Mr. G. F. Rod well on the Theory of Phlogiston. 29 



there is no sudden and gigantic stride ; a theory proceeds by 

 slow evolution until it dominates or is destroyed. It was thus 

 with the theory of phlogiston : arising under the most favour- 

 able conditions it attained full development, became most car- 

 dinal, most sovereign, and fell. For twenty-eight years it was 

 looming a half-formed thing through the mists of chemistry; 

 for thirty-four years it was growing in strength and proclaiming 

 its dynasty; for fifty-four years it was dominant, and it was fully 

 ten years yielding up the ghost. There are men amongst us 

 now who have listened to the echoes of its departing steps. 



Becher and Stahl were the prophets of anew mode of chemical 

 thought, essentially classificatory, systematic, and syncretistic. In 

 their day chemistry was at the commencement of a period of trans- 

 ition, and they bridged the gap which existed between empirical 

 chemistry and modern chemistry. They did not collect the mate- 

 rials for the structure, they did not altogether construct it, but 

 they designed it, and. helped in the work of building. Albeit a 

 bad bridge, and built upon shifting sands,, yet it was a channel of 

 escape from mystic science, and many passed over to take refuge 

 on the other side. 



The theory of phlogiston was highly ingenious, and it was 

 elaborated with great assiduity and perseverance, but it was not 

 founded upon direct experimental deductions ; indeed this could 

 not be the case, on account of the subtlety of the supposed entity, 

 and the consequent impossibility of experimenting with it. 

 Phlogiston was believed to be something like that subtle me- 

 dium which has for ages been known by its present name, the 

 ather ; indeed phlogiston is sometimes called " materia ignea 

 cetherea"*. It had never been seen; its real nature and pro- 

 perties were entirely unknown ; for it had never been separated 

 in the free state : all was conjecture; yet it was agreed to refer 

 certain phenomena of chemical change to its absorption or re- 

 jection by the mutating substance. Macquer says we cannot 

 tell how phlogiston is fixed by substances, and adds, very un- 

 philosophically, " without pretending to guess the cause of the 

 phenomenon, let us rest contented with the certainty of the fact, 

 the knowledge of which will undoubtedly procure us consider- 

 able advantages." (We cannot but think that this " resting eon- 

 tent" with the theory did much to retard chemistry during the 

 phlogistic period.) The phlogistians were most assiduous in 

 collecting " Instantice convenientes in naturd calidi," but they 

 were slow to apply " rejectio naiurarum a forma calidi"f. The 

 generalization was too hasty and was insufficiently supported by 



* Vide Conspectus Chemice Theoretico-practicce e dogmatibus Becheri 

 et Stahlii. AuctoreD. Joanne Junckero. 1744. 

 t Novum Organum, lib. ii. aphs. 11 & 18. 



