i! 
HANDLING SMALL AMOUNTS OF MATERIAL; SUBLIMATION 291 
of a hot stage such as that described on page 222 or by the method 
recommended by A. W. Blythd A small porcelain crucible is 
nearly filled with mercury, into which dips the bulb of a ther¬ 
mometer. A thin cover glass, bearing at its center the material 
to be tested, moistened and dried as usual, is 
floated on the surface of the mercury. Upon 
the cover glass is placed a low glass cell whose 
upper and lower rims are accurately ground. 
A second cover glass is placed above to receive 
the film — see diagram. Fig. 151. A number 
of clean covers should be placed near at hand. 
The crucible is heated over the low flame of 
a Bunsen burner. As the temperature rises, 
the covers are changed, by means of a pair of 
forceps, every five or ten degrees. The cover 
glasses are examined under the microscope, 
and a decision made as to the temperature of ^si- Crucible 
1 4 j j 4.U* j Method of Micro- 
subhmation. A second and even a third ex- ... 
sublimation. 
periment should always be made. If the 
material fails to sublime at a temperature below that at which 
the mercury itself is volatilized, a bath of a suitable low-melting 
alloy must be used. For accurate measurements it is essential 
to protect the crucible and cell from the cooling effects of air 
currents. 
Subliming upon a glass object slide as shown in Fig. 150 is 
impracticable when only a minute quantity of the material is 
available since the losses through incomplete condensation are 
considerable. In such an event it is safer to employ the device 
shown in Fig. 153, page 293, primarily intended for distillation 
but yielding good results with solids as well as with liquids. 
When, however, only an excessively small amount of material is 
to be tested as in toxicological analysis, it is better to drop the 
substance into a thin-walled glass tube of not over i millimeter 
in diameter, sealed at one end. Tap the tube gently so as to col¬ 
lect all of the material at the sealed end. With a very fine blast- 
lamp flarne draw out the open end to a hair-like capillary tube, 
^ Poisons: Their Effects and Detection, 259, 4th Edition, London, 1906. 
