CHEMISTRY OF THE SEVENTEENTH CENT. 233 



while he regards the reduction of the calx into the metallic form as a 

 synthetical process that is, a re-combination of calx and phlogiston. 

 He has an answer to the objection that the calx is heavier than the 

 metal a fact which, as we have seen, was known to Boyle. " This 

 fact," says Stahl, " so far from damaging my theory, supports it. For 

 phlogiston, being lighter than air, tends to lift up the bodies it com- 

 bines with, so that they lose a part of their weight ; hence a body 

 which has parted with its phlogiston weighs more than before." The 

 phlogiston theory reigned for half a century amongst chemists, and 

 its history is an example of the manner in which a scientific theory 

 may be accepted as a simple and adequate explanation of a group of 

 facts, until further discoveries concerning allied facts require the 

 theory to be modified by additional hypotheses and speculative ex- 

 planations, until it becomes so involved in complications as to be 

 useless as a bond of union for the facts. We shall again refer to the 

 disputes to which the phlogiston theory gave rise towards the end of 

 the eighteenth century, when scarcely two chemists would be found 

 to give the same theoretical explanation of the facts of their science. 



The works of Stahl are curious in a literary sense from the strange 

 mixture of German with the Latin. Here is a translation of a passage : 



" Besides, by the above-mentioned alteration in metals, it must be 

 observed that they contain three principles or substances. i. a sub- 

 stance of almost superficial cohesion, which first goes off, that is to say, 

 the inflammable substance or phlogiston ; 2. a colouring substance 

 which is seen in the coloured glasses of these metals ; and finally : 

 3. a cruder substance, which is found particularly in the thicker 

 metals, iron and copper." The text of this passage runs thus: 



" Sonsten ist aus den angefiihrten alterationibus metallorum zu notiren 

 dass in den metallis imperfectis dreyerley substantia vorhanden sey : 

 i. eine quasi superficialis cohoesionis quae et ea propter omnia prima 

 abit scilicet substantia ' inflammabilis seu <j>\oyi arov ; 2. substantia 

 colorans, quae apparet in coloratis horum metallorum vitris, und end- 

 lich; 3. substantia crudior, und diese sonderlich in den crassioribus 

 metallis, Risen und Kupfer zufinden" 



The study of gases, the existence of which had been demonstrated 

 by Van Helmont and Boyle, was the foundation of the science of che- 

 mistry. The most valuable results were obtained from investigations on 

 the air, respiration, combustion, fermentation, irrespirable airs, gases in 

 mineral water, and similar subjects, which offered a hitherto un worked 

 mine of scientific truths. Most persons having any taste for experi- 

 mental science in the seventeenth century dabbled in chemistry, and 

 the store of facts began to accumulate rapidly. Sir Christopher Wren, 

 Dr. Hooke, Huyghens, and others, each contributed some experimental 

 truths to the growing science. A young English physician, named 

 JOHN MAYOW {1645 1679), published in 1674 treatises on nitre and 

 on respiration, in which he described experiments that are, perhaps, the 



