HYDROCHLORIC ACID. 



211 



A tea-spoonfull of common salt is introduced into a 

 test-tube, with about the same 

 bulk of water. Half as much 

 acid is added, then the mixture 

 gently heated, and the acid gas 

 led into water, as shown in the 

 figure. Water absorbs, at ordi- 

 nary temperatures, 480 times 

 its own volume, of the gas. 

 There is no occasion, for the 



purpose of experiment, to carry on the process till it is 

 thus saturated. A few minutes will suffice to make an 

 acid strong enough to dissolve zinc. 

 Explain the 52 1. EXPLANATION. Hydrated sulphu- 

 process. r j c %(,[& fr as always a strong tendency to 



form metallic salts. In this case it takes the metal, 

 sodium, from the common salt, and thereby converts 

 itself into sulphate of soda. At the same time it gives 

 back hydrogen to the salt, in place of its lost sodium, 

 converting it, by the exchange, into hydrochloric acid. 

 The process just described, is the one always employed 

 in the manufacture of hydrochloric acid. 



522. ACTION OF HYDROCHLORIC ACID ON 



What metals ,, , . , -IT i 



does hydro- METALS. Hydrochloric acid dissolves tm> 

 chloric dis- an( j a ]j o f fa e meta | s w hich precede it in 



solve ? 



the chapter upon metals. For tin, a hot 

 and concentrated acid must be employed. 



523. The solution depends on the fact 



On what does 



the solution that the metals take chlorine, from the 

 depend? hydrochloric acid, thereby converting 



themselves into soluble chlorides. The hydrogen then 



