146 



The Phosphates of America. 



is closed and the apparatus is allowed to stand in a warm place 

 (say at 80 C.) for two hours .with occasional agitation. The 

 carbonic-acid gas passes off through C, the sulphuric acid, however, 

 preventing the escape of any moisture that might otherwise ac- 

 company it. At the end of two hours B is opened, and the air 



SCHROTTER'S APPARATUS FOR THE ESTIMATION OF CARBONIC-ACID GAS. 



is drawn through the apparatus by suction applied to a piece of 

 thin India-rubber tubing connected with D in order to sweep out 

 all traces of the CO 2 . B is then closed and the apparatus is 

 allowed to become quite cold, when it is brought back to the scale 

 and weighed. The difference between the present and the first 

 weight -*- 2 represents the CO 2 in one gramme of the normal 

 sample. 



