URFINITIOX OF TERMS. 



167 



many right angles as the figure hath 

 sides, excepting or subtracting four. 



Intersection, in the mathematics, sig- 

 nifies the cutting of one line or plane by 

 another: thus we say that the mutual in- 

 tersection of two planes is a right line. 



Invention, in science, is distinguished 

 from discoveri/, as implying more crea- 

 tive combining power, and generally sig- 

 nifies the application of a discovery to a 

 certain purpose. 



Involution, in mathematics, the rais- 

 ing of a quantity from its root to any 

 power assigned. Thus 2 X 2 X = 8. 

 Here S, the third power of 2, is found by 

 involution. By continuing the process, 

 we can obtain any power of 2, and so 

 with other numbers. 



Iodine, the name of an undecompound- 

 ed principle or element in chemistry. It 

 had escaped the observation of chemists 

 until 1812, when a manufacturer of salt- 

 petre at Paris detected it in the ashes of 

 sea-weeds, in the following manner. In 

 evaporating the ley from these ashes, to 

 procure the carbonate of soda which they 

 contain, he noticed that the metallic ves- 

 sels with which he operated were power- 

 fully corroded, and that the corrosion was 

 increased as the liquor became more con- 

 centrated. Having at hand, one day, a 

 bottle of sulphuric acid, he added some 

 of it to a portion of the mother-water, 

 and was surprised to see a rich violet 

 vapor disengaged ; this vapor was the 

 iodine. Heat ond'e communicated the ob- 

 servation to M. Clement Desormes, who 

 sat about collecting some of the vapor, 

 and after examining its leading proper- 

 ties, announced it as a new body. Its 

 real nature was soon after unfolded 

 through the accurate researches of Gay 

 Lussac and Sir H. Davy. Its history 

 proved singularly interesting in modify- 

 ing the then prevailing theory of che- 

 mistry. Sir H. Davy had a few years 

 previously promulgated the new theory 

 of chlorine, which was still received with 

 suspicion among chemists. The strong 

 analogies, however, between this sub- 

 stance and chlorine, in their relations to 

 combustibles, both bodies forming com- 

 pounds by uniting with them, similar to 

 acids containing oxygen or oxides, were 

 conceived to give great weight to the 



views of Sir H. Davy, and operated com- 

 pletely to overthrow the erroneous hy- 

 pothesis of oxygenation invented by La- 

 voisier. Its investigation, therefore, may 

 be said to have formed a new era in 

 chemistry. The physical properties of 

 iodine are as follows; it is a soft, friable, 

 opaque solid, cf a blueish black color, 

 with a metallic lustre, usually in scales, 

 but sometimes in distinct crystals of the 

 form of rhomboids, or rhomboidal tables, 

 referable to an octahedron, with a rhom- 

 bic base as their primary form; its spe- 

 cific gravity is 4.946. It ])Ossesses an 

 odor somewhat analogous to that of chlo- 

 rine. It is a non-conductor of electrici- 

 ty, and possesses in an eminent degree 

 the electrical properties of oxygen and 

 chlorine. 



Iodine enters into fusion at 225° Fahr., 

 and boils at 347°; but when moisture is 

 present, it sublimes rapidly at a tempera- 

 ture considerabl}' below 212°, and gives 

 rise to a dense vapor of the usual violet 

 hue. It is scarcely soluble in water, but 

 is readily taken up by alcohol and ether, 

 to which it imparts a reddish brown co- 

 lor. It extinguishes vegetable colors, but 

 with less energy than chlorine. It is not 

 inflammable. Its range of affinitj^ for 

 other bodies is very extensive; the most 

 important compounds it forms with these 

 we shall describe after alluding to its na- 

 tural state and preparation. It exists 

 most abundantly in the various species of 

 fucus, which form the greatest part of the 

 sea-weeds of our coast; it also occurs in 

 the sponge, and in the coverings of many 

 molluscous animals, and has been found 

 in a great nun^ber of mineral waters, as 

 those of Salz in Piedmont, Saratoga in 

 New York, &c., and more recently has 

 been detected in some silver ores from 

 Mexico, and in an ore of zinc from Up- 

 per Silesia. But it is from the incinera- 

 ted sea-weed, or kelp, that the iodine, in 

 large quantities, is obtained. As the soap 

 manufacturers are in the habit of obtain- 

 ing their soda from kelp, iodine may be 

 procured, very economically, from the 

 residuums of their operations, according 

 to the process invented by Di-. Ure, which 

 is as follows. 



The brown iodic liquor of the soap- 

 boiler, or the solution of kelp from which 



