OBJECTS.] INTRODUCTORY. 77 



dissolved, and the solution is called brine. 

 Moreover, the solution is said to bj saturated, for 

 if you put more salt in it will remain unchanged. 

 Water, in fact, will dissolve two-fifths of its weight 

 of salt, and no more. If the brine thus formed is put 

 into a wide dish, so that the water may evaporate ; or 

 if it is heated and the water boiled away ; as fast as the 

 water diminishes, a quantity of salt, equal to two-fifths 

 of the water which is converted into steam, returns to 

 the solid state and falls to the bottom of the vessel. 

 And when all the water is driven off, the salt which 

 remains will have exactly the weight, and all the other 

 properties which it had before it was dissolved by the 

 water. 



Thus, contact with water has had a very singular 

 effect upon the salt. It appears to have changed one 

 of the properties of the salt, namely, its solidity, 

 but to have left all the rest unaltered. We saw just 

 now that powdered ice does not mix with ice-cold 

 water, but that the fragments of ice remain solid. The 

 moment, however, that the temperature rises, the 

 cohesion, or sticking together of the molecules, 

 which is the characteristic of the solid state, comes to 

 an end ; they become loose and free to move, and they 

 mingle with the surrounding water. Or we may say 

 that the ties which held the molecules of the solid 

 together are dissolved, so that the solid water becomes 

 fluid. 



The resemblance of this process to the dissolving 

 of salt in water is so obvious that, in. common lan- 

 guage, it is often said that a lump of salt or of sugar 

 melts away in water ; but if you try to make salt 

 fluid by heat, you will have to expose it to a very high 



