1 8 HISTORY OF CHEMISTRY. [LECTURE II. 



it. 5 But in order that this may take place the phlogiston must 

 find another substance with which to unite. Combustion is 

 possible in air ; therefore air can take up phlogiston, but that 

 only to a certain extent, for after some time it becomes incap- 

 able of supporting combustion any longer. It is then saturated 

 with phlogiston. Substances burn in the oxygen gas discovered 

 by Priestley better than they do in air : it is dephlogisticated air 

 (a name which Priestley proposes for the new substance) or air 

 deprived of phlogiston, and it is thus better fitted for taking up 

 phlogiston than ordinary air is. The nitrogen, on the other 

 hand, which remains behind after the oxygen of the air has 

 been absorbed (and with regard to which Priestley is aware that 

 it neither supports combustion nor respiration) is air saturated 

 with phlogiston, or, phlogisticated air. With Priestley the exist- 

 ence of oxygen was no argument against the assumption of 

 phlogiston, which he defended till the end of his life. Thus we 

 find him at the beginning of the present century, when the 

 majority of chemists had given up the phlogiston theory, 

 addressing letters to the French Academy from America 

 (whither he had withdrawn, chiefly on account of his political 

 opinions), in which he requests refutation of his views. 6 This 

 was not difficult to give, and although it was refused him by 

 the learned French Society, I must not omit to point out what 

 is fallacious in his mode of regarding the matter. 



" When a substance burns in air, the latter becomes phlo- 

 gisticated " if we burn phosphorus, we obtain phosphoric acid 

 (or phosphorous acid), while nitrogen, the phlogisticated air, 

 remains behind. But if we burn a candle, or coal, we obtain a 

 mixture (consisting of nitrogen and carbonic anhydride), part 

 of which can be absorbed by means of alkali, thus exhibiting a 

 phlogisticated air, possessed of properties different from those 

 of the preceding one. If we burn phosphorus in dephlogisticated 

 air, nothing at all remains behind the phlogisticated air van- 

 ishes. The contradictions to which Priestley's system leads, 

 become manifest when it is applied to the facts known even at 



5 Kopp, Geschichte. I, 242. 6 Dumas, Le9ons. 115. Priestley, The 

 Doctrine, etc. x. and xii. 



