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CHAPTEE IV. 



HEAT OF FORMATION OF THE NITRATES. 



1. THIS chapter will treat of the heat of formation of potassium 

 nitrate and the other nitrates, used in the manufacture of a multi- 

 tude of explosive mixtures. 



The heat of formation of potassium nitrate from its elements 

 is easy to calculate provided we know, at a temperature of 

 about 15 



(1) The heat of formation of dilute nitric acid from nitrogen 

 and oxygen. 



N 2 + 5 + H 2 + water = 2HN0 3 dil. liberates + 14'3. 



(2) The heat of formation of dilute potash from potassium 

 and oxygen. 



K 2 + + H 2 + water = 2KHO dil. liberates + 82'3. 



(3) The heat liberated in the combination of dilute nitric acid 

 and dilute potash. 



KHO dil. + HN0 3 dil. = KN0 3 dil. + H 2 liberates + 13-8. 



(4) Lastly, the heat which would be liberated if the solid 

 potassium nitrate separated itself from its dilute solution, a 

 heat which is precisely equal in absolute value to the heat 

 absorbed in the act of dissolving the same salt, but with the 

 opposite sign. 



KN0 3 dilute = KN"0 3 crystallised -f water would liberate -f 8-3. 

 The sum of these four quantities, viz. 



14-3 + 82-3 + 13-8 + 8'3 = + 1187 Cal., 

 exactly expresses the heat liberated by the union of the elements 

 of crystallised saltpetre, taken at the weight of 101 grms. 



N 2 + 6 4- K 2 = 2KN0 3 solid liberates + 118'7. 

 The formation of dissolved saltpetre from the same elements 

 would liberate + 110*4. 



From anhydrous potash, nitrogen and oxygen, N 2 -f 5 + K 2 

 = 2KN0 3 solid liberates 701. 



