ON MICRO-SUBLIMATION. 
411 
that many alkaloids sublimed in round granules is hardly correct. A sublimate, 
consisting of round granules, is more or less common to all organic sublimates. 
It is a modification which I believe admits of explanation, but at present I have 
been unable to investigate it. If the process is cautiously continued, the round 
granules generally disappear. Crystalline sublimates, more or less defined and 
typical, taking their place. This will be observed in many slides where the 
process has been stopped before the whole of the granules have disappeared. I 
am convinced that their production depends in some measure upon the heat of 
the receiving glass; the most perfect crystals are obtained when no granules 
appear, but if the glass becomes too hot these crystals melt, and the granules 
again form. 
Much doubt has existed as to whether the sublimates were identical in com¬ 
position with the original substance. The sublimate of strychnine was identical 
with that substance itself, both as to its crystalline form, and also to its 
behaviour with various chemical tests; and although the fact of one or two 
alkaloids subliming unchanged cannot be taken as a proof that others will do 
the same, yet when coupled with the knowledge that perfect sublimates were 
obtained from nearly every alkaloid operated on, it affords strong grounds for 
supposing that they do. The fact that one or two alkaloids yielded no definite 
sublimate can hardly militate against this, as I have every reason to think that 
these may be sublimed when the heat is more effectively applied. 
I think that by the method I shall describe, it is probable, nay more, almost 
certain, that during some part of the process perfectly typical crystals of the 
substance operated on may be obtained, and that from quantities not exceeding 
the g’oth of a grain ; for, as a rule, the smaller the quantity the better the result. 
Thus in submitting the -^th of a grain of any sublimable substance to heat, the 
first sublimate will perhaps possess little distinctive feature, the second will be 
better, and so on until the substance is nearly dissipated, when the crystals will 
generally be most perfect. Notwithstanding this, I must acknowledge that the 
variety of form occasionally produced on the sublimates, precludes at once any 
certain definition of their nature from the crystalline appearance. It may 
suffice to mention that I have obtained sublimates of codeine, strychnine, and 
santonin, so identical in form, that had they not have been labelled, it would 
have been impossible to separate the one from the other. The apparatus I have 
used consists of a spirit-lamp, a piece of thin iron plate, and a few glass rings. 
Three straight lines should be marked on the plate, one across the centre, the 
others an inch and a half on either side of it. This will be found of great use, as 
the centre of a slide is at once shown. There should be the merest possible 
curve in the centre of the iron plate, so that when a glass slip, 3 inches Jong, is 
laid upon it, the centre does not touch by the £ or a of an inch. This has the 
decided advantage of never allowing the glass holding the substance to come 
into actual contact with the iron plate, thus modifying the heat considerably. 
I have entirely discarded the use of thin glass for receiving the sublimate, for 
two or three reasons. As a rule, much better sublimates are obtained upon hot 
than upon cold glass, and on account of the small bulk of the circles of thin 
glass they cool too rapidly. They are inconvenient to use, as they cannot be 
manipulated by the fingers alone; and when the sublimate is upon a slide, it is 
much more convenient for examination, and, if necessary, for applying liquid 
tests. In subliming arsenious acid, for instance, I can never obtain such good 
sublimate upon the thin glass as upon the slide itself. Very long directions have 
been given for obtaining sublimates of arsenic, but, with two pieces of glass and 
a glass ring, sublimates of arsenic may be obtained which cannot be surpassed. 
A ring is placed on a glass slip, a minute quantity of arsenic put into the 
centre of it, and the slip placed on the iron plate before mentioned, and heat 
applied. When the arsenic begins to sublime, another piece of glass, which has 
