94-(64) PHYSIOLOGICAL SIGNIFICANCE OF VITAL FORCE. 



it was that the analytic method became more accurate. 

 Black, with the balance, demonstrated that the ignition 

 of the metals, magnesium and calcium, gave no evidence 

 that a ponderable "caloric" entered into them, but, to the 

 contrary, a peculiar "fixed air" was expelled from them, 

 which rendered them lighter than before they were burnt. 



The foundation of quantitative chemistry was thus 

 laid, and the existence of ' ' imponderable ' ' agents in na- 

 ture questioned. The discovery of " dephlogisticated 

 air" by Priestley; the investigation of gases by Caven 

 dish ; of heat and lire by Scheel ; and of insoluble mine- 

 rals by Bergman — by means of the blow-pipe — were im- 

 portant additions to chemical knowledge, and enabled 

 Lavoisier to generalize the facts already discovered. He 

 announced a new theory of combustion, and, by question- 

 ing the existence of phlogiston, and showing that "prin- 

 ciples should not be assumed where they could not be 

 detected," revolutionized chemistry, and gave it anew 

 impulse which has been quickened by every discovery 

 since made. 



Analysis of inorganic bodies increased, new facts accu- 

 mulated and new interpretations of phenomena were 

 given, until the atomic theory, first suggested by Dalton in 

 L804, was promulgated under the great generalization 

 known as the law of Avogadro or Ampere, which makes 

 "equal volumes of all substances, when in the state of 

 gas, and under like conditions, contain the same num- 

 ber of molecules.*' This was the birth of modern chem- 

 istry, and though it received attention when first enunci- 

 ated in 1811, its far reaching principles of truth were 

 neither fully understood nor accepted for half a century 

 afterwards. 



Chemistry, free from the errors of the past, now seeks 

 to discover in the organic world, the relations of different 

 substances, as it has sought to know their relations in 

 inorganic nature, and already the evidence is prophetic 

 of wonderful results. 



in physical philosophy, "Stahlism" received its mor- 

 tal wound at the (dose of the last century, by the experi- 

 ments of Rumford and Davy, which negated the theory 

 of "caloric" and demonstrated heat to be a "mode of 

 motion." 



