ON MICRO-SUBLIMATION. 
417 
for instance, to be a very successful result of a toxicological procedure if the 
80th of a grain of cantharidine were obtained and recognized as such by its 
action on some sensitive portion of the skin ; but he had found that of a 
grain yielded excellent results by the method of sublimation. We might take 
the t Lq grain of the powder of cautharides, which, according to the general state¬ 
ment, contained ‘4 per cent, of cantharidine, and get from that small portion 
one, two, or three excellent sublimates ; the first would show the characteristic 
form which cantharidine always puts on when sublimed; the second or third 
might be a little indistinct, but it was only necessary to touch them with a 
drop of ether, when the sublimate would dissolve and deposit the characteristic 
crystals. This method, therefore, afforded a characteristic test, far exceeding 
in delicacy that commonly employed. To take another example : there was a 
liquid in use by gunsmiths for browning gun-barrels, consisting of a mixture of 
corrosive sublimate, tincture of muriate of iron, some salt of copper, and spirits 
of wine. If we took a drop of that liquid and allowed it to crystallize on a 
glass slide, we could not say what the crystals were; but, on applying heat, the 
corrosive sublimate would be driven off and deposited in its characteristic form. 
If there were any doubt about it, it was only necessary to touch it with a drop 
of one of its characteristic reagents, and certainty would be at once obtained. 
There was then left a deposit which, on being treated with ammonia, yielded 
the i*eaction of a salt of copper ; and this being washed off, the residue would 
be found to give the reactions of a salt of iron. It was very advantageous thus 
to separate the volatile from the non -volatile constituent of a compound fluid. 
He could not but hope that when, instead of having one or two labourers in 
this fruitful field, they had many, very important results would be obtained. 
Sublimates, when obtained, were in so pure a state that their reactions were 
eminently satisfactory. Supposing they had the xoooo a grain of strychnine 
to operate upon, they would be more likely to obtain satisfactory results by 
sublimation than by acting upon it in the ordinary way, and it did not prevent 
the subsequent application of the liquid tests ; and having the substance 
sublimed on to a glass disk, it was in a very convenient form for examination 
by the microscope. In conclusion, he would allude to what might perhaps prove 
to be a very important subject—the different temperatures at which sublima¬ 
tion took place in different bodies. He believed that when investigations of 
this nature had been more fully carried out, they would be able to distinguish 
by the aid of heat alone a great number of different substances with perfect 
certainty, or, at all events, a very important link in the chain of reasoning as to 
the article under examination would be supplied. For instance, strychnine was 
found to sublime at 435°; if they found, therefore, that a substance sublimed 
at this temperature, there would be a strong presumption that it was strychnia 
they were dealing with. Strychnia also yielded a sublimate of a very definite 
character, not standing quite alone, but very nearly so, and when a still greater 
degree of heat was applied, it gave a deposit of carbon. If all these characters 
were combined in the case of any substance under examination, there could be 
scarcely a doubt of its being strychnia, but there still remained the power of 
applying the characteristic liquid tests in order to be absolutely certain. He be¬ 
lieved the same was true of many other substances ; and, in the paper just pub¬ 
lished in the Society’s Journal, he had shown that by the test of heat and subli¬ 
mation the active poisons, organic and inorganic, might be thrown into several 
well-definel groups. 
Professor Attfield said the researches of Drs. Helwig and Guy and Mr. 
Waddington opened out a large and very important field for research, but what 
was stated was not altogether new. More than half of the substances which 
had been mentioned that evening as yielding sublimates had long been known 
to be volatile; though others, which had been regarded by chemists as fixed, 
"VOL. IX. 2 E 
