508 PRINCIPLES OF CHEMISTRY 



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 aniodate, 6NaHO + 31^= 5NaI + 3H 2 + NaIO 3 

 (Gay-Lussac). Solutions of other alkalis, and even a mixture of water 

 and oxide of mercury, act in the same manner. 79 This direct formation 

 of iodic acid, HIO 3 = IO 2 (OH), shows tlie propensity of iodine to give 

 compounds of the type IX 5 . Indeed, this capacity of iodine to form 

 compounds of a high type emphasises 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 bls 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 



found that iodide of nitrogen, NHI 2 , dissolves in an excess of ammonia water, and that 

 with potassium iodide the solution gives the reaction for hypoiodous acid (the evolution 

 of iodine in an alkaline solution). This shows that HIO participates in the formation 

 and decomposition of NHI 2 , and therefore the condition of the iodine (its metaleptio 

 position) in them is analogous, and differs from the condition of the halogens in the 

 haloid-anhydrides (for instance, NO 2 C1). The latter are tolerably stable, while (the 

 haloid being designated by X) NHX 2 ,~NX 3 , XOH, RXO (see Chapter XIII. Note 48), &c., 

 are unstable, easily "decomposed with the evolution of heat, and, under the action of 

 water, the haloid is easily replaced by hydrogen (Selivanoff), as would be expected in 

 true products of metalepsis. 



79 Hypoiodous acid, HIO, is not known, but organic compounds, BIO, of this type 

 are known. To illustrate the peculiarities of their properties we will mention one 

 of these compounds, namely, iodosobenzol, CeH 5 IO. This substance was obtained 

 by Willgerodt (1892), and also by V. Meyer, Wachter, and Askenasy, by the action, 

 of caustic alkalis upon phenoldiiodochloride, C 6 H 5 ICJ.2 (according to the equation,, 

 C 6 H 5 IC1 2 + 2MOH = C a H 6 IO + 2MC1 + H 2 O). lodosobenzol .is an amorphous yellow sub- \ 

 stance, whose melting point could cot be determined because it explodes at 210,, 

 decomposing with the evolution of iodine vapour. This substance dissolves in hot water 

 and alcohol, but is not soluble in the majority of other neutral organic solvents. If: 

 acids do not oxidise C 6 H 5 IO, they give saline compounds in which iodosobenzol appears 

 as a basic oxide of a diatomic metal, CeH 5 I. Thus, for instance, when an acetic acid 

 solution of iodosobenzol is treated with a solution of nitric acid, it gives large monoclinic 

 crystals of a nitric acid salt having the composition C 6 H 5 I(NO 3 ) 2 (like Ca(NO 3 )2); 

 In appearing as the analogue of basic oxides, iodosobenzol displaces'iodine from potassium' 

 iodide (in a solution acidulated with acetic or hydrochloric acid) i.e. it acts with its 

 oxygen like HC1O. The action of peroxide of hydrogen, chromic acid, and other similar 

 oxidising agents gives iodoxybenzol, C 6 H 5 IO 2 , which is a neutral substance i.e. incapable^ 

 of giving salts with acids (compare Chapter XIII. Note 48). 



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

 bowed that it is effected, although more slowly, by the action of the hydrates of nitric 

 acid up to HNO 3 ,H 2 O, but that the solution HNO 3 ,2H 2 O, and weaker solutions, do not 

 oxidise, but simply dissolve, iodine. The participation of water in reactions is seen in 

 this instance. It is also seen, for example, in the fact that dry ammonia combines 

 directly with iodine for instance, at Q forming the compound I-j^NHy whilst iodide of 

 nitrogen is only formed in presence of water. 



