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



a mode of thought different from that which had prevailed at any- 

 prior period : these were the Chemists. Whatever their ultimate 

 object may have been (alchemy, iatro-chemistry, metallurgic 

 chemistry), their immediate pursuits led them to study the struc- 

 ture of matter, the varying nature of different kinds of matter, 

 and the modus of their change under the most artificial and 

 forced conditions which could be commanded. Rejecting the 

 four-element theory as expressed by the ancients, the chemists 

 adopted three principles, which they designated sal, sulphur, 

 mercurius, and before we go further it is important for us to un- 

 derstand accurately the right significance of these terms. It is 

 not unfrequently imagined that they are to be taken in their 

 literal sense; but no idea can be more erroneous, or more likely 

 to lead to false impressions as regards the early history of che- 

 mistry. The terms were used exactly as we now use the term 

 alkali or salt in chemistry ; not one alkali, not common salt, 

 but all bodies possessing certain qualities in common, and taking 

 their name from the first known of their class, or from some do- 

 minant quality which they possess in common. The salt, sul- 

 phur, and mercury of the chemists are "principia," not "corpora;" 

 they are " avaXoya " — representative bodies, types of classes, 

 types of qualities; by them is expressed in other terms the fire, 

 air, water, and earth of the ancients. Fire is included under 

 the term sulphur — the principle of combustibility. Air and 

 water (liquidity and gaseity) are included under the term mer- 

 cury — the principle of volatility. Finally, earth is included under 

 the term salt — the principle of fixity and solidity. 



Empedocles adduced a simple experiment in support of the 

 four-element theory : he burnt wood, and pointed out the pre- 

 sence of the elements : — visible fire ; air represented by the 

 smoke ; water exuding from the charring wood ; and earth re- 

 maining on the hearthstone in the form of ash. The chemists 

 as readily proved the presence of their three elements : — the com- 

 bustible flame-generating part of the wood they said is sulphur, 

 the volatile part is mercury, the ash is salt, Paracelsus says, 

 very concisely, " For whatsoever fumes and evaporates in the fire 

 is mercury ; whatsoever flames and is burnt is sulphur ; and all 

 ash is salt"*. 



Beguinus, in his famous Tyrocinium Chymicum-f, has extended 



* De Rerum Natura, lib. vi. 



t This work was published in Paris in 1615, and was reprinted in various 

 parts of Europe in 1618, 1624, 1637, 1650, 1665, and 1669. The above 

 is extracted from the 1669 edition, which was published simultaneously 

 with Becher's Physica Subterranea. This edition is elaborately paraphrased 

 by Gerard Blasius, assisted by the writings of twenty-seven of the most 

 eminent chemists who had preceded him. 



