VOLATILE LIQUIDS. 



The liquid consequently becomes very cold 

 so cold that about one-third of it is frozen 

 into a powdery solid, like snow, and is collected 

 in a thin circular layer on the cloth, the clear 

 gas having filtered through. 



The liquid has boiled itself into a frozen solid! 



This solid carbonic acid is extremely cold. 

 It has 143 degrees of frost on the Fahrenheit 

 scale. Its extreme cold can readily be felt by 

 pressing the ringer upon it. More of it can be 

 collected by piercing two or three capsules on 

 the same surface. If a quantity of the size of a 

 pea be forcibly compressed between the finger 

 and thumb the excessive cold will cause mor- 

 tification of the skin. 



It is very volatile, and in a few minutes 

 will all disappear by volatilisation, without 

 melting. Any appearance of moisture is from 

 moisture in the air, condensed by the cold 

 surface left behind. 



2. Ice as a Heating Agent. 



Different liquids boil at different tempera- 

 tures. Sulphuric acid or mercury must be 

 made much hotter than boiling water before 

 they will boil. Alcohol, ether, and chloroform, 

 on the other hand, will boil at a much lower tem- 

 perature than water ; and water itself, as we 

 have seen, will boil at a lower temperature when 

 there is less pressure upon it. This can, be 



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