512 SPECIAL METHODS OF DISCOVERY. 



is phlogisticated ; ' i.e. burned. Lavoisier was engaged at 

 the same time on the same question, and made a similai 

 discovery a few months later. 



The discovery that metals increase in weight by oxi- 

 dation was made by Lavoisier in the following manner 

 whilst testing the theory of phlogiston : ' He put a 

 quantity of tin (about half a pound) into a glass retort 

 sometimes of a larger and sometimes of a smaller size, anc 

 then drew out the beak into a capillary tube. The retort 

 was now placed upon the sand-bath, and heated till the tin 

 just melted. The extremity of the capillary beak of the 

 retort was now placed so as to seal it hermetically. The 

 object of this heating was to prevent the retort from 

 bursting by the expansion of the air during the process 

 The retort, with its contents, was now carefully weighed 

 and the weight noted. It was put again on the sand-bath 

 and kept melted till the process of calcination refused to 

 advance any further. He observed, that if the retort was 

 small, the calcination always stopped sooner than it did ii 

 the retort was large. Or, in other words, the quantity ol 

 tin calcined was always proportional to the size of the 

 retort. After the process was finished, the retort (stil! 

 hermetically sealed) was again weighed, and was always 

 found to have the same weight exactly as at first. The 

 beak of the retort was now broken off, and a quantity oJ 

 air entered with a hissing noise. The increase of weight 

 was now noted ; it was obviously owing to the air that had 

 rushed in. The wefght of air that had at first been driven 

 out by the fusion of the tin had been noted, and it was 

 now found that a considerably greater quantity had entered 

 than had been driven out at first, in some experiments, 

 as much as 10*06 grains, in others 9*87 grains, and in 

 some less than this, when the size of the retort was small. 

 The tin in the retort was mostly unaltered, but a portion 



