CH. in THE BURNING OF METALS 27 



for the space of six hours with continual agitation and 

 without adding anything to it, he recovered two pounds 

 thirteen ounces of a white calx ; which filled him with 

 amazement, and with a desire to know whence the seven 

 ounces of surplus had come " (A. C. R. XL 36). 



It had been suggested that the gain in weight was due 

 to soot or vapour from the furnace condensing on the tin, 

 or to the disintegration of the iron vessel ; Rey showed 

 that these explanations were unlikely, and concluded (on 

 the basis of argument rather than of experiment) 



" That this increase in weight comes from the air, which 

 in the vessel has been rendered denser, heavier, and in some 

 measure adhesive, by the vehement and long-continued heat 

 of the furnace : which air mixes with the calx (frequent 

 agitation aiding) and becomes attached to its most minute 

 particles : not otherwise than water makes heavier sand 

 which you throw into it and agitate, by moistening it and 

 adhering to the smallest of its grains " (A. C. R. XL 36). 



Rey supported his argument by quoting an experiment 

 of Hamerus Poppius, who had calcined a cone of anti- 

 mony on a marble slab by means of a burning mirror, 

 and had found the weight to be augmented instead of 

 diminished, in spite of the copious exhalation of vapours and 

 fumes (A. C. R. XL 49) ; in this case at least, the gain in 

 weight could not be attributed to contamination of the metal 

 by the furnace or vessel, and must surely be due to the 

 condensation of air. A similar explanation was given in 

 the case of lead, of which it had been recorded that " it is a 

 remarkable thing that lead on calcination increases in weight 

 by eight or ten pounds per cent " (A. C. R. XL 41). 



Robert Boyle (1673) confirms Key's statement that 

 metals gain in weight on calcination. Jean Rey himself 

 does not appear to have made any experiments on the gain 

 in weight of tin and lead. But the fact that metals gain in 

 weight when calcined was confirmed forty-three years later 



