IN CIIEMISTRY. 10 1 



4. Represent the reaction, tn\'ifrdkfag CO $,'?. bowing the 



atomic weights, as in the >rpqrajion of^Q on page 28. 



In this experiment the acid' exchanges its Tiydrogen for 

 the calcium, producing calcium chloride (CaCl 2 ) on the 

 one hand, and carbonic acid (H 2 CO 3 ) on the other. 

 But the carbonic acid is so unstable that it immediately 

 becomes decomposed into water, which remains behind, 

 and into carbonic anhydride, which comes off as a gas 

 with brisk effervescence. The decomposition may be 

 represented as follows : 



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



(Calcium Car- ) , j (Hydrochlo- ) _ j (Calcium I / Wa ^ r \ , j (Carbonic 

 bonate) ] + \ ric Acid) \~\ Chloride) f + + 1 Anhydride) 



Ca C O 3 2(H CD Ca Cl a + H 2 O + C O 3 



40 + 12 + 3x16 2(1+35.5) 40 + 2(35.5) 2 + 16 12 + 2x16 



The CO liberated = T y s of the materials used ; the H a O = r V 8 s, and the 

 CaCl 3 = HI- 



5. Should one take a light into a room where the gas is 

 escaping ? 



Great care should be used, since coal-gas is combus- 

 tible, and when mixed with O in the proper proportion 

 explodes with great violence. Severe accidents frequently 

 occur from a neglect of this precaution. 



6. What causes the difference between a No. i and a No. 4 

 pencil? 



(See Chemistry, page 67.) 



7. Why does it dull a knife to sharpen a pencil 1 ! 



(See Chemistry, page 67.) 



