60 Chemistry. [Lecture 26. 



mixed with the water; but Margraaff proved 

 that snow is in fact composed of the purest water. 



Reamur observes, that melted cast iron, in 

 passing from a hot to a cold state, expands. 

 This effect is more sensible in this than in any 

 other of the metals, on account of its platey tex,- 

 ture. He found also that cast iron thrown 

 among some of the same metal in a melted state 

 swims upon the top. In this case of immediate 

 expansion upon congealing, the iron seems to 

 agree with water. But they differ in this, that 

 the iron never expands by cold afterwards, 

 whereas the ice, being exposed to greater degrees 

 of cold, becomes still more bulky ; the solid parts 

 not being so closely connected form a particular 

 arrangement, which renders the whole mass spe- 

 cifically lighter than before. 



Denser bodies for the most part expand less 

 than rarer ; but this I observed is not an inva- 

 riable rule, for metals expand more than glass 

 or stones. The expansion of metals was found 

 to be a great obstruction to the regular going of 

 clocks, but is obviated now by the ingenious con- 

 trivance of making use of two different metals, 

 which do not expand equally, in constructing the 

 pendulums. 



Of the three classes of bodies which compose 

 the universe, solid bodies suffer the least expan- 

 sion from the presence of caloric. Liquids are 

 more expansible than solids ; and aeriform fluids 

 are most expansible of all. By the accurate ex- 



