THE HALOGENS 509 



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 iodio 

 acid. It is disengaged from solutions as a hydrate, HI0 3 , which loses 

 water at 170, and gives an anhydride, I 2 5 . Both these substances 

 are crystalline (sp. gr. I 2 5 5-037, HI0 3 4-869 at 0), colourless and 

 soluble in water ; 83 both decompose at a red heat into iodine and oxygen, 

 are in many cases powerfully oxidising for instance, they oxidise sul- 

 phurous anhydride, hydrogen sulphide, carbonic oxide, <fec. form 

 chloride of iodine and water with hydrochloric acid, and with bases 

 form salts, not only normal MIO 3 , but also acid ; for example, 

 KIO 3 HIO 3 , KI0 3 2HIO 3 . 83 bis With hydriodic acid iodic acid imme- 

 diately reacts, disengaging iodine, -HI0 3 + SHI = 3H 2 + 3I 2 . 



80 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, bufc 

 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, 5NaC10 3 + 3Br 2 + 3H 2 O = 5NaBr + 5HC1O 3 + HBr0 3 . 



81 If iodine be stirred up in water, and chlorine passed through the mixture, the iodine 

 is dissolved; the liquid becomes colourless, and contains, according to the relative 

 amounts of water and chlorine, either IHC1 2 , or IC1 3 , or HIO 3 . If there be a small amount 

 of water, then the iodic acid may separate out directly as 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 + 8H 2 O + 2C1 2 = IHO 3 + 5HC1. 



82 Schonebein and Ogier proved this. Ogier found that at 45 ozone immediately 

 oxidises iodine vapour, forming first of all the oxide I 2 O 3 , which is decomposed by water 

 or on heating into iodic anhydride and iodine. Iodic acid is formed at the positive pole 

 when a solution of hydriodio acid is decomposed by a galvanic current (Riche). It is 

 also formed in the combustion of hydrogen mixed with a small quantity of hydriodic acid 

 (Salet). 



83 Kammerer showed that a solution of sp. gr. 2127 at 14, containing 2HI0 3 ,9H 2 0, 

 solidified completely in the cold. On comparing solutions HI + mH 2 with HIO 3 + wH 2 O, 

 we find that the specific gravity increases but the volume decreases, whilst in the 

 passage of solutions HCl + mH 2 to HC10 3 + wH 2 O both the specific gravity and the 

 volume increase, which is also observed in certain other cases (for example, H 3 P0 3 and 

 H 3 P0 4 ). 



83 bis Ditto (1890) obtained many iodates of great variety. A neutral salt, 2(LiI0 5 )H 2 O, 

 is obtained by saturating a solution of lithia with iodic acid. There is an analogous 

 ammonium salt, 2(NH 4 IO 3 )H 2 O. He also obtained hydrates of a more complex com- 

 position, such as 6(NH 4 IO 3 )H 2 O and 6(NH 4 IO 3 )2H 2 O. Salts of the alkaline earths, 

 Ba(IO 3 ) 2 H 2 O and Sr(I0 3 ) 2 H 2 O, may be obtained by a reaction of double decomposition 

 from the normal salts of the type 2(MeI0 3 )H 2 O. When evaporated at 70 to 80 with 

 nitric acid these salts lose water. A mixture of solutions of nitrate of zinc and -an, 

 alkaline iodate precipitates Zn(IO.O*2H*O. An anhydrous salt is thrown out if nitric 



