in THE BURNING OF METALS 35 



were carried out with a full knowledge of the work of his 

 predecessors, and were modelled largely upon the work of 

 Mayow and Boyle. 



By means of a burning-glass 33 inches in diameter, 

 Lavoisier calcined lead and tin in air enclosed in a glass 

 vessel inverted over water or mercury 1 (Fig. 15), and found 

 that " the volume of air diminished by about a twentieth 

 as a result of the calcination, and that the weight of the 

 metal is increased by an amount almost equal to that of 

 the air destroyed or absorbed." He concluded " that a 

 portion of the air .... combined with the metals during 

 their calcination, and that the increase in weight of the 

 metallic calces was due to this cause " (" Memoir on the 

 Calcination of Tin in Closed Vessels," 1774, Works, II. 105.) 

 Thus in contrast to the current view that 

 Metal = Calx + Phlogiston 

 Lavoisier reverted to the suggestion of Jean Rey that 



Metal + Air = Calx, 



the metal being regarded as a simple substance and the 

 calx as a compound. 



Lavoisier calcines tin in a sealed flask. In order to test 

 the view that the gain in weight of metals during calcination 

 was due to the absorption of air, Lavoisier, in 1774, repeated 

 Boyle's experiment of heating lead and tin in sealed glass 

 vessels. But, unlike Boyle, he carried out the critical experi- 

 ment of weighing the sealed retort both before and after 

 heating. In making these experiments Lavoisier had the 

 advantage of using a balance, more sensitive than any that 

 had been constructed previously, with which he was able to 

 detect changes in weight of yj^ of a grain. 



The experiment was carried out as follows : Eight ounces 

 of tin were weighed into a retort of 43 cubic inches capacity, 

 heated to drive out part of the air, sealed up and again 

 weighed. The tin was then heated in the sealed retort for 



1 Compare Priestley, Experiments on Air, I. 136. 



D 2 



