420 ANALYTICAL CHEMISTRY. 



All nitrites react thus : 



MNO 2 + O = MNO 3 , where M = metal. 

 MNO 2 = 1 atom O = quantity liberated by 2 liters KMnO 4 , 



MNQ 2 = i = l liter *. KMn0 4 , 

 2 1 



MNO, = 1 liter ^ " 



2 X 10 10 



MNO, 



= ! c c . 



2 X 10 X 1000 10 



In this manner all other equivalents are found. The reactions 

 between permanganate and ferrous salts, and hydrogen dioxide respect- 

 ively, are expressed in these equations : 



2FeS0 4 -f H 2 S0 4 + O = Fe 2 (SO 4 ) 3 + H 2 O. 

 H 2 2 + O = H 2 + 20. 



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

 salt 0.0031396 gramme, is the equivalent of: 



Gramme. 



Ferrous ammonium sulphate, Fe(NH 4 ) 2 (SO 4 ) 2 6H.,O . . . 0.038934 



Ferrous carbonate, FeCO 3 0.011505 



Ferrous oxide, FeO 0.007138 



Ferrous sulphate, FeSO 4 ........ 0.015085 



Ferrous sulphate, crystallized, FeSO 4 .7H 2 O 0.027601 



Ferrous sulphate, dried, 2FeSO 4 + 3H 2 O 0.017767 



Hydrogen dioxide, H 2 O 2 0.001688 



Iron, in ferrous compounds, Fe - 0.005550 



Oxalic acid, crystallized, H 2 C 2 O 4 .2H 2 O 0.006255 



Oxygen, O 0.000794 



Potassium nitrite, KNO 2 . . . . . . . . 0.004227 



Sodium nitrite, NaNO 2 0.003428 



Potassium dichromate, K 2 Cr 2 O 7 = 292.28. Whenever this salt 

 oxidizes other substances in acid solution it breaks up according to 

 this equation : 



K a CrA + 4H 2 S0 4 = K 2 SO 4 + Cr 2 (SO 4 ) 3 -f 3O + 4H 2 O. 



That is, one molecule of K 2 Cr 2 O 7 gives up three atoms of oxygen. 

 Hence to make a normal solution one-sixth the molecular weight of 

 K 2 Cr 2 O 7 (48.7133 grammes) is taken in the liter, and one-tenth this 

 quantity, equal to 4.8713 grammes of the pure salt, for deci-normal 

 solution. 



The disadvantage of this solution is that the final point of titration cannot 

 be well seen, for which reason in the determination of iron, for which it is 



