Mr. G. F. Rodwell on the Theory of Phlogiston. 27 



theory of phlogiston was the theory of the " materia coelestis " 

 extended in a chemical direction. Phlogistic chemistry was Car- 

 tesian chemistry. Descartes defined the physical functions of 

 the materia coelestis; Becher and Stahl defined its chemical 

 functions, and applied them to the explanation of diverse chemical 

 phenomena. Throughout the writings of Becher and Stahl 

 there is a sprinkling of Cartesianism ; they did not, however, 

 adopt the system in its entirety, but they appear to have dis- 

 carded the second and third elements, and adopted the first as 

 the parent of their own system. Enough, I think, has been said 

 in the preceding section to show clearly that the dominant func- 

 tions of the materia coelestis were conferred upon its synonym 

 phlogiston. 



The principal operations of old chemistry were performed by 

 fire ; hence pyrotechnia {irvp Te%v?;) was one of the many names 

 by which the science was once known ; " car en effet," says Le- 

 mery, " c'est par le moyen du feu qu'on vient a. bout de presque 

 toutes les operations chymiques"*. Old chemical treatises usu- 

 ally begin with the definition of various operations; and promi- 

 nent among these we find calcinatio, ignitio, cinefactio, reverbe- 

 ratio, desiccatio, sublimatio, and distillatio, — all operations of fire. 

 The only process of chemical analysis (a term which we frequently 

 find in seventeenth-century works) was effected by fire. A rude 

 fractional distillation of such bodies as could be distilled was 

 called their analysis, the different stages of the process being in- 

 dicated by the various modes of heating applied : thus the first 

 would be a water-bath ; secondly, an oil-bath ; thirdly, a bath 

 of sand or iron-filings heated below redness ; fourthly, a dull red 

 heat ; fifthly, a bright red heat ; and if there was any residuum 

 in the retort it was heated in a wind-furnace. The product of 

 each process was collected separately, and the last residuum was 

 called the "caput mortuum," or "terra damnata. }> Thus wax 

 analyzed by the above process was said to be composed of " a 

 phlegm," "a spirit," "a batter," and "a caput mortuum." 

 Such bodies as yielded no product on distillation were analyzed 

 by being calcined, either alone or with nitre or sulphur, or by 

 dissolution in an acid, evaporation to dryness, and ignition. The 

 term analysis was used in its broadest and most literal sense ; 

 immediately that a substance was split up into two or more parts 

 it was considered to be analyzed. Now, as in all known instances 

 fire appeared to act by splitting up and dissociating bodies, and 

 expelling their more volatile parts, the calcination of a metal 

 came to be considered the expulsion of its more volatile parts, and 

 the calx was called its "caput mortuum." So also sulphur and 

 phosphorus when burning were believed to lose their more vola- 

 * Cours de Chimie, p. 2. 



