CALCIUM MOLYBDATE 333Apparatus: clay crucible of 600-cc. capacity,
gas furnace.
6-inch iron sand bath,
pail of sand,
hammer.
Procedure: Heat the chromic oxide in the crucible in the gas
furnace for 40 minutes or longer. Melt the potassium dichromate
in a clean iron pan, and pulverize it in a mortar after it has solidi-
fied. Mix the chromic oxide, potassium dichromate, and granu-
lated aluminum thoroughly in a mortar. Make a fuse powder with
2 grams of granulated aluminum and 20 grams of barium peroxide.
Take half of the fuse powder and mix it with twice its bulk of
the main charge. Hold a rather wide test tube in the middle of
the crucible, pack the charge around it, and withdraw it carefully,
leaving a deep hole in the middle. Carefully pour the mixture
of fuse powder and charge into the bottom of the hole; pour the
fuse powder on top of it in the hole; and insert a strip of mag-
nesium ribbon into the fuse powder. Imbed the crucible in a pail
of dry sand and place the pail under the hood in the furnace room
at a distance from any woodwork. Start the reaction by igniting
the end of the magnesium ribbon with a gas flame. It is advisable
not to look directly at the reaction because of the intense light,
and to keep at a little distance to be out of the way of flying sparks.
When the crucible has cooled, break it with a hammer and sepa-
rate the regulus of metallic chromium from the slag of fused
aluminum oxide.QUESTIONS- What is approximately the position of chromium in the
electromotive series? What bearing does this have upon the
question of reducing chromic oxide? - What metals can be used in place of aluminum in the alumino-
thermic process? - What other metals than chromium can be advantageously
prepared by this process, and why?
PREPARATION 67
CALCIUM MOLYBDATE, CaMoO 4
Molybdenum trioxide, MoO 3 , is, like sulphur trioxide, an acid
oxide. It is a white, solid substance, sparingly soluble, but