218 MINERAL WATERS, WELL-WATERS, ETC. 



to dissolve this acid again in part or wholly. This 

 difficulty may be avoided by making a very simple 

 modification. A flask of the capacity from 400 to 

 500 cubic centimetres is used arranged as before. 



Fig. 



The apparatus being completely free from air, a 

 caoutchouc tube is placed upon the end of the delivery 

 tube to pass to the top of the small graduated bell- 

 glass and kept there at a certain height. 



The height is regulated on the supposed volume of 

 gas that boiling furnishes. It is at first gradually 

 heated so as to cause a small quantity of water to pass 

 out from the flask, the volume of which is accurately 

 measured and subtracted from the first volume taken ; 

 the delivery tube is then placed under the bell-jar, after 

 which the temperature is gradually increased till the 

 boiling point is reached. The bell-jar being nearly 



