Chemical Effects of Caloric, $c. 75 



will be almost impossible to confine it, and it 

 will often burst the vessel with a loud explosion. 

 This effect of the force of vapour is sufficiently 

 exemplified by the small pieces of glass called 

 candle-balls, which burst by the expansion of 

 the vapour. This great expansion of the vapour 

 is the true cause of the danger of throwing water 

 into boiling oils or melted metals, especially 

 brass or copper. The water being a heavier 

 fluid than the oil falls to the bottom, where it is 

 immediately converted into vapour, and causes 

 a violent ebullition. A small quantity of hu- 

 midity when mixed with hot metals, will be con- 

 verted into vapour with such rapidity as to pro- 

 duce a more violent explosion than gunpowder. 

 Hence the danger of casting copper or iron ves- 

 sels ; for, if the fluid metal meets with the least 

 moisture in its passage from the furnace to the 

 mould, the watery particles are instantly ex- 

 panded, and throw the burning metal to a con- 

 siderable distance. Vapour, when condensed, 

 resumes its former state ; and upon these prin- 

 ciples, viz. the elasticity and condensibility of 

 vapour, depends the construction of the steam- 

 engine, as was formerly explained. 



To compare the weight of steam or vapour 

 with that of water, place a flask with a small quan- 

 tity of water in it before the fire ; the moment the 

 whole of the water is converted into vapour, 

 close the vessel, and it will then be filled with 

 steam. Weigh the vessel thus filled with steam, 



E2 



