144 



JUNIOR GRADE SCIENCE 



68. HYDROCHLORIC ACID, 



i. Preparation of hydrochloric acid gas. Fit up the apparatus shown in 

 Fig. 98. Remove the india-rubber stopper of the flask and place in it a 

 small quantity of rock salt in small pieces, or some thoroughly dried common 

 salt. Pour some strong sulphuric acid into the wash-bottle shown in the 

 middle of the illustration. Re-insert the india-rubber stopper into the 

 flask and pour down the acid funnel enough of a mixture J of strong sulphuric 



Fio. 98. Preparation and collection of hydrochloric acid gas. 



acid and water to cover the salt in the flask. Gently warm the flask. Collect 

 jars of the gas which is evolved (after it has bubbled through the strong 

 sulphuric acid in the wash- bottle and so become freed from water vapour) 

 in gas jars by downward displacement in the way the illustration makes 

 clear. When each gas cylinder is full, which you can tell by holding a blue 

 litmus paper just below the top of the outside of the cylinder until it is 

 turned red, cover it with a ground-glass plate, with the ground side under- 

 neath. As the cylinders are filled set them on one side for examination 

 as presently described. Collect four jars of gas in this way. 



ii. Properties of hydrochloric acid gas. (a) Raise the glass plate from 

 the first jar and plunge a lighted taper into the gas. The flame is extinguished 

 and the gas does not burn. Quickly replace the glass plate. 



(6) Into the same jar drop a piece of moistened blue litmus paper and 

 replace the glass plate. The paper is turned red, showing the gas has acid 

 properties. 



(c) Observe the fumes which the gas forms with the air when the glass 

 plate is removed from a cylinder full of the gas. This is due to the very 

 strong power of absorbing moisture possessed by hydrochloric acid gas. 



1 One part of acid and one of water are convenient proportions. Be careful gradually 

 to pour the acid into the water and not the water into the acid when mixing them, 

 keeping the mixture well stirred throughout the process. 



