which is made 
by human hands may be referred to this art, 
as one of its products. The largest columns, 
the most ponderous artillery, and the mi- 
nutest pivots of watch-work, with all wheel- 
work, rotatory machines, vessels, &c. are 
worked in this method. 
TURNSOLE. See Litmus. 
TURPENTINE. See Resins. 
Turpentine, of which there are various 
kinds, are all products of some of the 
species of the pinns. From this genus are 
obtained not only turpentine, but resin, 
pitch, tar, &c. which are employed so ex- 
tensively in ship-building, and in the rigging 
also : likewise in varnishes. 
There are diree varieties of pine turpen- 
tine, commonly known pnder that name in 
Europe: namely, 1. The common turpen- 
tine, obtained chiefly from the pinus sylves- 
tris (Scotch fir). 2 . The Strasburgh tur- 
pentine, yielded by the pinus pieca (silver 
fir). And, 3. The Venice turpentine, pro- 
cured from the pinus larix (larch). Of the 
three first mentioned turpentines, the Ve- 
nice is the thinnest and most aromatic; the 
Strasburgh the next in these qualities, and 
the common is the firmest and coarsest. 
The two former are often adulterated by a 
mixture of the common turpentine and oil of 
turpentine, and it is to be observed, that the 
terms Venice and Strasburgh turpentine are 
not now appropriate, as they arg procured 
from various countries. 
Common turpentine is obtained largely 
in the pine forests in the south of France, in 
Switierland, in the countries on the north 
of the Pyrenees, in Germany, and in many 
of the southern States of North America. 
The greater part of what is consumed in 
this country is imported from North Ame- 
rica. The method of obtaining it is by 
making a series of incisions through the 
bark of the tree, from which the turpentine 
exudes, and falls down into htfles, or other 
receptacles at the foot. 
TUR 
Tlie process is described very accurately 
by Duhamel and others, as practised in 
the south of France. The fir is generally 
allowed to remain untouched till it is thirty 
or forty years old. When it is to be work- 
ed, which is early in the spring, a small hole 
is first made in the ground at the foot of the 
tree, the earth of which is well rammed, 
and serves as a receptacle for the juice. 
The coarse bark is then stripped off from 
the tree, a little above the hole, down to 
the smooth inner bark, after which a por- 
tion of the inner bark, together with a little 
of the wood, is cut out with a very sharp 
tool, so that there may be a wound in the 
tree about three inches square, and an inch 
deep. Immediately afterwards the turpen- 
tine begins to exude in very transparent 
drops, which escape chiefly from the wood 
immediately under the inner bark. Tlie 
hotter the weather is the greater is the 
supply of resin, and to facilitate the sup- 
ply the incisions are enlarged every three 
or four days, by cutting off thin slices, 
till at the end of the year it is about a foot 
and a half wide, and two or three inches 
deep. The whole time during which the 
turpentine flows is from the end of February 
to October. In the winter it entirely ceases, 
but in the ensuing spring a fiesh incision is 
begun a little above the former, and manag- 
ed in the same manner. This practice is 
continued annually for about twelve or fif- 
teen years in some parts, and in others a 
shorter time, on the same side of the tree, 
till the later incisions are so high as to be 
out of reach without the assistance of steps ; 
after which the contrary side of the tree is 
begun upon, and worked in a similar man- 
ner for as many years, during which time 
the first incisions are grown up, and are fit 
to be cut afresh. In this way, a healthy 
tree, in a favourable soil, may be made to 
yield from six to twelve, or more, pounds 
of turpentine anntially, sometimes for a cen- 
tury ; and even the timber is not soon in- 
jured by this constant drain. The flow of 
turpentine discontinues altogether about 
October, and the liquid resin collected 
during the year, from each tree, is put to- 
gether for further purification. But a con- 
siderable quantity of the resin has concreted 
during that time around the incision, par- 
ticularly as the heat declines; and in the 
winter, when it has hardened considerably, 
it is scraped off, and forms what is techni- 
cally called barras, or in some provinces 
galipot, which differs from the more liquid 
turpentine in consistence, and probably 
contains a less proportion of essential oil, 
