18 NOTES ON LABORATORY MANIPULATIONof the hot charcoal is oxidized to carbon monoxide, which then
reduces some of the strontium sulphate, it being itself changed
to carbon dioxide thereby; the latter gas comes in contact with
incandescent charcoal, and carbon monoxide is again produced.
Reactions in the dry way are usually carried out in crucibles
of iron, clay, or graphite, according to which one is least attacked
by the reagents. For rather moderate temperatures the crucible
may be heated over a flame; otherwise the requisite temperature
can be obtained in a furnace.
(l\ The form of furnace to be rec-
^" ~1~^ ommended for this work is repre-
d IUu-^ Z> sented in Fig. 6. It consists of a
cylinder of fire clay, 7 inches high
and 7| inches in external diameter,
which is surrounded by a sheet-
iron casing. It is heated, as
shown, by a blast lamp intro-
duced through an opening in the
PIG g lower part of one side. If a suit-
able air blast is not available, a
gasoline blow torch (such as is commonly used by plumbers) is
serviceable.
When such a furnace as that described is heated as hot as possible
with a well-regulated mixture of gas and air, a temperature of
about l,450°C. can be obtained. For carrying out ordinary chem-
ical preparation work an accurate enough measure of the tem-
perature is given by the color of the glowing interior of the furnace,
and the approximate centigrade values corresponding to different
colors are as follows:
Incipient red heat... 550°
Dull red heat. 650°
Red heat. .... 800°
Bright red heat 1,000°
Yellow heat. 1,200°
White heat.. 1,350°
13 GAS GENERATORS
(a) Carbon Dioxide, Hydrogen, and Hydrogen Sulphide. The
simplest form of generator for these gases in shown in Fig. 7.
The solid material, cracked marble for carbon dioxide, feathered