40 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



ordinary air must contain some phlogiston, and that in this 

 new gas he had, for the first time, obtained air free from 

 phlogiston. He therefore described it as DEPHLOGISTICATED 

 AIR, and attributed its superior power of supporting com- 

 bustion, to the fact that it was capable of receiving more 

 phlogiston from burning substances, and could therefore 

 maintain a flame for a longer period than ordinary air. 



Lavoisier makes quantitative experiments on the 

 calcination of mercury. In October of the same year 

 Priestley, when on a visit to Paris, informed Lavoisier of 

 his experiments. Lavoisier concluded that the new gas 

 was the active part of the air which he had tried without 

 success to separate. In November, 1774, he repeated 

 Priestley's experiments, and in the spring of the following 

 year read before the Academy of Sciences at Paris a 

 memoir " On the Nature of the Principle which Combines 

 with the Metals during their Calcination and Increases 

 their Weight" (Works, II. 122). In this memoir he 

 described as VITAL AIR or EMINENTLY RESPIRABLE AIR the 

 gas obtained by heating the red calx of mercury, and 

 confirmed Priestley's observations as to its properties, but 

 without making any reference to the source from which 

 he had obtained his first information as to the behaviour of 

 the calx. 



In his " Elementary Treatise on Chemistry," published 

 in 1789, Lavoisier described a series of experiments on the 

 calcination of mercury (Works, I. 35-38) which display to 

 the full his genius for exact and careful measurements. In 

 order to study the part that air played in the formation of 

 the red calx, he placed four ounces of pure mercury in a 

 retort, the neck of which was bent so that it passed 

 up into a bell-jar of air inverted over mercury (Fig. 16). 

 The total volume of air thus enclosed in the retort and the 

 bell-jar amounted to 50 cubic inches. He then heated the 

 retort, and observed the formation of a red scale on the 



