CHAPTEK III. 



HEAT DISENGAGED. 



1. THE total quantity of heat disengaged during an explosive 

 reaction, can be experimentally measured in a calorimeter. 

 The apparatus employed for this purpose will be described 

 further on. The quantity of heat is generally positive. There are, 

 however, certain reactions, such as that of tartaric acid on sodium 

 bicarbonate, which develop gas and at the same time produce 

 cold. The explosion of the containing vessel might thus 

 coincide with the latter phenomena. It would be the same 

 with the explosion of a vessel containing a compressed gas. But 

 these are exceptional cases, and outside of the ordinary applica- 

 tions of explosives. 



2. The heat developed can be calculated after deducting the 

 mechanical effects, when the products of the explosive reaction 

 are exactly known, and when the heat of formation of the original 

 substances, as well as of the products, from the elements is also 

 known. It is only necessary to deduct the former quantity of 

 heat from the latter to obtain the heat developed daring the 

 explosion. 



3. The calculations are made from the thermo-chemical data 

 contained in the tables (pp. 125-144). These tables are taken 

 from the author's " Essai de Mecanique Chimique." 



4. The quantity of heat necessary to raise 1 grm. of water 

 from to 1 is generally called a calorie. This unit is every- 

 where employed to represent the heat disengaged by the trans- 

 formation of 1 grm. of matter. 



But the magnitude of the quantities of heat disengaged when 

 chemical reactions are referred to the equivalent weights 

 (expressed in grms.) has rendered necessary the use of a unit 

 a thousand times greater ; this is the large Calorie, the quantity 

 of heat necessary to raise 1 kgm. of water from to 1. 



5. To find, for example, the heat disengaged by the detonation 

 of nitroglycerin, under constant pressure, in the open air, 



2(C 3 H 5 N 3 9 ) = 6C0 2 + 5H 2 liquid + 3N 2 + 0. 

 According to the tables, the heat disengaged by the union of 



