WATER. 



A cubic inch of water at 62, Bar. 30 inches, weighs in air 

 252.458 grains. The imperial gallon has been defined to con- 

 tain 10 pounds avoirdupois (70,000 grains) of distilled water at 

 that temperature and pressure. Its capacity is therefore 277.] 9 

 cubic inches. The specific gravity of water at 60 is 1, being 

 the unit to which the densities of all other liquids and solids 

 are conveniently referred; it is 815 times heavier than air at 

 that temperature. 



In its chemical relations water is eminently a neutral body. 

 Its range of affinity is exceedingly extensive, water forming 

 definite compounds, to all of which the name hydrate is applied, 

 with both acids and alkalies, with a large proportion of the salts, 

 and indeed with most bodies containing oxygen. It is also 

 the most general of all solvents. Gay-Lussac has observed 

 that the solution of a salt is uniformly attended with the pro- 

 duction of cold, whether the salt be anhydrous or hydra ted, 

 and that on the contrary, the formation of a definite hydrate 

 is always attended with heat : a circumstance which indicates 

 an essential difference between solution, and chemical com- 

 bination*. Even the dilution of strong solutions of some salts, 

 such as those of ammonia, occasions a fall of temperature. 

 The solvent power of water for most bodies increases with its 

 temperature. Thus at 57 water dissolves one fourth of its 

 weight of nitre, at 92 one half, at 131 an equal weight, and 

 at 212 twice its weight of that salt. Solutions of such salts, 

 saturated at a high temperature, deposit crystals on cooling. 

 But the crystallization of some saturated solutions is often 

 suspended for a time, in a remarkable manner, and afterwards 

 determined by slight causes. Thus, if three pounds of crys- 

 tallized sulphate of soda be dissolved in two pounds of water, 

 with the assistance of heat, and the solution be filtered while 

 hot, through paper, to remove foreign solid particles, and then 

 set aside in a glass matrass, with a few drops of oil on its 

 surface, it may become perfectly cold without crystallization 

 occurring. Violent agitation even may not cause it to crystal- 

 lize. But when any solid body, such as the point of a glass 

 rod, or a grain of salt, is introduced into the solution, crystals 

 immediately begin to form about the solid nucleus, and shoot 

 out in all directions through the liquid. The solubility of many 



* An. de Ch. et de Phys, t. 70 p. 407. See also page 180 of this work. 



