354 OXYGENATED COMPOUNDS OF CHLORINE. 



i[2HC10 4 (1 equivalent = 6 litres) + Na 2 (1 equivalent = 6 



litres)] disengages + 14'25 



[2HC10 4 (1 equivalent = 6 litres) + 2 equivalent Na 2 (1 equi- 

 valent = 6 litres)] disengages + 0'07 



[2HC10 4 (1 equivalent = 6 litres) 4- BaO (1 equivalent = 6 



litres)] disengages +14-47 



i[2HC10 4 (1 equivalent = 6 litres) + 2 equivalent BaO (1 equi- 

 valent = 6 litres)] disengages 4- 0'08 



HC10 4 (1 equivalent = 6 litres) + NH 3 (1 equivalent = 4 litres) 



disengages + 12'90 



HC10 4 (1 equivalent = 6 litres) + 2 equivalent NH 3 liberates ... + O'OO 



Potash liberated the same quantity of heat as soda, but the 

 potash solutions were taken twice as weak in order to avoid 

 precipitation of the perchlorate. 



The heat of solution of the perchlorate may now be added : 



KC10 4 + water absorbs 12*1. 



NaC10 4 (at 100) - 3-5 



i[Ba(C10 4 ) 2 ] at 100 - 0-9 



NH 4 C10 4 at20 ... ... ... - 6-36 



8. Let us moreover examine the heat of formation of perchloric 

 acid and perchlorates from their elements. 



The author and M. Vieille determined the heat of formation 

 of potassium perchlorate by mixing it in precisely equivalent 

 proportions with a combustible substance, such as potassium or 

 ammonium picrate, explosive in itself and therefore capable of 

 giving rise to an instantaneous reaction. This same substance 

 being burnt, on the other hand, by means of free oxygen, the 

 difference between the two quantities of heat measured 

 represents the excess of heat developed by the reaction by 

 means of free oxygen over the heat developed by the reaction 

 by means of combined oxygen : that is, the heat absorbed (or 

 liberated) by the decomposition of potassium perchlorate into 

 free oxygen and potassium chloride 



KC10 4 (solid) = KC1 (solid) + 20 2 . 



This quantity is derived from two experimental data only ; it is 

 independent of the heats of combustion of potassium, carbon, 

 and hydrogen, as also of that of ehlorination of potassium. 



It was found each time that the weight of the potassium 

 chloride formed (determined as silver chloride) was within ^J^ 

 of that which corresponded to the complete decomposition of the 

 perchlorate. On the contrary, the combustion of the picrate 

 was not found to be complete when the operations were con- 

 ducted in an atmosphere of nitrogen; a certain deficit being 

 noticeable in the carbonic acid, which is accounted for by the 

 free carbon and carbon monoxide. 1 For this reason it was 



1 A corresponding fraction of the ox}'gen of the perchlorate is liberated 

 owing to the simultaneous decomposition of this salt, but this in no way affects 

 the calculation. Moreover, let us bear in mind that the combustion of 

 potassium picrate converts the potash into bicarbonate, as was proved. 



