30 TEE FORMS OF WATER IN 



particularly striking manner, and when properly fused 

 and solidified, self-built crystals of great size and beauty 

 are formed of this metal. 



87. If you dissolve saltpetre in water, and allow the 

 3olution to evaporate slowly, you may obtain large 

 crystals, for no portion of the salt is converted into 

 vapour. The water of our atmosphere is fresh though it 

 is derived from the salt sea. Sugar dissolved in water, 

 and permitted to evaporate, yields crystals of sugar- 

 candy. Alum readily crystallizes in the same way. 

 Flints dissolved, as they sometimes are in nature, and 

 permitted to crystallize, yield the prisms and pyramids 

 of rock crystal. Chalk dissolved and crystallized yields 

 Iceland spar. The diamond is crystallized carbon. All 

 our precious stones, the ruby, sapphire, beryl, topa^,, 

 emerald, are all examples of this crystallizing power. 



88. You have heard of the force of gravitation, and 

 you know that it consists of an attraction of every 

 particle of matter for every other particle. You know 

 that planets and moons are held in their orbits by this 

 attraction. But gravitation is a very simple affair com- 

 pared to the force, or rather forces, of crystallization. 

 For here the ultimate particles of matter, inconceivably 

 small as they are, show themselves possessed of attrac- 

 tive and repellent poles, by the mutual action of which 

 the shape and structure of the crystal are determined. 

 In the solid condition the attracting poles are rigidly 

 kicked together; but if sufficient heat be applied the 



