OXYGENATED COMPOUNDS OF BROMINE. 357 



liberates also -f 7'4 ; a value comparable to the heat of for- 

 mation of the secondary hydrated sulphuric acid. These 

 numbers tend to support the opinion that considered the 

 hydrated perchloric acids as the last indication of the penta- 

 basic character recognised in perchloric acid. Such a character 

 would only declare itself by the formation of hydrates with an 

 abundant liberation of heat, perchloric acid only forming 

 monobasic salts. In another series HRQ 3 it has been shown 

 already how to pass from monobasic chloric and nitric acids to 

 tribasic phosphoric acid by means of iodic acid, which presents 

 certain intermediate characters. 1 



We see by these details how thermo-ehemistry accounts for 

 the characteristic properties of perchlorates, and especially for 

 the singular opposition which exists in the energetic oxidising 

 reactions of the concentrated acid, and the great stability of the 

 diluted acid. 



4. OXYGENATED COMPOUNDS OF BROMINE. 



1. The thermal formation of bromic acid, potassium bromate, 

 and potassium hypobromite was studied. 



2. Very pure potassium bromate was used, which had been 

 prepared and analysed by the author himself. 



It was dissolved in water. 



KBr0 3 -f water (1 part of salt -f 50 parts of water), at 11, 

 absorbs - 9'85 Cal. 



This solution was reduced by means of an aqueous solution 

 of sulphurous acid ; also the heat liberated by the union of the 

 diluted bromic acid with the potash was measured ; this is 

 essentially the same as the heat of neutralisation of chloric, 

 hydrobomic, and hydrochloric acids (4- 13*7) by the same 

 base. 



3. All calculations being made, it was found for bromic acid 

 that - 



J [Br 2 (liq.) + 5 -f H 2 + water = H 2 0, Br 2 5 (diluted)] 



absorbs - 24'8. 



Thomsen, having reduced the same acid by means of stan- 

 nous chloride, found 21'8, but on substituting in the 

 calculation of his experiments the number 3 8 '5, which seems to 

 be the more accurate, 2 for the number 38'0, which he adopted 

 for the chlorination of stannous chloride, he also arrived at 

 - 24-8. 



From this we get 



i[Br 2 (gas) + 5 -f H 2 + water = H 2 0,Br 2 O 5 (diluted)], - 2O8 ; 



1 " Annales de Chimie et de Physique," torn. xii. pp. 313, 314. 



2 Ibid., 5 e se>ie, torn. v. p. 330 



