FOI 



POL 



poisons, the poison of hydrophobia, &c. 

 There are likewise substances which are 

 innoc< nt when taken into the stomach, but 

 which prove deleterious when taken into 

 the lungs, or when applied to an abraded 

 surface. Thus carbonic acid gas is con- 

 tinually swallowed with fermented liquors, 

 and thus the poison of the viper may be 

 swallowed with impunity; whilst inspir- 

 ing carbonic acid instantly destroys, and 

 the poison of the viper inserted into the 

 flesh produces formidable effects. Many 

 substances also act as poisons when ap- 

 plied 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 poisonous 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 poison- 

 ous to dogs and wolves ; the phellandri- 

 um aquaticum kills horses, whilst oxen 

 devour it greedily and with impunity. It 

 appears, then, that substances act as poi- 

 sons only in regard to their dose, the part 

 of the body they are applied to, and the 

 subject on which their powers are exert- 

 ed. 



It is often of great importance to be 

 able to discover, by certain chemical 

 tests, copper and lead, particles of which 

 frequently find their way into the stom- 

 ach, either through inadvertencies, as by 

 the employment of certain kitchen uten- 

 sils made of these materials, or by fraud, 

 as when acetate 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 so- 

 lution of pure ammonia, which will 

 strike a beautiful blue colour. If the so- 

 lution be very dilute, it may be concen- 

 trated by evaporation ; and if it contain 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. Lamb to exist 

 iu water that passes through leaden pipes, 

 in such quantities as to be injurious to 

 the human frame ; this has, however, 

 been much doubted ; but it is well known 

 that petty dealers in wine have occasion- 

 ally recourse to the acetate of lead to re- 

 vive bad wines. Lead may be discovered 

 in water, by adding to a portion of it 

 about half its bulk of water impregnated 

 with sulphuretted hydrogen gas. If lead 

 be present, it will be manifested by a dark 



brown, or blackish tinge. For discover- 

 ing the presence 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 twen- 

 ty grains of acidulous tartrite of potash 

 (cream of tartar). The phial to be filled 

 with water and well corked, and occa- 

 sionally shaken for a few minutes. When 

 the powder has subsided, decant the 

 clear liquor, and preserve it in a well 

 stopped bottle for use. The test, when 

 newly prepared, discovers lead by a dark 

 coloured precipitate. Lead may be like- 

 wise discovered by adding to the wine 

 a solution of the sulphate of soda, which 

 will throw down a precipitate. If a large 

 quantity of the acetate of lead has been 

 taken, as by a child, inadvertently, on ac- 

 count of its saccharine 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 sul- 

 phuret will answer. 



POLAR, in general, something relat- 

 ing to the poles of the world, or poles of 

 the artificial globes : thus we meet with 

 polar circles, polar dial, polar projec- 

 tion, &c. 



POLARITY, the quality of a thing 

 considered as having poles ; but chiefly 

 used in speaking of the magnet. See 

 MAGNETISM. 



POLE, in astronomy, one of the extre- 

 mities of the axis, on which the sphere 

 revolves. These two points, each nine- 

 ty degrees distant from the equinoctial 

 or equator, are by way of eminence call- 

 ed the poles of the world ; and the extre- 

 mities of the axis of the artificial globes, 

 corresponding to these points in the hea- 

 vens, are termed the poles thereof. See 

 GLOBE. 



POLE, in spherics, a point equally dis- 

 tant from every part of the circumfer- 

 ence of a great circle of the sphere, as 

 the centre 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, passing perpendicularly through the 

 centre. The zenith and nadir are the 

 poles of the horizon ; and the poles of the 

 equator are the same with those of the 

 sphere. 



POLES of the ecliptic, are two points on 

 the surface of the sphere, 23 3(X distant 

 from the poles of the world, and 90 dis- 

 tant from every part of the ecliptic. 



POLES, in magnetics, are two points of 

 a loadstone, corresponding to the poles 



