CHEMICAL TECHNOLOGY. 195 



fire ; the preparation of those mixtures of combustibles with con- 

 densed forms of oxygen, such as gunpowder, and other projectile and 

 destructive agents, together with their allied compositions for orna- 

 mental displays of fire. These may be embraced under the term Pyro- 

 techny. 



The whole of the first subject, included under the term Calorics, 

 admits of the three subdivisions or groups : Fuel and Furnaces, Warm- 

 ing and Ventilation, and Pyrotechny. 



One of the similar applications of heat to modify mineral substances, 

 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 previously 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- 

 casting, and making artificial stone. All these are embraced under the 

 general term of Plastics ; of which glass-making is Pyroplastics ; 

 cements, Hydroplastics ; while the art of pottery partakes of the charac- 

 ter of each. 



Another important but more complex application of fire is to 

 Metallurgy, wherein fuel is both the source of heat and the chief means 

 of reducing ores to the metallic state. It will be observed, that while 

 the fluxing of ores naturally connects metallurgy with the pyroplastic 

 arts of glass and pottery, the construction of furnaces and moulds indi- 

 cates its dependence upon hydroplastics. Modern chemistry has en- 

 riched metallurgy with a new department, Gaivanoplastics, and with a 

 variety of processes in which the metallurgic treatment of ores is effected 

 by solutions. We may, therefore, conveniently divide the subject into 

 Pyrometallurgy and Hydrometallurgy. For the present, it is proper to 

 regard Photography as a branch of the latter, with which it stands in 

 intimate connection. 



Metallurgy and Plastics, having each their branches, in which 

 aqueous action plays a conspicuous part, are thus naturally linked with 

 a long series of arts in which water is the prime agent in modifying 

 and directing the force, affinity; and the connection is still further 

 established by the fact, that the substances acted on are mostly confined 

 to those of the preceding classes, alkali, earth, and metal. The arts in 

 the present class, having for their chief object the preparation of simple 

 chemical compounds, acid, oxide, and salt, and being conducted 

 on purely chemical principles, have received the general term of Chemics. 

 Water is the medium of action, the solvent for acid and alkali, in which 

 they exert their powerful and contrary effects ; the solvent for salts, in 

 which they are decomposed and resolved into new and iiseful com- 

 pounds. The manufacture of sulphuric acid> usually regarded as the 

 keystone of the more purely chemical arts, and its use in transforming 



Q 2 



