196 



I O D I N E. 



1 inline. 



Oxiodate of 

 ammonia. 



Oxiodates 



uf barytcs. 



Action of 

 iodine on 

 vegetable 

 substances. 



Hydriodic 

 ether. 



rating oxiodic acid with ammonia, or by saturating with 

 it a solution of chlorine and iodine, (the chloruret of 

 iodine of Gay- Lussac. ) This oxiodate assumes the form 

 of small granular crystals. On a hot body it detonates 

 with a hissing noise, a weak violet light, and the dis- 

 engagement of vapours of iodine. When decomposed 

 by heat, it gives out a mixture of oxygen and azote. It 

 is composed of 



Oxiodic acid 100.00 



Ammonia lO.p^. 



Oxiodate of barytes is easily obtained by double af- 

 finities, or by putting iodine into barytes water. It 

 precipitates in the form of a powder, which may be 

 purified by repeated washing. While drying it con- 

 cretes into lumps, and becomes mealy. It retains wa- 

 ter in composition, which it gives out at a temperature 

 of 212", before being decomposed by heat. It is com- 

 posed of 



Oxiodic acid . . 100 



Barytes 46.3-M). 



On hoat coals it does not deflagrate, but only gives 

 out a weak intermitting light. It is infusible, and only 

 a small quantity of the salt comes in contact with the 

 fuel, so that the oxygen which is disengaged contri- 

 butes very little to its combustion. 



The oxiodate of strontites has similar properties. 



The oxiodate of lime is generally pulverulent, but 

 may be crystallized in the muriate or the hydriodate of 

 lime, which augment its solubility, and it then as- 

 sumes the form of small quadrangular prisms. It holds 

 about 3 per cent, of water in combination. 



The other oxiodates may be obtained by double de- 

 compositions. Nitrate of silver gives with the oxio- 

 date of potass a white precipitate, which is the oxio- 

 date of silver, and is very soluble in ammonia. 



The oxiodates do not, like the hydriodates, absorb io- 

 dine to form iodureted salts. Their solutions absorb 

 no more of this substance than is done by pure water. 



Iodine gives a blue colour to starch by combination ; 

 and this is done with such facility, that starch is one 

 of the most delicate tests of this substance. It does not, 

 however, detect it in the state of acid, unless the iodine 

 is previously evolved by some other acid substance. 



On mixing two parts in volume of alcohol with colour- 

 ed hydriodic acid of the specific gravity of 1 .7, and dis- 

 tilling the mixture in a water bath, an alcoholic liquor is 

 produced, colourless and limpid, which, when mixed 

 with water, becomes muddy, and lets fall in small glo- 

 bules a liquid, at first milky, which gradually becomes 

 transparent. This is hydriodic ether. What remains 

 in the retort is hydriodic acid, very dark coloured, from 

 holding in solution all the iodine which had coloured 

 the original quantity. Hydriodic ether, after being 

 washed two or three times with water, (in which it 

 has very little solubility,) is in a pure state. It has a 

 .strong and peculiar odour, though analogous to that of 

 the other ethers. After some days it acquires a red 

 colour, from the evolution of a little iodine, which, 

 however, does not afterwards increase. This colour 

 may be removed by the addition of a little potass or 

 mercury, which combine with the iodine. The speci- 

 fic gravity of this ether, at 7'2i, is 1.9206. It boils at 

 148.1. It is not inflammable a circumstance very sin- 

 gular in an ether. It only exhales purple vapours when 

 thrown on burning coals. Potassium may be preser- 

 ved in it without alteration. Concentrated sulphuric 

 acid renders it brown. When passed through a red-hot 

 tube, it is speedily decomposed, giving an inflammable 

 carbureted gas, very brown hydriodic acid, and a little 

 charcoal. 



The concurrence of properties which we find in io- Iodine. 

 dine, and its various states of chemical combination, ^""^VT"^ 

 is curious and singular. '' In its specific gravity," says A , n . al r? ies 

 Sir H. Davy, who considers it as an x undecompound- vithothcr 

 ed body, " in lustre, the high number in which it en- substances, 

 ters into combination, and in colour, it resembles the 

 metals. But in all its chemical agencies it is more ana- 

 logous to oxygen and chlorine : it is a non-conductor of 

 electricity, and possesses, like these bodies, the nega- 

 tive electrical energy with respect to metals, inflamma- 

 ble and alkaline substances ; and hence, when combi- 

 ned with these substances in aqueous solution, and 

 electrized in the voltaic circuit, it separates at the posi- 

 tive surface : but it has a positive energy v with respect 

 to chlorine ; for, when united to this substance to form 

 a compound acid, it separates from it at the negative 

 surface. It has a stronger attraction for most of the 

 metals than oxygen, but oxygen expels it from phos- 

 phorus and sulphur. Under a red heat oxygen con- 

 verts the ioduret of phosphorus into phosphoric acid, 

 and evolves the iodine. Its saturating powers seem 

 to be greater than those of oxygen, and less than those 

 of chlorine. It agrees with chlorine and fluorine in 

 forming an acid with hydrogen ; and it agrees with oxy- 

 gen in forming an acid with chlorine." 



One of the best tests of iodine is to be found in its Test propo- 

 action on silver, which has the advantage of manifest- d by Sir 

 ing its presence in whatever state of combination it may H- Dav y- 

 exist. Water, when it contains less than one- thousandth 

 part of its weight of a hydriodate, or oxiodate, tarnishes 

 polished silver. This effect may be distinguished from 

 that produced by compounds containing sulphurets, 

 or sulphureted hydrogen, by this circumstance, that 

 the latter by being boiled with a little muriatic acid, 

 are deprived of the power of tarnishing the metal, 

 whereas solutions containing iodine, when treated in 

 the same manner, still retain it. 



In the experiments made by Sir H. Davy on na- Productions 

 tural productions which might be supposed to yield ^ uirU 

 iodine, he found that the J'uci and tdvce of the Medi- |U 

 terranean afforded it in smaller quantities than the sei 

 tie varec ; and it was only in a few cases that he could 

 find in them any traces of its existence. Slight traces 

 of it were found in the Fucus carlilaginus, the mcm- 

 Iranaceus, rubens, andjilamentosiis, and in the Ulva 

 pavonia and Ulva lima, but none in the ashes of the co- 

 rallines and sponges. He examined some specimens of 

 alkali, formed by the combustion of maritime vegetables 

 which are not submarine, but found in them no decided 

 indications of iodine. Yet he failed in his attempts to 

 obtain it from sea- water, though the use of the vol- 

 taic battery afforded some obscure results. The pro- 

 ducts separated at the positive pole were collected in a 

 small cup of gold, covered with cement, except in the 

 interior and lower part ; and this, when exposed to the 

 negative pole of a voltaic apparatus, yielded a. black 

 powder fixed in the fire, not unlike the compound form- 

 ed by heating iodine and gold together ; but it was too 

 minute to admit of chemical analysis, in order to ascer- 

 tain that it was not the same as is obtained by nega- 

 tively electrifying the oxymuriate of gold. 



See the Memoir of Gay-Lussac on Iodine, in the An- 

 nales de Chimie; or the English translation of it in the 

 fifth and sixth volumes of Thomson's Annals of Philoso- 

 phy ; and the two Memoirs of Sir Humphry Davy on 

 the same subject, in the London Philosophical Trans- 

 actions for 1814, parts i. and ii., which are repu- 

 blished in Tilloch's Philosophical Magazine ; and an 

 additional Memoir in the Transactions for 1815, part ii. 

 (H. D.) 



