LAWS OF CHEMICAL COMBINATION. NOTATION. 39 



H + ci = H Cl or H + C1 = HC1 (hydrochloric acid). 



- 1 + I O I = HlO or H,+O = H 2 O (water). 



I H I ' ' l ' 



2LI _ 



H | + | N | = I N'H 3 | or H 3 +N = NH 3 (ammonia). 



1"! 



= C HJ or H<+C = CH 4 (marsh gas). 



35. Significance of Equations. Every chemical equation 

 expresses a great deal in an exceedingly condensed manner. 

 It shows : 



1st. What and how many elements are concerned in the reaction. 



2d. How these elements are combined before and after the chemical 

 change has taken place. 



3d. The proportion by weight of every constituent in the compounds. 



Iii the case of gases a fourth point is shown, to which we 

 have just alluded, viz., the proportion by volume. 



We will give you one more example to study; try to 

 determine the application of the three points above named. 

 The names of the bodies are not familiar, but that need not 

 be a source of confusion : 



Calcium Hydrochloric Calcinm Carbonic 



Carbonate. Acid. Chloride. Water. Anhydride. 



CaCO 3 + 2HC1 = CaCl 2 + H 2 O + CO 2 

 40 + 12 + (1GX3) 2(1+35.5) 40+(35.5X2) (1X2) + 16 12+(16x2) 



100 73 "Til 18 44 



~17Z~ ~173 



