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THE POPULAR SCIENCE MONTHLY. 



ties of substances which form the foun- 

 dation of tlie science, and constitute 

 Liebig's first stage in its progress. 



Although the second stage — the 

 formation of general ideas or theories 

 — is a sequence of the first, and im- 

 plies accumulated observations to be 

 explained, yet it was begun early. 

 The doctrine of the four primitive ele- 

 ments, fire, air, earth, and water, was 

 the first chemical theory, and sufficed 

 for many centuries. To these four ele- 

 ments of Aristotle, which were regarded 

 as the four fundamental causes of the 

 pliysical properties of matter, were 

 added three new elements — mercury, 

 sulphur, and salt — which also stood 

 for certain properties and causes of 

 change, rather than concrete bodies. 

 Mercury represented volatility, and 

 was supposed to give this property to 

 matter; sulphur was connected with 

 changeableness by fire, or combustibili- 

 ty, and salt represented fixity, like the 

 salts found in ashes. On this view, 

 alcohol, or aqua vitae, was regarded 

 as "sulphurous vegetable mercury," 

 which only meant that it was inflam- 

 mable and volatile. Hence Basil Valen- 

 tine says : " When a rectified aqua vitfe 

 is kindled, its mercury and sulphur sep- 

 arate ; the sulphur burns quite vividly, 

 for it is pure fire, and the delicate mer- 

 cury flies into the air and returns to its 

 original chaos." 



Such rude ideas answered to begin 

 the work of chemical theorizing, but the 

 increase of facts at length showed that 

 they were contradictory and absurd. 

 About a hundred years before the time 

 of Priestley, Beccher, a German chem- 

 ist, in undertaking to correct the doc- 

 trine of salt, sulphur and mercury, 

 struck a new conception which soon 

 grew into a comprehensive and impor- 

 tant chemical theory. In working with 

 sulphur, he sagaciously detected the 

 analogy between the formation of sul- 

 phuric acid from sulphur and the re- 

 duction of metals to an earthy form 

 (calx). The metal was supposed to 



consist of an earth, and something 

 which, in the process of combustion, 

 was separated from it ; in like manner 

 sulphur was supposed to consist of an 

 acid and something that was separated 

 from it, by burning, and to this some- 

 thing Stahl afterward gave the name 

 of phlogiston — Greek for combuatiMe. 

 So intimately and extensively were fire 

 and combustion involved with chemi- 

 cal changes, that a theory of combus- 

 tion was regarded as the same thing as 

 a theory of chemistry. It was assumed 

 that all combustible bodies are com- 

 pounds. One of the constituents was 

 supposed to be dissipated during the 

 process, while the other remained be- 

 hind. The part dissipated, phlogiston, 

 was held to be the same in all com- 

 bustible bodies whatever, and hence 

 the differences among them depended 

 upon the residues. On this view, the 

 property of combustibility is always 

 owing to the presence of phlogiston, 

 and fire, or inflammation, to its escape. 

 Phlogiston was ^ommunicable from 

 body to body. "When phosphorus is 

 burned it loses its phlogiston, and an 

 acid remains. But if now the acid is 

 heated in a retort with charcoal-pow- 

 der, sugar, or resin, these combustibles 

 are deprived of their phlogiston, which, 

 passing over to the acid, reproduces 

 phosphorus. Bodies saturated with 

 phlogiston were said to be pMoghti- 

 cated^ and, when deprived of it, were de- 

 pMogkticated, processes which might 

 be as partial or complete as the varia- 

 tions of combustive phenomena. These 

 ideas were founded upon experiments 

 so decisive that, when the existence of 

 the principle itself was once admitted, 

 the explanation was entirely satisfac- 

 tory. "There are ideas," says Liebig, 

 "so great and vast that, even when en- 

 tirely perforated, as it were, in all di- 

 rections, they leave enough of matter to 

 occupy the powers of thought of man- 

 kind for a century. Such a vast idea 

 was that of phlogiston. The question 

 as to its material existence was void of 



