POI 
the flesh produces formidable effects. Many 
substances also act as poisons when applied 
either externally or internally, as arsenic, 
lead, &c. When a deleterious substance 
produces its effects, not only in mankind, 
but in all other animals, it is distinguished 
by the term common poison, as arsenic, 
caustic, alkali, &c. whilst that which is poi- 
sonous to man only, or to brute animals, 
and often to one genus only, is said to be 
a relative poison ; thus, aloes is said to be 
poisonous to dogs and wolves ; the phellan- 
drium aquaticum kills horses, whilst oxen 
devour it greedily and with impunity. It 
appears tlien, that substances act as poisons 
only in regard to their dose, the part of the 
body they are applied to, and the subject 
on which their powers are exerted. 
It is often of great importance to be able 
to discover, by certain chemical tests, cop- 
per and lead, particles of which frequently 
find their way into the stomach, either 
through inadvertencies, as by the employ- 
ment of certain kitchen utensils made of 
these materials, or by fraud, as when ace- 
tate of lead (sugar of lead) is made use of 
to revive wines that have grown sour by 
long keeping. If copper be suspected in 
any liquor, its presence may be ascertained 
by adding to it a solution of pure ammonia, 
which will strike a beautiful blue colour. 
If the solution be very dilute, it may be 
concentrated by evaporation, and if it con- 
tain a great excess of acid, as in the liquor 
of pickles, so much alkali must be added 
as will be sufficient to saturate the acid. 
Lead is affirmed by Dr. Lambe to exist 
in water that passes through leaden pipes, 
in such quantities as to be injurious to the 
human frame ; this has, however, been 
much doubted ; biit it is well known that 
petty dealers in wine have occasionally re- 
course to the acetate of lead to revive bad 
wines. Lead may be discovered in water 
by adding to a portion of it, about half its 
bulk of water impregnated with sulphu- 
retted hydrogen gas. If lead be present, 
if will be manifested by a dark brown, or 
blackish tinge. For discovering the pre- 
sence of lead in wine, a test is employed, 
called, from the name of the inventor, 
Hahnemann’s wine test. This is prepared by 
putting together into a small phial, sixteen 
grains of sulphuret of lime prepared in the 
dry way, and twenty grains of acidulous 
tartrite of potash (cream of tartar). The 
phial to be filled with water and well corked, 
and occasionally shaken for a few minutes. 
When the powdei* has subsided, decant the 
POL 
clear liquor, and preserve it, in a well stop- 
ped bottle for use. The test, when newly 
prepared, discovers lead by a dark coloured 
precipitate. Lead may be likewise disco- 
vered by adding to the wine a solution of 
the sulphate of soda, which will throw down 
a precipitate. If a large quantity of tlie 
acetate of lead has been taken, as by a 
child, inadvertently on account of its sac- 
charine taste ; an active emetic must first 
be given, and then the hydro sulphuret of 
potash, or of ammonia be taken, a solution 
of the common sulphuret will answer. 
POLAR, in general, something relating 
to the poles of the world, or poles of the 
artificial globes : thus we meet with polar 
circles, polar dial, polar projection, &c. 
POLARITY, the quality of a thing con- 
sidered as having poles; but chiefly used 
in speaking of the magnet. See Magne- 
tism, 
POLE, in astronomy, one of the extre- 
mities of the axis, on which the sphere re- 
volves. These two points, each ninety de- 
grees distant from the equinoctial or equa- 
tor, are by way of eminence called the 
poles of the world ; and the extremities of 
the axis of the artificial globes, correspond- 
ing to these points in the heavens, are 
termed the poles thereof. See Globe. 
Pole, in spherics, a point equally dis- 
tant from every part of the circumference 
of a great circle of the sphere, as the cen- 
tre is a plane figure ; or it is a point of 
ninety degrees distant from the plane of a 
circle, and in a line, called the axis, pass-/ 
ing perpendicularly through the centre. 
The zenith and nadir are the poles of the 
horizon ; and the ^oles of the equator are 
the same with those of the sphere. 
Poles of the ecliptic, are two points ou 
the surface of the sphere, 23° 30' distant 
from the poles of the world, and 90° distant 
from every part of the ecliptic. 
Poles, in magnetics, are two points of 
a loadstone, corresponding to the poles 
of the world ; the one pointing to the 
north, the other to the south. See Mag- 
netism. 
Pole, Perch, or Rod, in surveying, 
is a measure containing sixteen feet and "a 
half. 
Pole, or Polar star, is a star of the 
second magnitude, the last in the tail of 
ursa minor. Its longitude Mr. Flamsteed 
makes 24° 14' 41" ; its latitude, 66° 4' li". 
The nearness of this star to tlie pole, whence 
it happens that it never sets, renders it of 
vast service in navigation, &c. for deter- 
Ee 2 
