20 HISTORY OF CHEMISTRY. [LECTURE II. 



there is, according to him, very little phlogiston. During com- 

 bustion, the phlogiston of the combustible substance escapes, 

 along with this saline substance from the oxygen, in the form 

 of heat and light ; the other constituent of the combustible sub- 

 stance the metallic calx, for instance remains behind, united 

 to the water of the oxygen. With Scheele, hydrogen is almost 

 pure phlogiston, which, however, contains a small quantity of 

 that hypothetical substance (matter of heat) which is also 

 present in oxygen. When hydrogen is burned with oxygen, the 

 water of the latter separates, and the matter of heat from the 

 oxygen unites with the hydrogen the compound of phlogiston 

 with little of the matter of heat and produces heat and light. 

 Thus it was only necessary to add some of that hypothetical 

 substance to hydrogen in order to convert it into heat or light. 



Scheele's views are at variance with all the relations by 

 weight, about which he troubled himself very little. In 

 accordance with his views, the metallic calx, for instance, 

 should weigh less than the metal plus the oxygen consumed ; 

 since the phlogiston of the former escapes, in combination 

 with the matter of heat from the latter, as heat and light. 

 The assumption of a ponderable matter of heat, which plays a 

 great part in his arguments, was at variance with the earlier 

 experiments of Boerhave (compare p. 8), so that Scheele, in 

 his theoretical views, came nearer to those who would retain 

 Stahl's doctrine at any cost, than to those who desired an 

 explanation of the observed facts, free from preconceived ideas. 

 I leave these, however, and I do so all the more willingly, 

 because I now wish to turn to the ideas and observations of 

 Lavoisier, which are accessible and comprehensible to every 

 one, and constitute the basis of the chemistry of to-day. 



It is not requisite that I should enumerate and describe all 

 the researches of this accomplished investigator ; this would 

 exceed the claims which any one could make, in such a his- 

 torical sketch as I intend to give. On the other hand, the im- 

 portance of the philosopher with whom I have now to deal, 

 requires that he should be treated of apart from his con- 

 temporaries. 



