388 



Journal of the Asiatic Society of Bengal. [August, 1910. 



c 





bichromate solution. The difference between the combined 

 ferrous iron and free iron gives the quantity of ferrous iron 

 already present. The ferric iron is then easily estimated by 

 precipitating the total iron with ammonia and subtracting the 

 ferrous and free iron from the total iron thus found. 



In order to test how far the hydrogen method of estimat- 

 ing iron is successful quantitatively we carried on some blank 

 experiments using the apparatus sketched below. The carbon 

 dioxide was obtained by heating sodium bicarbonate in the 

 hard glass tube A. The Erlenmeyer flask contains the weighed 

 quantity of pure iron wire and the tap-funnel contains the 

 dilute acid (1 : 4). 



J= 



A 



C 



The hydrogen was collected in a 250 c.c. volumetric 

 measuring flask with a long neck over strong caustic potash 

 contained in a basin. In order to test whether all the air has 



bon dioxide, a long tube with a st 

 used and the caustic notash was 



with 



When 



no more bubbles collected in the tube, the measuring flask 

 filled with caustic potash solution was substituted for the tube. 

 The acid was then dropped in and the hydrogen evolved is 

 driven out by the carbon dioxide and collected in the flask so 

 long as any bubbles come out. The flask was next transferred 

 to a deep pneumatic trough and the volume of water ascer- 



