84* SALT-MAKING. 



the vessel. Every one has noticed the force with 

 which the steam of water in a tea-kettle issues from 

 the spout, and may have seen the force of boiling 

 water drive off the cover of a saucepan ; and it is 

 said, and possibly it is true, that the discovery of 

 the steam-engine was owing to one or other of 

 these ; but when, as in boiling brine for salt, the 

 surface of the water is freely exposed to the air, 

 the heat and water go off together ; and if the 

 boiling were continued long enough, the water 

 would pass entirely into the atmosphere. Salt 

 does not pass so easily into vapour as water ; and, 

 therefore, as the water boils off in vapour, the re- 

 maining liquid becomes salter and salter, until 

 at last there is much more salt than the re- 

 maining water could keep dissolved if it were 

 cold. If the boiling were carried on too long, the 

 salt, together with the other matters in the water, 

 would begin to form a crust at the bottom, but 

 the salt-makers here " observed" the proper 

 strength to which the brine should be boiled; and 

 they stop the boiling and allow the water to cool, in 

 that state when there is not so much water as is 

 sufficient to overcome the tendency which the invi- 

 sible atoms of salt have to form themselves into 

 crystals, and so as the stronger power invariably acts 

 in nature, the salt crystallizes. The brine is thus 

 obtained by motion (it becomes brine by the ingre- 

 dients of water and salt, which are at the least 

 four in number, moving into a very intimate con- 

 nexion with each other) . The brine is warmed by 

 motion ; the surplus water is carried off by motion ; 

 the water is cooled by motion (the motion of the 

 heat out of it), and the salt is crystallized by mo- 



