Chemical Effects of Caloric, $c. 77 



and well luted : when the w r ater is so hot as to 

 send off vapour, its escape is prevented by mean 

 of a weight and lever across the lid, which con- 

 fine it in proportion to the increased pressure of 

 the vapour. The water by these means acquires 

 a degree of heat, which Muschenbroek says he 

 found sufficient to melt lead or tin. Bones have 

 by these means been totally dissolved in water, 

 and reduced to their constituent parts, nothing 

 remaining but earth or ashes, which may be 

 easily crumbled between the fingers. 



As the vaporific point is always the same 

 under the same pressure, we may consider it as 

 always the same in the open air ; at least it does 

 not vary more than three degrees. It is a mat- 

 ter of curiosity to examine the difference of the 

 vaporific point of any liquor under the exhausted 

 receiver, and when exposed to the pressure of 

 the atmosphere. It is found that water boils in 

 vacuo at ninety degrees. 



When a single drop of water is heated to its 

 vaporific point it immediately becomes vapour ; 

 but if the quantity is more considerable, the 

 phenomenon will be varied. For, if a quantity 

 of water is thrown into an iron vessel heated 

 red-hot, it will seem to run about the vessel like 

 quicksilver, but without touching the bottom or 

 sides of the vessel. The reason is, the water 

 nearest the bottom and sides is converted into 

 vapour, which prevents the water coming into 

 contact with the vessel. This is the reason, too, 



