106 OF THE GENERATION AND [SECT. in. 



render the products of less capacity for heat, so as to gain the greatest effect ; using 

 capacity to signify the whole heat these products contain, as denned art. 69. 



179. There is no question that a solid contains less heat than the same sub- 

 stance when liquid, and the substance in the liquid less than in the gaseous state ; 

 provided it remain the same chemical compound : but if to a solid, which is a mix- 

 ture of different simple substances, heat of a certain degree of intensity be applied, 

 the parts of the mixture act on each other, and gaseous products are obtained 

 which contain less heat than the mixture. This is the case with gunpowder, which 

 is a mixture of charcoal, nitre, and sulphur ; and it seems necessary in this species 

 of combustion that one of the substances composing the mixture should be easily 

 fusible. It is a completely mistaken notion to suppose that the presence of any 

 particular substance is essential to combustion ; for it must take place in any mix- 

 ture of bodies which act chemically on one another at a certain temperature, so as 

 to form new products containing less heat than the substances mixed. 



180. That which takes place in a mixture of bodies will also take place if 

 either a simple body or a chemical compound be exposed to the action of another 

 body, with which it always forms a new chemical combination if they be brought 

 in contact at a high temperature. Thus charcoal, heated to about 700, in con- 

 tact with oxygen burns ; and the new product formed is carbonic acid gas ; 

 consisting of the charcoal united to oxygen. At about 800, charcoal abstracts the 

 oxygen freely from the atmospheric air, and therefore burns. Now as the oxygen 

 gas changes neither its volume nor its elastic force, it may be inferred that the 

 whole of the heat contained in the charcoal is liberated, besides some portion of 

 that previously in the oxygen. 



181. It is important in this inquiry to know in what state the elements of 

 bodies exist, because this must greatly affect the quantity of heat. If hydrogen in 

 solid compounds be itself in its solid state, then it ought to give out less heat than 

 gaseous hydrogen : but I am of opinion that hydrogen, carbon, and other per- 

 manent gases exist in combination in the state of highly compressed gases, and not 

 in their solid state. The experiments I have to compare on combustion will be 

 found to support this opinion ; rendering it tolerably certain, that, in the range of 

 temperature we can command, these elementary bodies are never, even in the liquid 

 state, in combination ; and we are thus freed from what I had regarded as the 

 greatest difficulty in rendering the theory of combustion applicable to useful 

 objects. 1 That this theory has been so neglected, since Count Rumford paid 



1 It has been assumed by the few who have considered this subject, that the combination of oxy- 

 gen and hydrogen developed the same quantity of heat, whether the hydrogen was in a gaseous, a 

 liquid, or a solid compound ; but this could not happen if in a solid compound the hydrogen were 



