4 SMITH'S INTERMEDIATE CHEMISTRY 



the properties of one, or of more than one substance. He then 

 describes it by naming the substances he finds in it. 



Another Illustration. This view-point is peculiar to the 

 chemist. Each art or science has its own view-point its own 

 way of thinking about a given object. By the geologist, a piece 

 of granite is at once thought of as belonging to the older rocks of 

 the earth, and the geologist considers when it was formed and how 

 it was formed (namely, by solidification of a molten mass), 

 To the builder, it is a very hard stone, expensive to cut and pol- 

 ish, but very ornamental, and very durable. How and when 

 it was formed does not make any difference to the builder. 



To the chemist, as a chemist, on the other hand, the expense 

 of cutting granite, and its ornamental character, are of no interest. 

 Instead, the chemist notices at once that it is spotted, and, upon 

 examining it closely, he observes that it appears to be a mixture. 

 He breaks up a portion, and studies the properties of the fragments. 

 Some are transparent like glass, are very hard, and in fact are in 

 all respects like quartz or rock crystal (Fig. 3). All specimens 

 of rock crystal, from whatever source, are alike in properties, 



and quartz is, therefore, a distinct 

 substance or species of matter. Again, 

 certain of the particles in granite are 

 dark, and with a penknife can be 

 easily split into transparent leaves, 

 thinner than paper. These fragments 

 are in all respects like mica (sheets of 

 which, under the name of " isinglass," are used to close the win- 

 dows of stoves), which is another substance (Fig. 4) well-known to 

 the chemist. Still others of the fragments are less transparent 

 than the quartz and less hard. They can be split, but with 

 much greater difficulty than the mica. They are crystals,* 



* Crystals are natural forms of a geometrical nature, assumed by solid sub- 

 stances (p. 94). 



