METHODS FOR QUANTITATIVE DETERMINATIONS. 263 



into ferrous compounds before titration. This conversion is accomplished by 

 heating the solution of a weighed quantity of the ferric compound with nascent 

 hydrogen i. e., with metallic zinc and dilute sulphuric acid in a flask 

 arranged as the one spoken of above, and shown in Fig. 37. 



FIG. 37. 



Flask for dissolving iron for volumetric determination. 



A very much quicker reduction of the ferric into a ferrous compound may be 

 accomplished by adding very slowly with constant stirring a saturated solution 

 of sodium sulphite to the boiling, acidified iron solution contained in the flask 

 until the liquid becomes colorless. All excess of sulphur dioxide is expelled 

 before titrating, by boiling the solution (which should contain a sufficient 

 quantity of hydrochloric acid to decompose all sodium sulphite) for about ten 

 minutes in a flask, arranged as the one mentioned above. 



One c.c. of deci-normal potassium permanganate, containing of this 

 salt 0.0031534 gramme, is the equivalent of: 



Gramme. 



Amyl nitrite, CgH^NO.j 0.003153 



Barium dioxide, BaO 2 0.058390 



Calcium hypo-phosphite, Ca(PH 2 O 2 ) 2 0.002121 



Ethyl nitrite, C 2 H 5 NO 2 0.037435 



Ferric hypophosphite, Fe 2 (PH 2 O 2 ) 6 0.002088 



Ferrous ammonium sulphate, Fe(NH 4 ) 2 (SO^ 2 .6H 2 O . . . 0.039130 



Ferrous carbonate, FeCO 3 0.011573 



Ferrous oxide, FeO 0.007195 



Ferrous sulphate, FeSO 4 0.015170 



Ferrous sulphate, crystallized, FeSO 4 .7H 2 O 027742 



Hydrogen dioxide, H 2 O 2 (see explanation, page 84) . . . 0.001696 



Hypophosphorous acid, HPH 2 O 2 0.001647 



Iron, in ferrous compounds, Fe 005588 



Oxalic acid, crystallized, H 2 C 2 O 4 .2H 2 O . . . . . 0.006285 



Oxygen, O 0.000798 



Potassium hypophosphite, KPH 2 O 2 0.002598 



Potassium nitrite, KNO 2 . . . . . . . . 0.042480 



Sodium hypophosphite, NaPH 2 O 2 .H 2 O 0.002646 



Sodium nitrite, NaNO 2 0.034465 



