GENERAL REMARKS REGARDING ELEMENTS. 69 



Whenever the exchange of atoms takes place between univalent 

 and trivalent elements, three of the first are required for one of the 

 second, as in the case of the action of sodium hydroxide on bismuth 

 chloride : 



Na OH /Cl /OH Na Cl 



Na OH + Bi Cl = Bi OH + Na Cl 

 Na OH \C1 \OH Na Cl 



or 



3NaOH + BiCl 3 = Bi(OH) 3 + SNaCl. 



In the following examples of double composition an exchange 

 takes place between the atoms of metallic elements, or between the 

 metallic elements and the hydrogen. The student, in completing the 

 equations, has also to select the correct quantity, i. e. y the correct 

 number of molecules of the factors required for the change. The 

 interrogation marks indicate that more than one atom or one molecule 

 of the substance is needed for the reaction. 



Na' + H'Cl Cu"SO 4 + H/S 



H/SO 4 + K'(?) Ba"Cl 2 + Na/SO 4 



Ca" + H'Cl (?) = Na/CO 3 + H 2 'SO 4 



Fe" + H/SO 4 == Bi"'(NO 3 ) 3 + K'OH (?) = 



H'Cl + Ag'N0 8 = AV"(S0 4 ) 8 + K'OH (?) = 



Ca"Cl 2 + Ag'N0 3 (?)= A1/^(S0 4 ) 3 + C 



Bi'"Cl 3 + Ag^N0 3 (?) = Fe/"Cl 6 + A 



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 the 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 toward other elements or compounds; acid, 

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

 nized 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 interest, 

 should be noticed also. 



All students having the facility for working in a chemical labora- 

 tory are strongly advised to make all those experiments and reactions 



