v.] CHEMICAL ENERGIES. 51 



that is to say, instead of giving out heat in the act of 

 formation, it takes up 9,232 heat-units, whicli reappear 

 as heat when it is decomposed. 



Thermo-positive compounds are never products of com- 

 bustion, but are always formed by indirect methods. As 

 a general rule, they appear to be less stable and more 

 chemically active than thermo-negative compounds. Many 

 compounds of nitrogen are chemically very active ; nitrous 

 oxide, ali'eady mentioned, is by no means the most re- 

 markable of these. Gun-cotton and the fulminating salts 

 are compounds of nitrogen, and are in all probability highly 

 thermo-positive. It has often excited surprise that the 

 compounds of nitrogen should be so active when nitrogen 

 is itself so inert, but most probably the inertness of un- 

 combined nitrogen is in some way connected with the 

 power of nitrogen to take up large charges of energy in 

 its compounds. 



Peroxide of hydrogen is from tliis point of view a very Peroxide 

 remarkable substance. It is altogether misleading to write °gjj7 

 its symbol 



HO. 



It is really a thermo-positive and very unstable oxide of 

 water : ^ it is easily decomposed into water and oxygen, 

 and in this decomposition heat is produced. Writing 

 water as before, 



HO* — 34,462 6, 



peroxide of hydrogen should be written 



(H Oi — 34,462 6) Qi + 10,904 6.^ 



in the act of decomposition, evolves a considerable amount of heat : and 

 they estimate that not less than 1,154 units of heat are evolved in the 

 separation into its elements of a quantity of nitrous oxide which contains 

 one gramme of oxygen." (Miller's Chemistry, Appendix.) Multiplying 

 1,154 by 8 for the atomic weight of oxygen, we have 9,232, the thermal 

 equivalent in the text. 



^ It is not necessary for my present purpose to enter on the question as 

 to its being a compound of antozoue with water. 



2 Fabre and Silbermaun " estimate the heat evolved during the liberation 

 of one gramme of oxygen from peroxide of hydrogen at 1,363 heat-units." 

 (Miller's Chemistry, Appendix.) Multiplying by 8 as before, we have 

 10,904 as the thermal equivalent. 



E 2 



