THE MOLECULAR COMPOSITION OF MATTER^ 77 



will throw out sparks and burst into flame. Priestley 

 was also the first to notice the exhilarating effect of 

 breathing pure oxygen, although he preceded the 

 experiment upon himself by trying the gas on two 

 mice. 



The experiments of Lavoisier extended over several 

 years. His final conclusion as to air was reached in 

 1777. It consists of a mixture of two gases, one 

 capable of supporting combustion and the other 

 incapable, oxygen and nitrogen, respectively. By 

 this time he had coordinated and extended the re- 

 searches of his contemporaries, reaching a conclusion 

 in accord with their experimental results but not always 

 with their theories, for many of them were phlogis- 

 tists. His demonstration of the fallacy of the phlogis- 

 ton theory occurred earlier (1772). He burned 

 phosphorus in a closed vessel and showed that when 

 all the phosphorus which could be made to burn had 

 been consumed, (1) about one fifth of the air had 

 disappeared (the oxygen) ; (2) the loss in weight of 

 the air was practically equal to the difference in weight 

 of the resultant white solid and the original phosphorus ; 

 and (3) the density of the residual ah* was now less 

 than that of the original ah-. An effective demonstra- 

 tion of the conservation of matter was thus made by 

 Lavoisier. The progress of the " science of the com- 

 position of substances," as Boyle had defined chemistry, 

 thereafter proceeded with great rapidity. 



The discovery of the chemical composition of the 

 atmosphere as one volume of oxygen to each four 

 volumes of atmospheric nitrogen 1 gave no immediate 

 1 Nitrogen and traces of some other gases. 



