362 OXYGENATED COMPOUNDS OP CHLORINE. 



According to the last number the hydration of the iodic acid 

 does not liberate more heat than the hydrated salts do, and 

 about the same quantity as anhydrous nitric acid. 

 We have also 



J[IA (solid) + 2HIO (solid) = 2HI0 3 , I 2 5 ], + 0'62 ; 

 HIO (dissolved) = HI (dissolved) + 3 (gaseous), - 43-9. 



(i) Salts. 



|[I 2 5 + K 2 = 2KI0 3 (solid)] + 55'5 



i[I 2 5 + BaO = Ba(I0 3 ) 2 (solid)] + 34'9 



HI0 3 (cryst.) + KHO (solid) = KI0 3 (cryst.) + H 2 (solid) ... + 31-5 



i[2HI0 3 (cryst.) + Ba(HO) 2 (solid) = Ba(I0 3 ) 2 (solid) + 2H 2 (solid)] + 25'6 



The formation of solid potassium iodate, shown by the above 

 figure, liberates far less heat than the sulphate (4- 71'1, 

 anhydrous substance ; 407, hydrated substance) and potassium 

 nitrate ( + 64*2, anhydrous; +42*6, hydrated). On the contrary, 

 it exceeds to a notable degree that of the monobasic organic 

 salts, such as the acetate (+ 55*1, anhydrous ; -f 21'9, hydrated). 

 It is, however, comparable to that of the salts of the most 

 powerful organic acids, such as potassium oxalate (+ 29 '4, see 

 table, p. 127), or again, acid iodate 



KI0 3 (crystallised) + HI0 3 (solid) = KI0 3 , HI0 3 (solid), + 31, 



the value of the class of ordinary double salts. We have 

 finally from the elements 



K + I (solid) + 3 = KI0 3 (solid) + 123-9 



With I (gas) + 129-3 



KI0 3 (solid) = KI (solid) + 3 - 44-1 



KI0 3 (in solution) = KI (in solution) + 3 ... - 43'4 



8. The heat liberated by the formation of solid potassium 

 iodate from the elements (+ 129'3) exceeds that of the solid 

 bromate and chlorate. In fact, it was found that 



K + Cl + 3 = KClOg disengages + 94-6 



K + Br (gas) + 3 = KBr0 3 disengages ... + 87 "6 

 K + I (gas) + 3 = KI0 3 disengages ... + 129'3 



It is well known that the relative stability of the three salts 

 goes on increasing from the bromate to the chlorate and then to 

 the iodate. This becomes still more evident by the comparison 

 of the heat brought into play when the three solid salts are 

 decomposed, with the liberation of oxygen. 



KClOg = KC1 + 3 disengages + 11-0 



KBr0 3 = KBr + 3 + 11-1 



KI0 3 = KI + 3 absorbs - 44-1 



Not only is the decomposition of the iodate more difficult 

 owing to its endothermal character, but it is accompanied by 

 phenomena of dissociation, the dry potassium iodide absorbing 

 the free oxygen. 1 Chloric (- 12'0), bromic (- 24'8), and iodic 



1 " Annales de Physique et de Chimie," 5" se'rie, torn. xii. p. 313. 



