CHEMICAL TECHNOLOGY. 11 



subjected to action. The air performs less important func- 

 tions, as a direct agent ; but, in conjunction -with fuel, it is 

 indirectly an indispensable agent, in developing heat by the 

 union of its oxygen with the carbon and hydrogen of fuel. 

 Fuel is, however, the true agent in this case, practically con- 

 sidered, because it can be handled, weighed, and measured, by 

 the artisan, and is indispensable in the reduction of metallic 

 ores. We therefore regard fuel as the source of heat in the 

 arts ; and since the larger proportion of the more important 

 technical processes are more or less controlled by heat, it must 

 be viewed as the principal agent or modifier of affinity. 

 Hence the sources and management of heat should be the 

 first subject treated of in a classified narration of technical 

 processes. It may be followed by its application to the warm- 

 ing of buildings, which, in its manifold aspects of economy, 

 convenience, safety, and the health of man, embraces the 

 forms of apparatus in which it is employed, and the subject 

 of ventilation. 



More naturally connected with fuel than with any other 

 department of the arts are the means of obtaining and of 

 extinguishing fire : the preparation of those mixtures of 

 combustibles with condensed forms of oxygen, such as gun- 

 powder, and other projectile and destructive agents, together 

 with their allied compositions for ornamental displays of fire. 

 These may be embraced under the term Pyrotechny. 



The whole of the first subject, included under the term 

 Calorics, admits of the three subdivisions or groups : Fuel and 

 Furnaces, Warming and Ventilation, and Pyrotechny. 



One of the simpler applications of heat to modify mineral sub- 

 stances, is the fusion of sand and alkali to glass, which is highly 

 plastic when sufficiently heated, and in that state receives the 

 form which it retains on cooling. Another application is to the 

 semi-fusion or baking of clay-ware, which, having been previ- 

 ously plastic by admixture with water, and having then received 

 its form, is heated to a point below perfect fusion to give that 

 form permanence. Allied to these is another plastic art : the 

 making and use of cements and mortars, including plaster- 



