40 A YEAR IN SCIENCE 



this temperature, but each has its own melting point. 

 For instance, alcohol melts at 130 C., mercury at 

 39.5C., zinc at 419C., copper at 1065C., and cast 

 iron at 1200C. 



The melting temperatures of some substances, espe- 

 cially gases, are so low that they have never been seen 

 in the solid state outside of the laboratory, or in the 

 liquid state except in laboratories where very low tem- 

 peratures can be artificially produced. 



The fact that the melting points of substances differ 

 greatly makes it possible to melt sugar in a glass vessel, 

 or glass in an iron vessel. Why? 



Some substances gradually soften and become pliable 

 before they melt. This fact is utilized in the molding 

 of glass or iron into different forms. 



Boiling 1 points. The temperature at which a liquid 

 becomes a gas is known as its boiling point. The boiling 

 point of a substance is also the temperature at which, 

 in a gaseous state, it condenses and again becomes a 

 liquid. For instance, water boils at 100 C. Steam also 

 condenses at this temperature. 



Liquids have their characteristic boiling points just 

 as solids have their characteristic melting points. The 

 boiling point of ether is 35C., of alcohol 78C., of 

 water 100C., of mercury 350C., of sulphur 448C., of 

 zinc 1040C., and of copper 2100C. 



Some substances boil at very low temperatures. 

 Most of those substances are never seen in the liquid 

 state, except in laboratories. They are known only in 



