The Evolution of Chemistry. 127 



of this innovation changed somewhat their mental attitude, 

 leading them to perceive that, instead of mere qualities flit- 

 ting from thing to thing, material transfers had some part 

 in the matter. About this time chemistry was known as 

 the spagyric art, or art of synthesis and analysis. The 

 chemical behavior of sour bodies or acids to acrid bodies or 

 alkalies was shown by Sylvius early in the seventeenth cen- 

 tury. This at once awakened the idea of chemical attraction, 

 and at a little later date that of elective affinities. Geoffrey 

 tells us that " in all cases where two substances that have 

 any disposition to combine are united, if there approaches 

 them a third, which has more affinity with one of the two, 

 this one unites with the third and lets go the other." 



Here it is to be noted that abstract qualities are not re- 

 ferred to, and only the behavior of substances considered. 

 About this time Boyle severely criticised the three-element 

 theory, and Beckner and Stahl introduced a substitute for 

 sulphur that dethroned it. They taught that all inflammable 

 substances contained within them an element the escape of 

 which was the cause of fire. This hypothetic element was 

 called phlogiston. Bodies that would not burn were thought 

 to be dephlogisticated. In this theory we hear the last 

 echo of metaphysical chemistry as a dominant system. 

 Phlogiston was the logical and lineal descendant of the 

 god of fire. To destroy this was to subvert all ancient pro- 

 cesses of reasoning and compel men to gather their facts 

 together and begin again to build de novo. Being the 

 masterpiece of centuries of thought, it was not to be ex- 

 pected that it would die easily. The best minds were wed- 

 ded to it, and the very men who forged the weapons for its 

 destruction refused to accept the results of their own work. 

 In 1755 a young man named Black, then twenty-four years 

 of age, startled the scientific world by a graduation thesis, 

 the topic of which was something he called "fixed air." 

 At a little later date this gas was known as carbonic acid. 

 "When writing this thesis it occurred to him that it would 

 not be a bad idea to weigh the materials with which he was 

 dealing experimentally to gain his data. No chemist had 

 ever thought of doing such a thing before. It had invari- 

 ably been taken for granted that as qualities, not substances, 

 were altered, it made little or no difference whether creation 

 and annihilation were incessantly going on or not. He at 

 once proceeded to act by the suggestion. In the pivot of 

 that pair of Scotch scales we find the turning point be- 



