CHLORIC ACID. 347 



We deduce from these numbers 



J[S0 2 (dissolved) 4- (gas) + H 2 = H 2 S0 4 (dilute)] 4- 3215; 

 and consequently 



i[H 2 4- C1 2 + 6 -f water = H 2 0, C1 2 5 (dilute)] - 12'0. 

 This number depends on the heats of formation of water, 

 hydrochloric and sulphuric acids. 



6. Hence it is that the formation of dilute chloric acid from 

 its elements 



[C1 2 4- 6 4- H 2 4- water = H 2 0, C1 2 5 (dilute)], liberates 



+ 22-5. 



The conversion of dilute chloric acid into dilute hydrochloric 

 acid and gaseous oxygen 



HC10 3 (diluted) = HC1 (diluted) + 3 , liberates 4- 16'8. 



This value plays an important part in oxidations. 



7. It is the same for dissolved chlorates, decomposed into 

 chlorides and free oxygen ; for the heat liberated in the action 

 of various bases on hydrochloric and chloric acids is essentially 

 the same. In fact, the following numbers were found at 

 19: 



J[2HC1 (diluted)] J[2HC10, (diluted)] 



+ *[K 2 (diluted)] +13-7 +13-7 



+ |[Na 2 (diluted)] + 13-7 + 13-7 



+ |[BaO (diluted)] + 13-85 + 13-8 



8. Returning to the heats of solution of chlorides and chlorates, 

 the values of which have been given elsewhere, 1 we obtain the 

 heat of decomposition of chlorates into chlorides and oxygen 

 (referred to the ordinary temperature) 



KC10 3 (solid) = KC1 (solid) 4- 3 4- ll'O ; 

 instead of 4- 9 '8, given by Thomsen. These values are very near 

 each other. It was also found that 



NaC10 3 (solid) = NaCl (solid) 4- 3 4- 12'3. 

 J[Ba (C10 3 ) 2 (solid) = BaCl 2 (solid) 4- 30 J 4- 12-6. 



Even at the temperature of the reactions, that is to say, at 

 500 or 600, the quantities of heat, for solid salts, are nearly 

 the same, as may be established by calculation. For instance, 

 the specific heat of potassium chlorate for the equivalent weight 

 KC10 3 is equal to 23'8 ; for KC1 4- 3 , the sum of the specific 

 heats amounts to 23 '3. The term U V, which expresses the 

 variation of the heat of combination, is therefore equal to 



4- 0-5 cal. (T - t) ; 



or, for an interval between zero and 500, 0'25 Cal., which is 

 an insignificant increase in comparison with 4-11-0. 



1 " Annales de Chimie et de Physique," 5' se*rie, torn. iv. pp. 103. 104. 



