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

DISTILLATION. 7

If the vapors attack cork the apparatus can be made tight

with wads of asbestos fibers pressed into the joints, an expedient

which often yields excellent service.

For determining the boiling-point of the substance a ther-

mometer should be inserted in the neck of the distilling flask, or

Fig. 8.

in the tubulus of the retort, in such a way that its bulb will be

entirely surrounded by the vapors (Figs. 6 and 8); thus with a
distilling flask the bulb should reach to the lower part of the
neck. It is best to use thermometers so short that the mercury
column will remain entirely within the vapor. The thermome-
ter shows at the beginning a temperature somewhat too low

because some time is necessary to heat it to the temperature
of the vapor; toward the end the reading becomes a little too
high on account of the vapor in the nearly empty flask becoming
superheated. Both of these facts are to be borne in mind when

judging of the purity of a substance. Concerning fractional

distillation, which is seldom of importance in making inorganic

preparations, see the preparation of acid chlorides and esters,
Chap. VI.

For vacuum distillation, use an apparatus similar to that shown

in Fig. 6 on page 6. The rubber stopper of the distilling flask,

besides carrying the thermometer, should be provided with a