OF THE PRINCIPAL POISONS, ORGANIC AND INORGANIC. 373 
of a white powder is placed in our hands, and that it sublimes at 210°, we know 
that it cannot be veratrine, which melts at 200°, or paramorphine or papaverine, 
which undergo the same change at 210°, or codeine, which melts at 220°. The 
substance belongs to a wholly different group. It might be muriate of 
ammonia, which sublimes at 210°, or powdered cantharidine, which sublimes at 
212°, or even corrosive sublimate, which sublimes at 200°, either not melting 
at all, or melting at a higher temperature after subliming. 
These observations will have prepared the way for a classification of poisonous 
and other substances, which promises to be of practical diagnostic value. In 
performing these experiments in the manner indicated, we encounter three lead¬ 
ing sets of phenomena :— 
1. Sublimation without change of form or colour. 
2. Sublimation without change of form or colour, followed by melting, with 
or without change of colour and further sublimation. 
3. Melting and change of colour, followed by sublimation. 
I now proceed to arrange the principal poisons under these three heads, 
giving the results obtained with the apparatus as above described. 
1. Sublimation without change of Form or Colour .—This class comprises cor¬ 
rosive sublimate and calomel, arsenious acid and cantharidine, which, if the 
heat is gradually increased, and then maintained at or near the temperature in¬ 
dicated, are gradually dissipated in white vapour, and leave, if pure, no residue. 
This graduated sublimation, therefore, differs somewhat from the quicker 
process with the spirit-lamp and platinum-foil, which places the four sub¬ 
stances in two classes; the one containing arsenious acid and calomel, which 
do not melt, but are converted into white fumes, without residue ; the other 
corrosive-sublimate and cantharidine, which, as the heat is usually applied, 
first melt, and then disperse in white vapour, leaving also no residue. 
The subliming temperatures of the four poisons are as follows:— 
Corrosive sublimate, at or about. . . 200° Fahr. 
Cantharidine ,, ... 212° ,, 
Calomel ,, ... 240° ,, 
Arsenious acid ,, ... 280° ,, 
As this temperature of 280°, for arsenious acid, is very low compared to that 
commonly assigned (370° to 400°), I have carefully repeated the experiments 
with this poison, and find a distinct sublimate, showing crystals under the mi¬ 
croscope at this temperature. To obtain large sparkling crystals a higher tem¬ 
perature is required. I have also obtained sublimates in several reduction- 
tubes immersed in a sand bath side by side with the thermometer at a tempera¬ 
ture never exceeding 300° ; and some of these consisted of large sparkling 
crystals. On referring to works of authority, I find the subliming temperature 
of arsenious acid variously stated—by Miller and Bloxam at 380°, and in the 
British Pharmacopoeia at 400° (not exceeding 400°). Dr. Taylor places it at 
the lower figure of 370°. All these figures much exceed the temperature 
indicated in my own experiments ; and, as the small quantities which I em¬ 
ployed cannot account for the discrepancy, I am at a loss to explain it. I 
ought, perhaps, to state that, in the experiments with the small reduction- 
tubes, I used fragments of solid arsenious acid, none of which could have ex¬ 
ceeded a grain in weight. 
If this first group were enlarged so as to embrace substances which yield subli¬ 
mates resembling somewhat those of one or other of its members, it would in¬ 
clude muriate of ammonia, which sublimes at or about 210° Fahr., and yields a 
sublimate which might be confounded with the less defined forms of arsenious 
acid. The most successful sublimates of muriate of ammonia consist wholly 
of cubes. Sublimed from platinum-foil, it first crepitates, and is then dissi¬ 
pated in white fumes. 
