HEATING.
in organic ultimate analysis, is suitable. Very high temperatures
may be obtained with the blast lamp if the part of the tube to
be heated is surrounded by an asbestos chamber like that shownin Fig. 4. The bottom of the chamber should measure about
10 X 16 cm. and the height about 13 cm. In the bottom is a
large hole for the flame of the blast lamp to enter; in the two
end walls are holes through which the tube to be heated just
fits. As a cover, a piece of asbestos board serves, which is
loosely laid on top of the box and is provided near the four
corners with round holes of 2 cm. diameter. The box is held
together by means of wire fastenings. For heating long tubes
Fig. 4. ;. 6.to very high temperatures, a Mitscherlich tube furnace can be
used which is 50 cm. long and is made of sheet iron lined with
fire-clay.
For providing and maintaining constant temperatures, up to
1500°, the platinum electrical resistance furnace, and for tem-
peratures above 2000° the carbon resistance furnace, are invalu-
able. Although such furnaces would be very convenient for
some of the preparations described in the following pages, they
may be dispensed with on account of their high price.
Many different forms of apparatus have been devised for
uniformly heating flasks and similar vessels to moderate temper-
atures. Besides sand baths, Babo's boiling funnel (Fig. 5),
which is capable of wide application, and nickel air baths, are
particularly to be recommended.
When liquids are to be boiled for a considerable length of
time, the flask should be provided with a condenser or a wide
glass tube held either vertically or inclined so that vapors will
condense and the liquid run back into the flask. This is known
as heating with a reflux condenser.