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

POTASSIUM CHLORATE. 117

of neutral sodium chromate. Before titrating with sodium thio-
sulphate, acidify strongly and dilute well, in order that the color

of the chromate may not interfere with the end-point. From the

total volume of thiosulphate used deduct the amount which

corresponds to the iodine set free by the chromate. The current
yield is now much better, on account of the addition of the chro-

mate, and remains above 30% for a longer time; the total yield of

"active" chlorine, computed as above, now amounts to from

14 to 16 g. per liter.

C. If experiment A is repeated without cooling the solution,

the current yield falls very rapidly to below 30%, and the quantity

of active chlorine produced before this point is reached amounts

to only about 5 or 6 g. per liter.

Test qualitatively the bleaching action of the hypochlorite
solutions obtained by adding a little to some indigo solution.

Potassium Chlorate. As electrolyte use a solution containing

100 g. of potassium chloride and 1 g. of potassium pyrochromate

in 250 c.c. of water. Use a 600 c.c. beaker for the electrolyzing

vessel, and cover it with the two halves of a divided watch glass.

The electrodes should be, as before, of sheet platinum. Maintain
at the anode a current density of 20 amperes per 100 sq. cm. and

at the cathode a higher density. Keep the temperature at 40-60°,

using a small flame if necessary to add to the heating effect of the

current. A source of current at from 6 to 10 volts will suffice to
maintain the necessary potential. Pass a slow stream of carbon

dioxide continuously into the solution between the electrodes. To

obtain a good yield, about 60 ampere-hours are required; thus for

an anode surface (one side) of 25 sq. cm. the experiment must be
continued 14 hours. If necessary it is permissible to interrupt the

electrolysis. Occasionally replace the water lost by evaporation.

A little potassium chlorate crystallizes out during the electroly-

sis, but the main part is obtained after cooling; drain the crystals
with suction and wash with a little cold water. To determine the

entire yield of chlorate, dilute the mother-liquor to 500 c.c. and

titrate a part of it with ferrous sulphate: boil 10 c.c. of the solution

in a flask in order to drive out the free chlorine, replace the air by
means of carbon dioxide, and after cooling add 50-70 c.c. of a

0.1-normal ferrous ammonium sulphate solution acidified with

sulphuric acid. Close the flask with a Bunsen valve and boil the

solution ten minutes. After cooling, dilute the liquid to twice its