form in the substance, or a mist upon the disk. We may miss the precise moment of the change, and make too high an estimate of the temperature. Such errors of observation have been guarded against, in the case of the results presently to be detailed, by repeating the experiment several times with the same substance. Proceeding thus, I have rarely found occasion to correct my first entries of results; and I believe that the method will be found to yield approximations sufficiently close for every practical purpose, if we only adopt the simple and obvious precaution of not attaching importance to differences of a few degrees between the melting or subliming points of two poisonous substances. If, for instance, we experiment with a substance which melts at 220°, and assume it to be codeia, it would be a valid objection that paramorphia and papaverine melt at 210°. So also with aconitia and atropia. A temperature of 140° would not justify us in assuming that we are dealing with aconitia, seeing that atropia melts at 150%. But if we suppose that a minute quantity of a white powder is placed in our hands, and that it sublimes at 210°, we know that it cannot be veratria, which melts at 200°, or paramorphia or papaverina, which undergo the same change at 210°, or codeia, 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 leading sets of phe

nomena :

1. Sublimation without change of form or color.

2. Sublimation without change of form or color, followed by melting, with or without change of color and further sublimation.

3. Melting and change of color, 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 Color.-This class comprises corrosive sublimate and calomel, arsenious acid and cantharidin, which, if the heat is gradually increased, and then maintained at or near the temperature indicated, are gradually dissipated in white vapor, 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 substances 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 cantharidin, which, as the heat is usually applied, first melt, and then disperse in white vapor, leaving also no residue. The subliming temperatures of the four poisons are as follows:

Corrosive sublimate, at or about

200° Fahr.

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 microscope at this temperature. To obtain large sparkling crystals a higher temperature is required. I have also obtained sublimates in several reduction-tubes immersed in a sand bath side by side with the thermometer at a temperature 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 low figure of 370°. All these figures much exceed the temperature indicated in my own experiments; and, as the small quantities which I employed 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 reductiontubes, I used fragments of solid arsenious acid, none, of which could have exceeded a grain in weight.

If this first group were enlarged so as to embrace substances

which yield sublimates resembling somewhat those of one or other of its members, it would include 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 dissipated in white fumes.

2. Sublimation without Change of Form or Color, followed by Melting with or without Change of Color and with further Sublimation. This class includes the three poisons-oxalic acid,morphia and strychnia. The first (oxalic acid) sublimes, then melts, and is dissipated without residue. The second and third (morphia and strychnia) first yield sublimates, then melt and darken, continue to sublime, but leave a distinct layer of carbon. These changes take place at the temperatures indicated below:Oxalic acid sublimes at or about 180°, melts at or about 280°

3. Melting, Change of Color and Sublimation.-This class comprises all the poisonous alkaloids and glucosides, except the members of class 2,-morphia and strychnia. Their melting and subliming temperatures are given below, arranged in the order of their melting temperature, beginning with the lowest : Aconitia melts at or about 140°, sublimes at or about 400°

I add a statement of the melting and subliming temperatures

of the members of the opium-series :—

Meconina melts at or about 120°, sublimes at or about 180°

Codeia melts at or about 220° sublimes at or about 220°

All these substances, it need not be stated, yield, like morphia and strychnia, a more or less abundant carbonaceous residue, by which the alkaloids and glucosides are distinguished from most other bodies. To these distinctive characters that of giving out a marked odor, in some cases agreeable, in others offensive, ought to be added. As the result of repeated careful experiments, both with platinum-foil and the porcelain slab, I give the following:-Strychnia, pleasant but not easy to describe; morphia and atropia, as of singeing; brucia, as of burnt horn; aconitia, not disagreeable, but ill-defined; veratria, mousy and irritating to the nostrils; digitalina, as of the drug; solania, as of roast apple.

On comparing class 2 with class 3, it will be obvious that, with common care in applying heat, it would not be possible to confound the two important alkaloids, morphia and strychnia, with any other known poisons. A white powder or crushed crystal, which first sublimed at 330°, or from that to 345°, melted at some higher temperature, and continued to yield sublimates till it left a final carbonaceous deposit, must be either morphia or strychnia. If both changes happened at the lower temperatures indicated in the table, it would be morphia; if at the higher, strychnia. The peculiar white disks developed in the sublimate are common to the two alkaloids, and the forms of the sublimates might also not prove characteristic. Hence it might be necessary to resort to the color test or the carbazotic-acid test, to render the diagnosis certain. A glance at the tables will show that many of the alkaloids or glucosides melt and sublime also at temperatures so low as not to admit of being confounded with either of these important poisons.

It will be observed that some of the poisons in class 3 (digitalina, picrotoxia, and solania, in the first group, and codeia and cryptopia, in the second) have appeared to melt and sublime at the same temperature. They have seemed to melt and then sublime, with a scarcely appreciable interval. As there is not apparently even the small difference of 10° shown in the case of

morphia, they have been grouped as above.

Of solania it may be stated that it darkens, and grows almost black, before it melts.

I will now give brief notices of other experiments made with the apparatus above described, and then bring the paper to a close by presenting a tabular form, embracing the principal poisons which we encounter as white powders or colorless crystals.

1. Oxalate of ammonia yields sublimates at 280°, and is wholly dissipated by heat.

2. Binoxalate of potash yields sublimates at 280°, and leaves a white ash.

Camphor sublimes at 150°.

Cyanide of Mercury begins to sublime at 320°.

Oxide of antimony sublimes slowly and scantily at 480°. Tartar emetic decrepitates at 380°, sublimes slowly and scantily at 480°, and chars at about 550°.

Sulphur melts and sublimes at 180°.

The volatile metals crushed into coarse powder sublime as follows::

1. Sublime without change

Table showing the approximate results, for the principal poisons, of sublimation at ascertained temperatures:

of form or color, yielding Corrosive sublimate

white vapor.

Temperature.

Sublime.

2000

Cantharidina
Calomel

2120

2400