METHODS FOR QUANTITATIVE DETERMINATIONS. 417 



Acetic acid, HC 2 H 3 O 2 ........ 0.05958 



Boric acid, H 3 IK), .......... 0.06154 



Citric acid, crystallized, H.,C 6 H 5 O 7 .H 2 O ...... 0.06950 



Hydrobromic acid, HBr ......... 0.08036 



Hydrochloric acid, HC1 ......... 0.03618 



Hydriodic acid, HI .......... 0.12690 



Hypophosphorous acid, HPH 2 O 2 . ...... 0.06553 



Lactic acid. HC 3 H 5 O 3 ......... 0.08937 



Nitric acid,' HNO 3 .......... 0.06257 



Oxalic acid, crystallized, H 2 C 2 O 4 .2H 2 O ...... 0.06255 



Phosphoric acid, H 3 PO 4 (to form K 2 HPO 4 ; with phenol-phthalein) 0.04864 

 Phosphoric acid, H 3 PO 4 (to form KH 2 PO 4 ; with methyl-orange) . 0.09729 

 Potassium dichromate, K 2 Cr 2 O 7 (with phenol-phthalein) . . 0.14614 

 Sulphuric acid, H 2 SO 4 ......... 0.04867 



Tartaric acid, H 2 C 4 H 4 O 6 . . ..... . . . 0.07446 



Oxidimetry. A normal oxidizing solution is one which will 

 liberate from a liter as much oxygen as is chemically equivalent to 

 one gram-atom of hydrogen. This is one-half gram-atom, or 8 

 grammes of oxygen, for 



H 2 + O = H 2 0, or H + = 



The substances generally used in oxidimetry are potassium per- 

 manganate and potassium dichromate. 



Potassium permanganate, KMnO 4 , 156.98, is chiefly used for 

 normal or decinormal oxidizing solution, and the titration is always 

 carried out in solution acidified with sulphuric acid. When the salt 

 breaks up to give off oxygen, it does so in this manner : 



2KMn0 4 + 3H 2 SO 4 = K 2 SO 4 + 2MnSO 4 + 5O + 3H 2 O. 



The oxygen is used in oxidizing the substance which is titrated. 

 The object of adding the acid is to facilitate the decomposition of 

 the KMnO 4 and to take up the potassium and manganese to form 

 salts, which being colorless form a colorless solution. 



As 2 molecules of permanganate give up 5 atoms of oxygen, the 



quantity to be taken to liberate \ atom or 8 gm. is - ^~* = -f^> 



or l O i. e., J the molecular weight in grammes, or 31.396 gm. It 

 is this quantity which is contained in one liter of normal solution. 



When oxalic acid is oxidized with permanganate solution this reaction 

 takes place: 



H 2 C 2 4 .2H 2 + O = 2C0 2 + 3H 2 O, 



or more fully, 



5H 8 C 2 4 .2H 2 + 2KMn0 4 + 3H,SO 4 = 10CO 2 + 1^H 2 O + K 2 SO 4 -f 2MnSO 4 . 



