62 Chemistry. [Lecture 26. 



when it is close and compact ; it is called flowers, 

 when its texture is loose like soot. 



Animal and vegetable substances are composed 

 of various ingredients, which may be separated 

 by the application of heat. But heat operates 

 upon them in a different manner from what it 

 does on other substances. If a piece of flesh is 

 exposed to heat, it is not like iron expanded, but 

 on the contrary, is contracted ; for the humid 

 parts fly off, and leave only the fixed or denser 

 parts behind. 



Heat applied to animal substances does not 

 convert them into a vapour that may be con- 

 densed into any substance of the same kind, but 

 into oil, water, charcoal, and some saline sub- 

 stances. When the volatile parts are evaporated, 

 the remainder has a different arrangement from 

 what it had before. 



It may seem rash to assert that heat has a 

 power of bringing into fusion and volatilization 

 all bodies without exception, as we have not suf- 

 ficient data or experiments to render this opi- 

 nion absolutely certain ; for all those earthy sub- 

 stances that have been rendered fluid have not as 

 yet been converted into vapour, and there are 

 some earthy substances that have not even been 

 brought into fusion. 



Some metals, especially gold and silver, were 

 once thought to be absolutely fixed. Boyle 

 took a small quantity of each, and exposed them 

 for two months to a glass-house furnace, and at 



