56, 57] Estimation of Carbon Dioxide 37 



tip reaches nearly to the bottom of the flask a. Above, the 

 pipette is joined to the tube c by about 6 inches of india- 

 rubber tubing which is closed by a clip. 



56. The Determination. — Weigh about a gram of the 

 pure Iceland spar, and transfer it to the flask a. Next weigh 

 the tube f, and replace it in its position. Fill the tube b with 

 dilute hydrochloric acid, and close the clip so that no acid 

 may drop from the tip of the pipette. Replace the stopper in 

 the flask, and the whole apparatus will appear exactly as in the 

 figure, excepting that the aspirator will not be in position. 

 Loosen the clip above b, so that the acid may flow down slowly 

 upon the spar. When all effervescence has ceased, close the 

 clip and bring the acid to a boil by placing a Bunsen beneath 

 it j next, lower the flame, attach g to the aspirator or to a 

 pump (fig. 15), loosen the clip, and allow air to pass through 

 the apparatus for fifteen minutes. The speed of the air current 

 should be so regulated that the bubbles may be counted as 

 they pass through the sulphuric acid bulb. When the air 

 has been passing for the prescribed time, stop the aspirator, 

 turn off the stopcocks in /, and remove the tube : weigh it. 

 The amount which it has gained will represent the amount of 

 C0 2 which has been given off from the spar. 



Section IL— VOLUMETRIC ESTIMATIONS 



57. In volumetric analysis the balance is to a great extent 

 replaced by instruments which measure volumes. 



The principle of volumetric analysis is best explained by 

 taking an example. Suppose that we had a solution of sul- 

 phuric acid of which we knew the exact strength, every c.c. 

 containing a certain weight of pure H 2 S0 4 . It is required by 

 means of this solution to find out how much pure KHO exists 



