HOUSEHOLD CHEMISTRY 99 



represented in the equation CaCOs + H 2 CO3 >H 2 Ca 



in which the resulting new substance known as acid calcium 



carbonate is soluble in water. 



Whether these chemical changes occur as a series of steps 

 in the order indicated, or are more or less coincident, is of 

 far less importance than it is to have set forth in the equa- 

 tions that which is known to be true concerning what sub- 

 stances as factors enter into the chemical change, and what 

 substances result as products. 



3. Learn definitions for acid, base, and salt as used in 

 Chemistry. Show very definitely how the substances whose 

 formulae are CaCOa, CaO 2 H 2 , and H 2 CO3, respectively, meet 

 these conditions. It will be noted that in the formula for 

 the acid calcium carbonate there appears not only the 

 metallic atom Ca from the base, and the radical CO 8 from the 

 acid, but some H from the acid appears also in the formula 

 of the salt. This formula H 2 Ca(CO3) 2 is a good illustra- 



tion of the class of so-called acid salts. It must be remem- 







bered, however, that it is upon the presence of the hydrogen 

 atoms in the molecule of the acid salt, and not upon the 

 effect shown by litmus paper, that the classification of salts 

 as normal and acid depends. In the case of the salt known 

 as acid sodium carbonate (HNaCOs) the solution as shown 

 by use of litmus paper is strongly alkaline. 



4. Note the appearance and taste of both sodium car- 

 bonate (Na 2 C03) and acid sodium carbonate. The latter is 

 "baking soda," and the former is known as "sal-soda," 

 and as "washing soda." Test the gas given off as a little 

 hydrochloric acid is added to portions of each of these 

 salts in test tubes. (Hold dowh in the tube above the 



