62 PRINCIPLES OF CHEMISTRY. 



When the number of elements and the number of atoms in- 

 crease in the molecule, the .names become in most cases more 

 complicated. The rules applied to the formation of such com- 

 plicated names will be spoken of later. 



How to study chemistry. In studying chemistry, the student 

 is advised to impress upon his memory five points regarding 

 every important element or compound. These points are: 



1. Occurrence in nature. (Whether in free or combined state; 

 whether in the air, water, or solid part of our earth.) 



2. Mode of preparation by artificial means. 



3. Physical properties. (State of aggregation and influence of 

 heat upon it; color, odor, taste, solubility, etc.) 



4. Chemical properties. (Atomic and molecular weight; valence; 

 amount of attraction towards other elements or compounds; acid, 

 alkaline, or neutral reaction; reactions by which it may be rec- 

 ognized and distinguished from other substances.) 



5. Application and use made of it in every-day life, in the arts, 

 manufactures, or medicine. 



Of the most important elements and compounds, the history 

 of their discovery, and, occasionally, some special points of in- 

 terest, should also be noticed. 



All students having the facilities for working in a chemical 

 laboratory are strongly advised to make all those experiments 

 and reactions which will be mentioned in connection with the 

 different substances to be considered in this book. 



QUESTIONS. 



81. Why are not all the elements of equal importance? 



82. State the physical and chemical properties of metals. 



83. How are metals distinguished from non-metals ? 



84. What relation often exists between the atomic weights of ele- 

 ments belonging to the same group ? 



85. Explain the term allotropic modification. 



86. Mention some elements capable of existing in allotropic modifi- 

 cations. 



87. What relation exists between the properties of elements and the 

 properties of the compounds formed by their union? 



