12 CHEMICAL TECHNOLOGY. 



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 potting 

 partakes of the character 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 indicates its dependence 

 upon hydroplastics. Modern chemistry has enriched me- 

 tallurgy with a new department, Galvanoplastics, 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 na- 

 turally linked with a long series of arts in which water is the 

 prime agent in modifying and directing the force, afiinity ; 

 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 power- 

 ful and contrary effects ; the solvent for salts, in which they 

 are decomposed and resolved into new and useful compounds. 

 The manufacture of sulphuric acid, usually regarded as the 

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

 transforming common salt into the alkali soda, introduces a 

 series of various connected and derivative arts, conducted on 

 a. large scale, whose elements are to be found in plastics, and 

 which may constitute a convenient division of chemics, called 



