TIIK HAUMIKNS 501 



solid black product of metalepsis, generally known as iodide of nitrogen, 

 although it probably contains hydrogen, 3NH 3 + 2I 2 = 2XH 4 I + NHI 2 . 

 However, the composition of the product is variable, and with an excess 

 of water XT;, seems to be formed. Iodide of nitrogen is no less explosive 

 than nitrogen chloride. In the action of iodine on sodium hydroxide 

 no bleaching compound is formed (whilst bromine gives one), but a 

 direct reaction is always accomplished with the formation of an iodate 

 GNaHO + 3I 2 = 5NaI + 3H 2 O + NaIO 3 (Gay-Lussac). Solutions of 

 other alkalis, and even a mixture of water and oxide of mercury, act in 

 the same manner. This direct formation of iodic acid, HIO 3 = IO 2 (OH), 

 shows the propensity of iodine to give compounds of the type IX 5 . 

 Indeed, the propensity of iodine to form compounds of a higher type 

 clearly evinces itself in many ways. But it is most important to turn 

 attention to the fact that iodic acid is easily and directly formed by the 

 action of oxidising substances on iodine. Thus, for instance, strong 

 nitric acid directly converts iodine into iodic acid, whilst it has no 

 oxidising action on chlorine. 79 This shows a greater affinity in iodine for 

 oxygen than in chlorine, and this conclusion is confirmed by the fact 

 that iodine displaces chlorine from its oxygen acids, 80 and that in the 

 presence of water chlorine oxidises iodine. 81 Even ozone or a silent 

 discharge passed through a mixture of oxygen and iodine vapour is able 

 to directly oxidise iodine 82 into iodic acid. It is disengaged from solu- 



79 The oxidation of iodine by strong nitric acid was discovered by Connell ; Millon 

 showed that it is accomplished, although more slowly, by the action of the hydrates of 

 nitric acid up to HNO 3 ,H 2 O, but that the solution HNO r ,,2H 2 O, and weaker solutions, 

 do not oxidise, but simply dissolve, iodine. The participation of water in reactions is 

 seen in tin's instance. It is also seen, for example, in the fact that dry ammonia com- 

 bines directly with iodine for instance, at forming the compound I 2 ,4NH 5 whilst 

 iodide of nitrogen is only formed under the action of water. 



- Bromine also displaces chlorine for instance, from chloric acid, directly forming 

 bromic acid. If a solution of potassium chlorate be taken (75 parts per 400 parts of 

 water), and iodine be added to it (80 parts), and then a small quantity of nitric acid, 

 chlorine is disengaged on boiling, and potassium iodate is formed in the solution. In 

 this instance the nitric acid first evolves a certain portion of the chloric acid, and the 

 latter, with the iodine, evolves chlorine. The iodic acid thus formed acts on a further 

 quantity of the potassium chlorate, sets a portion of the chloric acid free, and in this 

 manner the action is kept up. Potilitzin (1887) remarked, however, that not only do 

 bromine and iodine displace the chlorine from chloric acid and potassium chlorate, but 

 also chlorine displaces bromine from sodium bromate, and, furthermore, the reaction does 

 not proceed as a direct substitution of the halogens, but is accompanied by the formation 

 of free acids; for example, 5NaClO 3 + 8Br 2 + 8H 2 O = 5NaBr + 5HClO 5 + HBrO 5 . 



J1 If iodine be stirred up in water, and chlorine passed through it, then the iodine is 

 dissolved; the liquid becomes colourless, and contains, according to the mass of water 

 and chlorine, either the compounds IHC1 2 , or IC1 3 , or HIO 5 . If there be a small amount 

 of water, then the iodic acid may separate out directly in crystals, but a complete con- 

 version (Bornemann) only occurs when not less than ten parts of water are taken to 

 one part of iodine IC1 + 3H 2 O + 2C1 2 = IHO 5 + 5HC1. 



s - S ( -liiinebein and Ogier proved this. Ogier found that at 45 ozone immediately 



