DEFINITION OF TERMS. 



169 



pose them, and separate the iodine. The 

 hydriodates of potash and soda are the 

 most interesting of their numhcr, hecause 

 they are the chief sources of iodine in 

 nature. The latter salt is prohalily the 

 one which affords the iodine obtained 

 from kelp; while it is believed, that it is 

 the hydriodate of potash which is most 

 generally found in mineral springs. 

 (Hence the necessity of adding sulphuric 

 acid to the residual liquor of the soap- 

 boiler, in order to procure the iodine, 

 which requires to be separated from its 

 combination with the alkali to which it is 

 united, in the condition of hydriodic acid ; 

 and peroxide of manganese is also added, 

 in order to facilitate the decomposition of 

 the hydriodic acid.) Iodine forms acids 

 also by uniting with oxj'gen and with 

 chlorine. When it is brought into con- 

 tact with protoxide of chlorine, imme- 

 diate action ensues; the chlorine of the 

 protoxide unites with one portion of io- 

 dine, and its oxygen with another, form- 

 ing two compounds — a volatile orange 

 colored matter, the chloriodic acid, and a 

 white solid substance, which is iodic acid. 

 Iodic acid acts powerfully on inflammable 

 substances; with charcoal, 'sulphur, sugar, 

 and similar combustibles, it forms mix- 

 tures which detonate when heated. It 

 enters into combination with metallic 

 oxides, giving rise to salts called iodales. 

 These compounds, like the chlorates, 

 yield pure oxygen by heat, and deflagrate 

 when thrown on burning charcoal: Iodic 

 acid is decomposed by sulphurous, phos- 

 phorous, and hydriodic acids, and by sul- 

 phuretted hydrogen. Iodine, in each 

 case, is set at liberty, and may be detect- 

 ed, as usual, in starch. Chloriodic acid, 

 which is also formed by simply immers- 

 ing dry iodine in chlorine gas, deliquesces 

 in the open air, and dissolves very freely 

 in water. Its solution is very sour to the 

 taste; and it reddens vegetable blues, but 

 afterwards destroys them. It does not 

 unite with alkaline bases; in which re- 

 spect it wants one of the characteristics 

 of an acid, and has hence been called by 

 Gay Lussac a chloride of iodine. Iodine 

 unites with nitrogen, forming a dark 

 powder, which is characterized chloride 

 of nitrogen, by its explosive property. 

 In order to form it, iodine is put into a 



solution of ammonia; the alkali is decom- 

 posed; its elements unite with different 

 portions of iodine, and thus cause the 

 formation of hydriodic acid and iodide of 

 nitrogen. Iodine forms with suljjhur a 

 feeble compound, of a grayish black co- 

 lor. With phosphorus, also, it combines 

 with great rapidity at common tempera- 

 tures, attended with the emergence of 

 heat. It manifests little disposition to 

 combine with metallic oxides; but it has 

 a strong attraction for the pure metals, 

 producing compounds which are called 

 iodurels, or iodides. The iodides of 

 lead, copper, bismuth, silver and mer- 

 cury, are insoluble in water, while the 

 iodides of the very oxidizable metals are 

 soluble in that liquid. If we mix a hy- 

 driodate with the metallic solutions, all 

 the metals which do not decompose water 

 will give precipitates, while those which 

 decompose that liquid will give none. 



Iodine, besides being employed for phi- 

 losophical illustrations, is used in the arts 

 for pigments, dj'es, and medicine. The 

 proto-ioduret of mercury is used in Eng- 

 land as a substitute for vermilion in the 

 preparation of paper-hangings ; and a 

 compound hydriodate of potassa G5, io- 

 date of potassa 2, and ioduret of mercury 

 33, is employed in printing calico. The 

 tincture of iodine, 48 grs. to 1 oz. of alco- 

 hol, is a powerful remedy in the goitre, 

 and other glandular diseases; but it is so 

 violent in its action on the system., as to 

 require great caution in its administra- 

 tion. The hydriodate of potash or of 

 soda is also applied to medical uses; and 

 it is inferred that the efficacy of many 

 mineral springs, in certain diseases, is 

 owing to the presence of one or the other 

 of* these salts. 



Iridium; the name of a metal disco- 

 vered in 1S03, by M. Tennant, in the 

 black residuum from the solution of the 

 ore of platinum. Its name was bestowed 

 in allusion to the rainbow, (iris.) in con- 

 sequence of the changeable color it pre- 

 sents while dissolving in muriatic acid. 

 Its color is white; it is brittle, and very 

 difficult of fusion; specific gravity, 18.68. 



Ipecacuanha, process to make Sirup of. 

 Take of Ipecac, bruised, - 1 part 

 Water, - - - 14 " 



