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

44 CHANGES OF CONDITION.

colored pseudo-solution, that appears perfectly clear by trans-

mitted light. First remove the excess of hydrogen sulphide by a

stream of hydrogen, then place the solution in a dialyzing tube of

parchment paper, and suspend the latter in a vessel of distilled

water. If the tube is free from imperfections, almost none of the

yellow material passes into the outer solution, while the salts

present are gradually removed by diffusion. Replace the outside

water with fresh water, at first every six hours, later every twelve

hours, and continue the dialysis about four days.

Dilute a part of the antimony sulphide solution to ten times its

original volume, and carry out the following experiments:

1. Place roughly equivalent, normal solutions of potassium
   chloride, barium chloride, and aluminium chloride in three burettes
   and add each, drop by drop, to three separate portions of 20 c.c.
   each of the colloidal antimony sulphide until the complete precipi-
   tation of the latter is accomplished. It may be necessary to repeat
   the experiment before the right end-point is obtained, noticing
   carefully when the precipitant causes the supernatant solution to
   change from yellow to colorless. It will be found that the largest
   amount of precipitant is required in the case of potassium chloride,
   the smallest in the case of aluminium chloride. The precipitating
   power of equivalent amounts of salts for colloids of this class
   increases with the valence of the cation.


2. Shake several portions of 10 c.c. each of the antimony sul-
   phide for 1 minute with 2.0, 1.0, 0.5, 0.2, and 0.1 g. respectively of
   powdered barium sulphate. The pseudo-dissolved material is

adsorbed by the solid. Determine what quantity of the barium

sulphate is just sufficient for complete adsorption.

Test also, for comparison, the precipitating power of wood

charcoal and animal charcoal.

22. Adsorption of Iodine by Charcoal. Adsorption Curve.
    For a more accurate study of adsorption phenomena, charcoal

is particularly well suited, since under ordinary conditions it is

an indifferent substance, and has a constant surface. Place in

each of four 200 c.c. glass-stoppered bottles 2 g. of washed, dried,

and ignited animal charcoal and 50, 75, 90, and 95 c.c. of alcohol;

then add 50, 25, 10, and 5 c.c. respectively of a normal alcoholic

iodine solution, so that the volume in each bottle will be 100 c.c.