Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

126 OXY-ACIDS OF SULPHUR.

it is necessary to supplement the heating effect of the current.

The formation of permanganate begins as soon as the current starts;

red films of solution form at the anode surface and sink to the

bottom of the beaker. At the end of 30 minutes, and then after

every 20 minutes, stir the bath well and take samples of 5 or

10 c.c. with a pipette for the purpose of determining the current

yield.

1

Acidify the sample with sulphuric acid, whereupon the

precipitate, which is mainly ferric hydroxide, dissolves; decolorize

the hot solution with a measured excess of 0.1-normal oxalic acid

and titrate back at 60° with 0.1-normal permanganate. The per-

manganate solution obtained in this manner is so dilute that it

does not pay to attempt to crystallize the solid salt. The current

yield in several experiments made in the author's laboratory with

1.5-3.0 amperes was as high as 25% at the end of 45 minutes; in

the next hour it sank to about 10%.

85. Barium Ferrate, Ba[FeO 4 ].
    Clamp a 50-75 c.c. flask in an upright position and place in it a
    mixture of 10 g. of fine iron filings and 20 g. of potassium nitrate.
    Heat with a flame until a reaction takes place and the iron burns
    with a shower of sparks. After cooling break the flask, extract
    four times with 50 c.c. of ice water, and filter the combined extract
    through asbestos. Pass the deep violet-red filtrate again through
    a fresh asbestos felt and precipitate it immediately with a solution
    of barium chloride. After an hour drain the precipitate of barium
    ferrate on a hardened filter, wash it with alcohol, then with ether,
    and dry at the room temperature in a vacuum desicccator. Yield,
    1.0 to 1.5 g.

(e) Oxy-acids of Sulphur and Their Salts.

For sulphurous acid the two following constitutional formulas^2 have been

proposed:

O<. •OH .OH

0 XH °-<0H

Unsymmetrical Formula. Symmetrical Formula.

(^1) Compare the directions in Preparations 14 and 74.
2
Constitutional formulas of the complex inorganic acids apply only with
a certain reservation: They characterize the ability to react only in one par-
ticular direction, and show, of several possibilities, only one definite con-
dition of the acid (see cyanic and hypochlorous acids). They are of value,
however, as aids to the memory.