22 THE ELEMENTS.
perature remains constant for from 10 to 20 minutes. In deter-
mining this temperature, a supercooling occurs regularly; i.e.,
the thermometer at first falls a few degrees below the solidification
point while the mass still remains perfectly liquid. Then, as the
crystals of the solid begin to separate, the temperature rises
rapidly to the solidification point, where it remains perfectly sta-
tionary while the mass is crystallizing. After this point is deter-
mined, increase the flame a little and find the melting-point in an
exactly corresponding manner. Tin melts at 232° C.
In using a long, ordinary thermometer the observed tempera-
ture is always a few degrees too low because the entire thread of
mercury is not at the desired temperature. Such an observed
reading gives the " unconnected melting-point." It may be cor-
rected by adding the value, 0.000,16 • a (t — t 0 ), in which a is
the length in scale degrees of the exposed thread of mercury, t
is the observed reading, and U the average temperature of the
exposed mercury. This last value is obtained by a second ther-
mometer, the bulb of which is placed at about the middle of the
exposed mercury column. The correction is usually spoken of as
the "correction for stem exposure." Another method for applying
the correction for stem exposure has been proposed by E. Rim-
bach;
1
see also Preparation No. 49.
- Pure Antimony from Basic Antimony Chloride.
Basic antimony chloride (antimony oxychloride) is a by-
product in the preparation of antimony trichloride (No. 47).
Grind the dry basic chloride with twice its weight of powdered
potassium cyanide, and heat the mixture in a porcelain crucible
over the blast lamp. To prevent loss of heat by radiation, sur-
round the crucible with a piece of iron stovepipe, a flowerpot,
or a larger graphite crucible, the bottom of which is cut off. After
cooling wash the metallic regulus with water until all the adhering
slag is removed. The antimony has a silver-white appearance
and shows a crystalline structure.
Regarding the density of antimony, see page 16. Dependent
preparation, No. 88.
1
Ber. 23, 3072 (1889).