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

18 THE ELEMENTS.

nesium powder and in the latter stick a strip of filter paper (10 X

2 cm.) which has been moistened with concentrated potassium

nitrate solution and dried. Set fire to the paper by touching it

with a torch made by fastening a wad of asbestos to the end of an

iron wire, wetting the asbestos with alcohol and setting fire to the

alcohol. The torch ignites the paper which has been impregnated

with potassium nitrate, the burning paper sets fire to the mag-

nesium and the burning magnesium ignites the thermite mixture.

As soon as the reaction has started add the remainder of the

charge from an iron spoon, not too much at one time, but still

rapidly enough so that the mass in the crucible is kept in a state

of brilliant incandescence until the reaction is ended. It is

advisable for the operator to wear blue glasses and a heavy glove

and the experiment should be performed in a place where no

danger can result from flying sparks.

After cooling, break the crucible and hammer away the slag

of fused aluminium oxide from the regulus of metallic manganese.

The slag is very hard and will scratch glass. Yield of man-

ganese, about 120 g. Dependent preparation, Potassium Per-

manganate, Electrolytically No. 84.

3. Chromium from Chromic Oxide.
   Chromium cannot be prepared, at least not on a small scale, according to
   the directions given for manganese, because the heat liberated in the reaction
   between chromic oxide and aluminium is not sufficient of itself to melt the
   aluminium oxide. It is, therefore, in this case necessary to heat the crucible
   and its contents before starting the reaction, or to add to the mixture a little
   chromate which, by reacting more violently with the aluminium, affords the
   necessary heat.


4. Mix about 70 g. of chromic oxide (No. 30) with one or two
   grams less than the calculated amount of aluminium powder; place
   the mixture in a clay crucible, which should be about two-thirds
   filled. Add to the above mixture 10 to 15 g. of ignition powder,
   1

and place the crucible in a glowing charcoal furnace whereby the

ignition powder ignites, and the mass enters into violent reaction.

Finally remove the crucible from the furnace, allow it to cool and

break it, together with the slag, away from the metallic chromium.

(^1) One part aluminium powder mixed with 10 parts of barium peroxide.
Such ignition powder can be purchased all prepared for thermite reactions.