792 EVAPORATION. 



exactly 0-91674; 12 CC of ice weigh 11 grammes, and 

 give ll cc of water when melted. It follows that water 

 which freezes increases its volume by T y. This increase 

 of volume in the formation of ice takes place with great 

 force so as to produce powerful mechanical effects, of 

 which, in winter, the bursting of water-pipes and the 

 breaking of jugs containing water are familiar examples. 



If a battle filled with water and tightly corked be exposed to the 

 cold on a frosty day, the cork is often lifted by the expanding 

 water, bat as the liquid in the neck soon freezes so as no longer to 

 allow a further expansion in that direction, the flask soon bursts. 



A closed glass vessel, prepared in the same manner as the little 

 float, fig. 385, but filled up to the narrow neck with water, may be 

 burst by placing it for a few minutes in a freezing mixture made of 

 600 grammes of pounded ice and 200 grammes of salt, adding no 

 water, and preparing the mixture in a flat tin basin, as vessels of 

 glass or china are liable to be broken by the explosion. The little 

 glass vessel is generally split into numerous long splinters, but 

 sometimes only the point is cracked off. 



56. Evaporation, Ebullition, and Condensation of 

 Vapour. Moist bodies exposed to the air become 

 gradually dry. The water which was in or upon them 

 passes into the gaseous state and disappears by diffusing 

 itself into the surrounding air ; it is said to ' evaporate/ 

 Other liquids behave in this respect like water. Some 

 liquids, for instance mercury, evaporate extremely 

 slowly; others, for example ether and disulphide of 

 carbon, evaporate much more rapidly than water. In 

 all liquids the rate at which evaporation proceeds 

 becomes higher if the temperature rises. 



At a particular temperature the formation of vapour 

 takes place with greater rapidity than at lower tempera- 

 tures, and large bubbles are disengaged from the liquid 

 which produce a violent agitation throughout its mass. 



