ion. 



IODINK. 



The mate difficulty mint exist in every method, as matters now stand- 

 in the meanwhile, we think the discoverer of the process, which is 

 now beginning to take it* proper place, deserves attention to his 

 request when he says, speaking of the antagonist claims which had 

 started up " All I ask of them (mathematicians) in recompense for 

 the facilities consigned to their use in the non-figurate method, is to 

 bear in mind that I alone am the author of it." And we have no 

 doubt whatever, and are willing to stake our credit upon it, that when 

 the inertia of the higher mathematicians in matters of computation is 

 overcome, and when the mode of solving equations has reached the 

 schoolboys, u it is rapidly doing, the name of Homer will be one of 

 the household words of pure arithmetic, and himself looked upon as 

 one of the greatest of its modern benefactor*. Justice requires that 

 his name should remain attached to his process. 



IOD or IODO. A prefix used in chemistry to signify that the body 

 to the name of which it ie attached contains iodine substituted for 

 some other element. Such compounds will generally be found described 

 under the name of the body to which this prefix is attached. 



IODAL (C.HI.OJ Hydride of tri-iodacetyl. A body analogous to 

 CHLORAL, said to be produced by mixing alcohol with nitric acid and 

 then adding iodine. Its existence has not been satisfactorily estab- 

 \ ' \ 



IODAXILINE (C..HJN). A derivative of aniline. [ANILINE.] 



IODHYDRIX (C./H.^O.). A liquid compound produced by the 

 action of hydriodic acid upon glycerin. [GLICCKIX.] 



IODICACID. [IODINE.] 



IODIDES. [IODINE. Hydrogen and Iodine.} 



IODINE (I), a non-metallic, elementary, or simple solid body, dis- 

 covered by M. Courtois, of Paris, in 1812. Ita peculiar properties 

 were however first ascertained by Gay-Lussac and Davy. Iodine exists 

 in the water of the ocean and mineral springs, probably combined with 

 sodium, or calcium, or magnesium ; also in marine molluscous niml 

 and sea-weeds; and has been met with in combination with silver. 

 Iodine is principally obtained from kelp, or sea-weed which has been 

 burnt for the purpose of obtaining alkali from it. When the alkaline 

 and other salts hare been separated from this ah, the residual solution 

 is treated with sulphuric acid and binoxide of manganese, by which the 

 iodine is set free, the decomposition being analogous to that by which 

 chlorine is obtained by the aame agency from common salt. 



Mai + HnO, + ISO, 



Iodide of Binoxide of Sulphuric 

 odium, manganese, acid. 



NaO, SO. + MnO.SO, + I 



Sulphate of 



- 



Sulphate of Iodine, 

 manganese. 



The process is conducted in leaden retorts of cylindrical form, and 

 heated on a sand-bath to a temperature not exceeding 212 Fohr.,a 

 higher heat than this causing loss from the formation of chloride of 

 iodine. At this temperature the iodine slowly vaporises, and passing 

 off through the neck of the retort is condensed to the solid form in a 

 series of flasks connected together by the neck of each passing through 

 a hole in the bottom of the one preceding it. 



Iodine is a soft opaque solid, of a bluish-block colour and metallic 

 lustre. The primary form of the crystal is an acute rhombic octohe- 

 dron. The crystals are usually fiat. According to Gay-Lussac, its 

 specific gravity is 4'947. When moderately heated, it rises in vapour 

 of a violet colour, and hence its name from the Greek (10(07)1, " vjuli-t- 

 coloured "). On cooling, it again crystallises unchanged, nor is it altered 

 by being subjected to very high temperatures; it has resisted all 

 attempts to decompose it. Iodine has a strong disagreeable odour and 

 taste, somewhat resembling bromine and chlorine ; it stains the skin of 

 a brownish colour, but not permanently. It is readily dissolved by 

 alcohol, and the solution is of a reddish-brown colour ; so little is 

 taken up by water that a pound of that liquid will not dissolve more 

 than a grain of iodine. It is very poisonous. Ita characteristic pro- 

 perty is that of giving an intense blue colour when added to a solution 

 of starch. It unites with metals to form compounds, termed iodides ; 

 these are all decomposed by chlorine, or even bromine, iodine being 

 liberated. They will be found described under the names of the 

 respective metals. Iodine, like chlorine and bromine, forms acids both 

 with hydrogen and oxygen. 



The equivalent of iodine is 126'8 ; its combining volume, 2 ; and the 

 specific gravity of iU vapour, 6716. 



Oxygen and Iodine combine to form probably four compounds. 

 When the vapour of iodine and oxygen gas are mixed at rather a 

 high temperature, the violet tint of the iodine disappears, and a yellow 

 wift substance is formed, which is regarded by Kementiui as oxide of 

 iodine ; if this be subjected to the action of more oxygen gas, it a 

 converted into a yellow liquid, which the same chemist supposes to be 

 iod<mt acid ; but the composition and properties of these compounds 

 have not been accurately determined. 



/orfi> A riil ( 10. i. Tlii rrmi|ximid was first obtained by Davy by the 



action of iodine upon what he called euchlorine gas. A better process 



however consist* in heating the iodine in the strongest nitric acid. For 



this purpose the acid should be introduced with about a fifth ! itx 



weight of imliiK- into a capacious retort, and kept boiling for 12 hours; 



I HIP which riies and condense* on the Hides of the retort is to be 



1 to the acid either by a glass tube or by agitation ; when the 



iodine disappears, the excess of nitric acid is to be got rid of by evapo- 



ration, lodic acid is a white semi-transparent solid substance, which 

 may, however, be obtained in crystals containing one equivalent of 

 water (HO, IO,). It is inodorous, but has an astringent sour taste. 

 It is so dense as to sink in sulphuric acid, and it deliquesces in a moist 

 atmosphere. It is very soluble in water ; the solution reddens vegetable 

 blue colours ; it detonates when mixed and heated with charcoal, sugar, 

 and sulphur. When crystals of iodic acid are heated to 360 Fanr., 

 they become anhydrous, and at about 700 are decomposed into iodine 

 and oxygen. Iodic acid combines with metallic oxides to form salts, 

 which are termed iodatet, containing one, two. or three atoms . 

 to one of base, and these, like the chlorates, yield oxygen when heated ; 

 an iodide remaining. 



Periodic Acid (!&,). When chlorine is added to saturation to a 

 solution of iodate of soda with excess of the alkali and couo-ntr.it. -,l by 

 evaporation, a sparingly soluble white salt is obtained, which is fter- 

 iodate ofioda ; when this is dissolved in dilute nitric acid and mixed 

 with nitrate of silver, a yellow precipitate falls, which, dissolved in hot 

 nitric acid and evaporated, yields orange-coloured crystals of periodate 

 of silver ; these are decomposed by cold water, and an aqueous solution 

 of pure periodic acid 'formed; this by cautious evaporation yields 

 crystals, containing five equivalents of water of hydration. When 

 heated to 212, they ore resolved into oxygen and iodic acid. 



Nitrogen and Iodine appear to form three distinct compounds, con- 

 taining respectively NH,I, NHI,, and NI V derived no doubt from 

 ammonia (NH^) by the substitution of hydrogen by iodine, thus : 



" 

 N { II 



I H 



N ? II 

 II 



(I 

 ' 

 II 



"i: 



Iodide of nitrogen, or probably, a mixture of the iodides, is best 

 prepared by dissolving iodine in aqua regia, and pouring the mixture 

 into strong solution of ammonia; it then precipitates as a puce- 

 coloured powder ; or iodine may simply be powdered and digested at 

 once in the ammonia, when an iodide remains insoluble in the state of a 

 dark brown powder. This compound is very explosive, especially 

 when dry : the best method of exhibiting its power is that of allowing 

 it to dry in small portions on bibulous paper, and then simply letting 

 it fall on the ground or merely touching it, when it detonates with a 

 sharp noise, heat and light being emitted, and the vapour of iodine and 

 nitrogen gas evolved. It is not dangerously explosive in quantities of 

 3 or 4 grains. 



Hydrogen and Iodine form hydriodic acid (HI), which may be pre- 

 pared by the direct combination of its elements. When a mixture of 

 iodine in vapour and hydrogen gas is passed through a red-hot porce- 

 lain tube, they combine to form this acid. It is however much more 

 conveniently formed by heating in a retort ten parts of iodide of potas- 

 sium, five of water, and twenty of iodine, and cautiously dropping in 

 one part of phosphorus cut into small pieces; hydriodic acid then passes 

 over in the state of a colourless gas, and may be collected by displace- 

 ment in dry bottles. This acid has a sour taste, reddens vegetable 

 blues, and when mixed with atmospheric air forms dense white fumes 

 with its moisture : its odour resembles that of hydrochloric acid gas. 

 It is soluble in water. The salts which it forms are termed iodidet. 

 When it is acted upon by metals, hydrogen is evolved, ami when l>y 

 metallic oxides, water is formed, and in both cases iodides result. 



It is decomposed by oxygen when they are heated together ; water 

 is formed, and iodine evolved. It is also immediately decomposed by 

 chlorine, which unites with its hydrogen to form hydrochloric acid, 

 and iodine is set free. 



Chlorine and Iodine form two chlorides. The protocltloride (IC1) 

 may be obtained by passing a current of chlorine gas into water in 

 which iodine is suspended. A deep reddfoli solution is formed that 

 yields irritating fumes possessing the smell of both the elements : it 

 first reddens and then bleaches litmus paper. The ttrcMoridr (K'l ^ 

 is best formed by acting upon iodine with excess of dry chlorine gas. 

 It forms fine ruby-red crystals. 



line and Iodine form compounds corresponding with tlio 

 chlorides. 



Kul/iliiir and Iodine. Four parts of iodine and one of sulphur 

 bine on the application of gentle heat, and yield a product of dark 

 colour and radiated crystalline structure. It is easily decomposed by 

 In at. 



Phoiphona and Iodine unite in twc^ proportions. The biniodide 

 (PL) is formed by dissolving one equivalent of phosphorus in bisul- 

 phide of carbon, and adding two equivalents of iodine. On cooling the 

 mixture to a very low temperature, acicular crystals of orange colour 

 are deposited. The tcriodide (PI,) is produced in a similar manner to 

 the last, three equivalents of iodine being used instead of two. It 

 forms dark red tabular crystals. 



Carbon and Iodine appear to form no true compound. 



IODINK. iMiilii-iinil l'ri>irtie*of. Iodine, though only obtained in 

 an isolated state in the year 1811, has been long employed as the 

 efficient principle of other preparations and therapeutic agents, namely, 

 burnt sponge and certain mineral waters. [WATER, subsect. Mineral, in 

 NAT. HIST. Div.] It is only since it has been procured OK a distinct prin- 

 ciple t hat its action has been ascertained with precision. In the present 

 ilny it is administered rather in some artificial compound than as pure 

 iodine, owing to its very sparing solubility in water. Iodine in substance, 



