48 FIRST YEAR COURSE IN GENERAL SCIENCE 



having characteristics different from those of the elements 

 which compose it. Sugar, salt, and water are compounds. 



Considering that the eighty known elements may be com- 

 bined in groups of two or more, and in different proportions, 

 it is evident that many thousands of compounds may be 

 formed from them. 



If two elements, as mercury and iodine, unite to form a 

 new and different substance, or if a substance separates into 

 the parts of which it is composed and two or more elements 

 result, such a change is a chemical change. No one of the 

 resulting parts is like the original. 



43. Mixtures. Nearly everything that we eat or drink, 

 the air we breathe, the substances of which our bodies are 

 made, the paper and ink with which we write, each 

 of these things is either a compound or a mixture. With the 

 exception of carbon, sulphur, and the metals, we rarely 

 see or use anything that is an element. A mixture is 

 formed when two or more substances (elements or com- 

 pounds) are brought so closely together as to seem one 

 substance and yet retain their original qualities. Sirup is a 

 mixture of sugar and water; it is still sweet and a liquid. 

 Air is a mixture of nitrogen, oxygen, and other gases; 

 tincture of iodine is a mixture of alcohol and iodine; brine 

 is a mixture of salt and water. It is often difficult for any 

 one but a chemist to distinguish between mixtures and 

 compounds. 



The dissolving of salt or sugar in water is an example of 

 a physical change because no new substance is formed. The 

 resulting substance is liquid, as water is. It has a salt or a 

 sweet taste, as salt or sugar has. Each substance could be 

 recognized by a description of the mixture. The same salt 

 or sugar could be procured in the solid form by allowing 

 the water to evaporate. 



44. Properties. The word property, as it is used in 

 science, means a quality or characteristic possessed by a 



