210 MODERN SCIENCE READER 



tion breaks up substances into their elements. He further 

 defined the distinction between a chemical compound and 

 a mixture ; he maintained that the properties of a chemical 

 compound are quite different from those of its components, 

 and that in a mixture each retained its characteristic prop- 

 erties practically unaffected. Above all, he earnestly 

 warned chemists against adopting hypotheses and general 

 theories a priori. Theories are necessary; but unless they 

 are generalizations cautiously made from observed facts, 

 they may be dangerously misleading. 



Boyle's views are now accepted universally. Had he 

 grasped and succeeded in spreading abroad one more idea 

 viz., the absolute necessity of quantitative investigation- 

 he would doubtless have become the founder of the science 

 of chemistry that is to say, with him would have com- 

 menced the epoch enlightened by truth and free from 

 fundamental errors. This he did not accomplish; nor was 

 it possible to accomplish it before the characteristics of 

 gaseous matter came to be known better than they were in 

 his day. And so it came about that chemists failed to 

 appreciate his great warning against hypotheses that are 

 not rigidly correlated with facts, and adopted a belief in 

 a fiery "phlogiston"; thus creating a period of darkness 

 that lasted a century. It must be remembered that the 

 important phenomena of what we now call oxidation en- 

 gaged the attention of chemists toward the end of the 

 seventeenth century and through the entire eighteenth 

 century. These phenomena were explained by the sup- 

 posed existence of ' ' phlogiston, ' ' a substance that may have 

 been first produced in the mind of some alchemist, but the 

 first clear reference to which, under the name of terra 

 pinquis, we find in the works of Becher (1635-82). Stahl 

 (1660-1734) named it phlogiston, endowed it with certain 

 imaginary properties, and used it as the basis of a doctrine 

 that was soon accepted throughout the civilized world. 



To give a clear and precise account of this, as of any 

 other erroneous doctrine, is a matter of considerable dif- 



