226 HEAVY METALS OF GROUPS I AND IIApparatus: 8-inch porcelain dish.
2-liter common bottle,
suction filter and trap bottle,
iron ring and ring stand.
Bunsen burner.Procedure: Dissolve the blue vitriol and the Rochelle salt each
in 200 cc. of hot water, filter the solutions separately if they are
not clear, and when they are nearly cold mix them together in the
8-inch dish. In the meantime dissolve the sodium hydroxide in
200 cc. of water, cool it completely, filter if not clear, and pour
it in a thin stream into the mixture in the dish, stirring constantly
and being careful not to allow the mixture to get more than barely
warm from the reaction. A clear deep blue solution results.
Dissolve the 10 grams of dextrose in 100 cc. of water. Heat the
cupric salt solution to boiling; add the dextrose solution 10 cc.
at a time until the blue color of the cupric salt is discharged. To
determine this point it is necessary after stirring to wait a few
moments to let the red precipitate of CU2O settle so that one can
observe the color of the upper layer of solution. Avoid adding
more than necessary of the dextrose since this substance is turned
brown by the hot alkali and the brilliant red color of the cuprous
oxide is dulled. Pour the contents of the dish into about 1 liter
of cold water in a 2-liter bottle and mix thoroughly; let settle for
about 15 minutes. Although the supernatant liquid still appears
turbid at this point, the amount of suspended cuprous oxide is
very small. Decant this turbid liquid very carefully so as not to
stir up the cuprous oxide. As the bottle is gradually tipped, the
heavy cuprous oxide finally settles into the shoulder of the bottle
and all but about 100 cc. of the liquid runs over the lip. Fill the
bottle again with water, mix, let settle, and decant as before.
Transfer the cuprous oxide to the suction filter, and as soon as the
last drop of water is sucked into the compacted cake in the bottom,
stop the suction. Then wash with 2 successive portions of 15 cc.
each of water and 3 successive portions of 15 cc. each of alcohol,
following the directions of the preceding preparation. Place the
cuprous oxide on a watch glass on the hot plate, and as soon as
the alcohol is evaporated, put up the product in a 2-ounce cork-
stoppered bottle.