CHEMISTRY AND ITS DEVELOPMENT 211 



ficulty. For when ingenious men are dominated by error, 

 they usually mold it in a variety of forms to give it the 

 appearance of truth and render it consistent with itself. 

 The phlogistonians handled their hypothesis with much 

 dexterity. Yet their thought, lacking the character of quan- 

 titative precision, was weak; for quantitative conceptions, 

 while already mastered by the physicists, were still in a 

 state of confusion in the minds of the chemists. Distin- 

 guishing clearly between the weight of bodies and their 

 specific gravity, we have no difficulty in understanding 

 that although water vapor is lighter than air, its addition 

 to a given body must increase the weight of the latter, 

 because water, whether liquid or vaporized, has weight. 

 Stahl believed that the conversion of a "calx" (i.e. a metal- 

 lic oxide) into a metal was caused by the addition of 

 phlogiston. He knew that the conversion was accompanied 

 by the diminution of weight; but from this fact he only 

 deduced that phlogiston must be ' * lighter than air, ' ' failing 

 to grasp that such an addition may make a bod}' lighter^ 

 in the sense of producing one of lower specific gravity, 

 but necessarily make it heavier in the sense of increasing 

 its absolute weight. It is more probable, however, that 

 Stahl understood this in a general way, but thought that 

 the metals had a lower specific gravity than their calces. 

 At least, Juncker, a pupil of Stahl's, asserts this about 

 metals and calces as a matter of fact, although Boyle had 

 long since shown experimentally that the specific gravity 

 of metals is really higher than that of their calces. Much 

 more extraordinary is the conception that we find in the 

 writings of Guyton de Morveau, Macquer and others, who 

 taught that phlogiston had less than no weight! Stahl con- 

 ceived of phlogiston as a fiery principle, "materia aut prin- 

 cipium ignis, -non ipsi ignis.' 9 Seeing that charcoal burns 

 up completely, and is capable of producing metals by 

 adding itself, as he thought, to their calces, he considered 

 charcoal as made up almost entirely of phlogiston. Caven- 

 dish knowing that "inflammable air" is given off when 



