192 



IODINE. 



Iodine. 



Charcoal. 



Sulphur. 



Phospho- 

 ru. 



It has the property of combining with almost all the 

 metals. In this, and some other properties, it resem- 

 bles the ox) muriatic or chlorine gas; but much less 

 lic.it is evolved than by the combination of the metal 

 with this last-mentioned substance. One probable rea- 

 son of this is, that iodine is previously in a solid state. 

 I-'rom this property, however, Dr. Thomson classes it 

 with chlorine and oxygen, under the title of supporters 

 of combustion. In this particular, it is to be observed, 

 it also resembles sulphur, which combines with metals 

 with an evolution of caloric. 



Potassium, during its union with iodine, emits a pale 

 blue flame. The result of the union is a white com- 

 pound fusible at a red heat, soluble in water, of an 

 acrid taste, and re-yielding the iodine when treated 

 with sulphuric acid. 



With iron, mercury, tin, zinc, and lead, it forms com- 

 pounds, fusible at a moderate heaf, and generally of 

 bright colours. Most of these are capable of forming 

 compounds with potass, from which sulphuric acid 

 evolves the iodine. 



Under water, zinc and iodine combine on the appli- 

 cation of a moderate heat. 100 parts of iodine combine 

 witii about 26.225 of the metals. These metallic com- 

 pounds are called iodurets. Iron is acted on in the 

 same manner. The ioduret of iron is brown, and fusi- 

 ble at a red heat. Its solution in water is of a light 

 green like the muriate, or what Gay-Lussac calls the 

 chloruret of iron, from supposing that it is not a com- 

 bination of a metalic oxide with muriatic acid, but of 

 the pure metal with chlorine. 



The ioduret of tin is very fusible. When in powder 

 it has a dark orange colour. It was found by Sir H. 

 Davy to possess the characters of an acid. It combin- 

 ed with the alkalies without depositing any oxide. 

 The ioduret of antimony is like the preceding, fusible, 

 and resembles it when in the state of powder. The io- 

 durets of lead, copper, bismuth, silver, and mercury, are 

 insoluble in water, a property in which they diner from 

 those of the more oxidable metals. 



There are two iodurets of mercury, the yellow and 

 the red, depending on differences of proportion in the 

 combinations. The yellow ioduret contains one half 

 less iodine than the red. 



The iodurets of the metals are decomposed by chlo- 

 rine, which unites with the metals, and expels the io- 

 dine. When ioduret of potassium is heated in contact 

 with chlorine, chloruret of potassium (the substance 

 called muriate of potass) is formed, the violet gas ap- 

 pears, but soon unites with chlorine, and they form by 

 their union a peculiar acid compound ; but towards the 

 end of the process, as the proportion of chlorine dimi- 

 nishes, the violet coloured gas again appears. Ioduret 

 of silver gives similar phenomena. Iodine, however, 

 appears to possess a stronger attraction for most of the 

 metals than oxygen. 



Charcoal has no action on iodine, either at high or 

 low temperatures. 



With sulphur, iodine forms a weak compound of a 

 greyish black colour, radiated like sulphuret of antimo- 

 ny, and iodine is separated from it when distilled with 

 water. 



With phosphorus it combines in different propor- 

 tions with the disengagement of heat without light. 

 One part of phosphorus and eight of iodine form a 

 compound of a red orange brown colour, fusible about 

 212", and volatile at a higher temperature. 



With 16 parts of iodine to 1 of phosphorus, a greyish 

 Mack crystallized compound is formed, fusible at 84. 



With 24 parts a black compound is obtained, -partially 

 fusible at 115. 



The iodurets of phosph<frus exhale, wherr moistened, 

 acid vapours. These are an acid suhstAiicr, bearing the 

 game relation to iodine that muriatic acid doestochlorine; 

 and those who still maintain that chlorine is a compound 

 of muriatic acid with oxygen, and that muriatic acid is ob- 

 tained from it by separating the oxygen, may consider 

 iodine as a compound containing oxygen, and the acid 

 produced from it as comparatively a. simple substance, 

 being deprived of the oxygen contained in the iodine/ 

 But in this case, as in the former, the presence of hy- 

 drogen is essential to the formation of acid from the al- 

 leged compound. This most commonly happens from 

 the presence of water ; and for this, among other rea- 

 sons, Gay-Lussac and Sir H. Davy consider the che- 

 mical change induced as consisting in the union of a 

 simple substance, chlorine in the one case, and iodine 

 in the other, with hydrogen. Though fully aware of 

 the difficulty of deciding this question in the present 

 state of science, we shall adopt the phraseology and no- 

 menclature which depend on the latter of these theo- 

 ries, and which are in comformity with the doctrines of 

 chlorine and muriatic acid, as stated in our article CHE- 

 MISTRY. We shall keep in view that an acid is ob- 

 tained from iodine by combining it with hydrogen, 

 and this we shall call tile hydriodic acid. This indeed 

 is a matter of fact, whether iodine is regarded as a sim- 

 ple or a compound body. 



Hydrogen, whether dry or moist, has no action on 

 iodine at the ordinary temperature ; but when a mix- 

 ture of it with iodine is exposed to a red heat in a 

 tube, they unite, and hydriodic acid is produced, which 

 shews its presence by giving a reddish brown colour 

 to water. The cause of this colour will afterwards ap- 

 pear. In this process, 100 parts of iodine absorb only 

 .849 by weight of hydrogen. 



Hydriodic acid is produced most easily by means of 

 ioduret of phosphorus. In order to procure it free from 

 any admixture of phosphuretted hydrogen, it is neces- 

 sary to employ a compound in which the phosphorus 

 does not exceed a ninth part. Tins ioduret was, in the 

 experiments of Gay-Lussac, moistened with pure water, 

 or, what is better, water containing some hydriodic 

 acid previously formed. Another method is to put 

 the iodine into a small tube, which is then to be re- 

 versed in mercury, and the air expelled from it, by in- 

 troducing a glass rod which nearly fills it ; after which 

 the phosphorus is brought in contact with the iodine, 

 by being made to rise through the mercury ; the sub- 

 stances immediately combine and the hydriodic gas is 

 disengaged, and may be collected, by putting the open 

 extremity of the tube under a glass jar standing in the 

 mercury. The gas, however, begins to be decomposed 

 as soon as it comes in contact with the mercury. The 

 iodine combines with the mercury, forming a greenish 

 yellow ioduret. By agitating the mercury, this' de 

 composition may be made to extend to the whole gas 

 present, and a volume of hydrogen is left exactly equal 

 to one-half of the hydriodic gas. The contact of zinc 

 and potassium produces the same result. 



Hydriodic acid gas is colourless, and has an odour 

 similar to that of muriatic acid. Its taste is intensely 

 acid. It saturates its own bulk of ammoniacal gas. Chlo- 

 rine deprives it of its hydrogen, and reduces it to the 

 state of iodine, while itself assumes the form of muriatic 

 acid. This acid is denominated by Gay-Lussac hydro- 

 chloric, being formed of chlorine and hydrogen, and this 

 name represents the analogy subsisting between it and 



Action F 

 iodine on 

 hydrogen* 



Mode of ob- 

 taining hy- 



dnodic acli 



its propr- 

 ties. 



