to the first-named mercuric salt, and that such precipitates are of a pale yellow colour, which is in striking contrast to the full red colour which the precipitate would exhibit were neither of these organic substances present, since this precipitate would be iodide of mercury alone.

Continuing my researches in this field, I have ascertained that there is another class of organic bodies, besides alkaloids and albumenoids, which determine a yellow colour to the precipitate, which is formed when aqueous solutions of mercuro-iodide of potassium and mercuric-chloride are mixed, and this is that of the essential oils. I therefore hasten to inform you of this fact, and to acquaint you with a knowledge of the means which I find may be used to discriminate, for toxicological purposes especially, the mercurial precipitates so coloured, from those which are coloured by the presence therein of an alkaloid or an albumenoid.

The yellow mercurial precipitates, which are formed by this means in presence of these oils, volatilize entirely when gently heated, and their sublimates preserve their yellow colour, even when kept cool a long time. This reaction distinguishes such precipitates from those which are formed in part of a fixed alkaloid, also of an albumenoid; while from those formed in part of a volatile alkaloid they are distinguished by not reddening when treated with mercuric-chloride.

I find that a very minnte quantity of any of these oils is effective for the production of the phenomena I have described; for instance, one part of lemon oil to 10,000 parts of water will produce it.

The nitro-oils behave in this case in the same way as the essential oils. The nature of the mercuro-precipitate, which is thus formed in presence of an essential oil, I am unable as yet to determine for lack of time.