70 PROVOSTAYE ON THE ACTION OF 
On continuing to apply heat, the substance sublimes. This 
happens near the boiling point of mercury, but this point has 
not been exactly determined. In every instance it distils without 
alteration, and condenses perfectly white and pure, very close 
to the heated portion of the tube. The colour of this substance 
changes rapidly with its temperature. When distilling, it is 
nearly as red as liquid hyponitric acid. At about 220° or 230° 
cent. (428° or 446° Fahr.), the liquid is yellow, possessing an 
oleaginous appearance, both in consistence and colour. Shortly 
after solidification, when it becomes opake, it acquires a very 
fine canary-yellow colour. This tint becomes paler, and at a 
low temperature the substance is presented in brilliant white 
silky tufts. By means of a microscope, the crystalline form is 
perfectly visible. In general, the crystals seem to be finer and 
more distinct in proportion to the rapidity of cooling. They 
appear to be rectangular four-sided prisms P, two opposite sides 
Fig. 2. being truncated by a pair of faces T 
(fig. 2.). It is seldom that the summits 
of these flat and very elongated prisms 
can be distinguished. In one case, how- 
ever, four or five adjoining crystals were 
discovered, the summits of which were 
well defined; the two sides A B and 
B C forming aright angle. For the re- 
mainder, it was impossible to distin- 
guish whether their extremities were 
composed of two or four faces. We 
shall afterwards revert to this crystalline 
form. 
To make an analysis of this substance, it is necessary to 
transfer it to another tube. This operation is accompanied with 
some difficulty, if the absorption of water is to be entirely pre- 
vented ; it may, however, be performed without risk in the fol- 
lowing manner. Fuse a small portion by means of a lamp, and 
cause it to flow into the drawn-out beak of the tube which con- 
tains it*; then break the point and direct it into a small well- 
dried tube previously weighed. Apply heat; the liquid flows 
from one tube into the other. When all the separated portion 
* This substance, when anhydrous, may be fused and volatilized in a sealed 
tube without danger, but that is not the case when it contains water. 
