412 
PHARMACEUTICAL MEETING. 
been laid on the iron plate or allowed to become warm by any other means, is 
placed over it to receive the sublimate, the glass ring being its only support. 
If the glass slip be hot enough, the arsenic will sublime in regular octahedral 
crystals, not at all crusted, but leaving a good margin between each crystal. If 
the result of the sublimation, owing to the glass being insufficiently heated, is 
crusted, it should be rapidly wiped off and returned to its place, and this process 
may be repeated until a satisfactory result is obtained. The glass, by this 
means, continually increases in heat, each successive sublimate being an im¬ 
provement on its predecessor. It may be thought somewhat unnecessary to give 
such a detailed account of the sublimation of arsenic, a subject by this time 
nearly exhausted, but I have done so because it may be taken as the type of all 
other sublimates. The only modification of it consists, iu some substances 
having been mixed with powdered glass and then sublimed. Powdered glass 
possesses some advantages over sand, which was recommended in the case of 
theine by Dr. Stenhouse ; it is more easily cleaned, it can be obtained in a finer 
state of division, and on account of its perfect whiteness the least change of 
colour may be well observed. Its use is a great advantage in many, but not in 
all cases. 
The heat requires very carefully regulating, but as the iron plate is of some 
little size, different degrees of heat may be obtained by moving the slides to the 
right or left. The flame of the spirit lamp should not be immediately under 
the substance subliming, but a little on one side of it. I have tried the method 
of keeping the receiving-glass cool, by means of blotting-paper constantly 
wetted, but I cannot speak favourably of it. The great point seems to me to 
get the receiving-glass only a few degrees lower in temperature than the glass 
from which the substance is sublimed. 
A cold slide should never be placed to receive the sublimate after heat 
has been applied. It may be so before, but not after, and for this reason, that 
when a cold slide is approached to the subliming substance a portion of it is 
often attracted by it, possibly by the two glasses being in a different electrical 
condition. 
A somewhat curious feature is often observed in sublimation by this process, 
that many substances in subliming are deposited on the glass in curved lines, 
which at first present no crystalline appearance. As the sublimation proceeds, 
crystals form at all points of these lines. Morphia seems to have a tendency to 
sublime in this way ; I have obtained sublimates of this alkaloid consisting of 
nothing but curved lines, commencing at the segment of a circle, and progress¬ 
ing through subsequent stages, until a perfect figure 8 is obtained. For some 
time I could not but imagine that this was owing to the glass being imperfectly 
cleaned, and I accounted for the circular shape by supposing that the cloth used 
had become soiled, and that in the act of wiping circles had been described on 
the glass. This does not hold good for two reasons; first, the circular figures 
are so small as to preclude all possibility of their being hand-made; secondly, 
that upon one occasion, when endeavouring specially to guard against this phe¬ 
nomenon, I took care to wipe the glass from end to end, precisely the same 
result ensued. 
Many substances yield two sublimates, differing, I believe, only in form and 
not in composition. The second sublimate will be found as very thin platy 
crystals, perfect in shape, with the peculiar feature, that, instead of being 
attached to the slide superficially, they are pendent by a single angle. Owing 
to their extreme tenuity and their angular position, they decompose light con¬ 
siderably; so much so, that the field of the microscope is often entirely obscured. 
They may be removed with facility, by allowing another glass slide to touch 
them ; even if this rests upon them, they suffer little damage. 
For obtaining larger quantities of sublimates I find that the best method is to 
