6 SMITH'S INTERMEDIATE CHEMISTRY 



The Law of Component Substances. Every material 

 consists of certain substances, each of which has a definite set 

 of specific properties. In terms of these properties the material 

 can be described. This is the first and simplest law of chemistry, 



and at the same time the most fundamental. 



Mixtures and Impurities. A material containing more 

 than one substance is called a mixture. The characteristic of a 

 mixture is that each of the substances present, although mixed 

 with the others, possesses exactly the same properties as if it were 

 present alone. No one of the ingredients affects any other 

 ingredient, or alters any of its properties. Granite and flour 

 are typical mixtures. 



When a specimen is composed mainly of one substance, and 

 contains only minute amounts of one or more other substances, 

 it is frequently spoken of as a specimen of the main substance 

 containing certain specified substances as impurities. To be 

 called an impurity, the foreign matter need not be dirty or offen- 

 sive. Thus, common salt usually contains a little magnesium 

 chloride, a white crystalline solid, as an impurity, and it is this 

 impurity which becomes damp in wet weather. Again, com- 

 pounds of lime and magnesium are common impurities in drink- 

 ing water. 



Component. The ingredients of a mixture are called the 

 components (Latin, put with), because they are simply placed 

 together, without change, and can be separated without change. 



Other Specific Properties. Beside the specific properties 

 which happen to have occurred in these illustrations, there are 

 others which are constantly found useful by the chemist. Thus, 

 in the case of solids, besides the hardness and crystalline form, he 

 gives special attention to the temperature at which the substance 

 melts (the melting-point), the specific gravity or density (weight 



