34 Estimations occurring in Agricultural Analysis [55 



and the C0 2 evolved, after bubbling through the H 2 S0 4 in c, 

 is allowed to escape into the air. The apparatus is warmed 

 and the air expelled as before, the stopper and tap on b of 

 course being opened. The apparatus is then weighed, and 

 the percentage of C0 2 calculated as before. 



55. Method p. By direct weighing.— Several forms 

 of apparatus are used for this estimation, perhaps the simplest 



Fig. 22. 



being that recommended in Crookes's 

 Chemical Analysis.' 1 



Select Methods of 



1 For the benefit of those who wish to try this method, I quote the 

 following : 



H. T. S. Gladding uses an apparatus for the estimation of carbonic 

 acid by absorption. It consists of the ordinary generating flask, followed 

 by an empty U tube to retain condensed water vapour ; this is succeeded 

 by four potash bulbs of the Geissler form. The first of these contains 

 concentrated sulphuric acid to dry the gas. The next two contain potash 

 solution of Sp. G. 1 '27 for absorbing the carbonic acid ; the last contains 

 concentrated sulphuric acid to absorb the moisture given up by the potash 



