in THE BURNING OF METALS 29 



on a cupel, under a muffler, acquired one dram, six grains 

 and a quarter, increase of weight." 



" A piece of refined silver, being put upon a cupel under 

 a muffler, and kept there for an hour and a half, was 

 taken out, and weighed again ; and as before it weighed 

 three drams, thirty-two grains and a quarter, it now weighed 

 in the same scales, three drams, thirty-four grains and a 

 quarter" (Works, 1725, II. 389-390). 



Boyle calcines tin in sealed flasks. Although Boyle was 

 convinced that metals really gained in weight when burnt, 

 he regarded these experiments as unsatisfactory because the 

 metals were exposed to the smoke and dust of the furnace. 

 To get over this difficulty he heated the metals between 

 two crucibles cemented together with clay, and finally (in 

 the case of the more fusible metals) made use of glass 

 flasks, the necks of which were loosely stoppered, drawn 

 out to a fine point, or sealed up altogether. Boyle's experi- 

 ments on the calcination of tin in sealed flasks are of special 

 interest as having provided the basis for Lavoisier's experi- 

 ments on the same subject. 



"To prevent all suspicion of any increase of weight, in 

 the metals, arising from smoke, or saline particles, getting 

 in at the mouth of the vessel, I made the experiment in 

 glasses, hermetically sealed, as follows. Eight ounces of 

 good tin, carefully weighed, we hermetically sealed up in a 

 new, small retort, with a long neck, by which it was held in 

 the hand near a charcoal fire, that kept the metal in fusion ; 

 being now and then shaken for almost half an hour ; in 

 which time, it seemed to have acquired, on the surface, such 

 a dark colour, as argued a beginning calcination ; and it 

 both emitted fumes that played up and down, and also, 

 afforded two or three drops of liquor, in the neck of the 

 retort. The glass was, at length, laid on quick coals, 

 where the metal continued above a quarter of an hour longer 

 in fusion ; but, before the time was come, that I intended, 

 to suffer it to cool, in order to its removal, it suddenly broke 

 into a great multitude of pieces, and with a noise, like the 

 report of a gun." 



