68 WATER AND SOLUTION
(b) To try the effect of dry steam on hot magnesium,
clamp a piece of Pyrex glass tubing 1 cm. in diameter and
18 inches long in position at an angle of about 5° with the
horizontal. Connect the lower end of the tube with a flask
in such a manner that steam generated from the water in the
flask may be conducted through the tube. Connect the
upper end of the tube with a delivery tube, arranged so that the
gases produced in the reaction may be collected over water
in a trough. Place some pieces of magnesium ribbon in the
middle of the tube. Pass steam through the tube and heat it
cautiously at the lower end until the condensed water is
evaporated and the steam is "dry." Get the whole length
of the tube well warmed with the burner, so that it appears
perfectly dry inside, and then heat the section containing the
magnesium as strongly as possible. It is rather difficult to
get the magnesium to catch fire, and it may be necessary to
stop the water boiling in the flask for a moment, because the
steam cools the magnesium below its kindling temperature.
As soon as the magnesium catches fire pass steam rapidly
through the tube. Slip a test tube full of water over the end
of the delivery tube. Notice that the magnesium appears to
burn in the dry steam with much the same brilliancy as in air;
that a white smoke and ash (magnesium oxide) is produced
as in air. The blackening of the parts of the glass that were in
contact with the melted magnesium or its vapor may be dis-
regarded as far as the purpose of this experiment goes; it is
due to a reduction of the silicon dioxide of the glass to silicon.
The gas collected in the test tube is found to burn with a color-
less flame and is thus shown to be hydrogen.
(c) Magnesium amalgam is an alloy (much like a solution)
of mercury and magnesium. It is made by rubbing powdered
magnesium and mercury together in a mortar. Considerable
rubbing is necessary, because the oxide film on the surface of
the metal has to be rubbed off before the mercury can begin
to dissolve the metal. When the amalgamation once begins,
a good deal of heat is produced and the process is soon finished.
A semi liquid or a stiff amalgam is obtained, according to the
proportions used.
Drop a small lump of magnesium amalgam into a test
tube of cold water. A violent reaction takes place. A gas