SxEv.— Precipitates of Mercurie Salts with Essential Oils. 413 
with mercuro-chloride, a pale one forms, of some permanency as to colour. 
This compound, however, differs from the others which I have described in 
being of a soft plastic nature. It passes through filter-paper as readily as 
the analogous compound with digitaline. It reddens under pressure—a 
singular circumstance, considering that a resinous matter is certainly pre- 
sent throughout it, and as it seems, combined therewith. That a purely 
mechanical force, as pressure, can not only modify the chemical (or, at 
least, molecular arrangement) of a substance like mercuro-iodide,—but 
actually eliminate a substance (and one which is, besides, non-volatile at 
the temperature used) from its combination with this salt (mercuro-iodide), 
in order to pass such mercuro-salt to its more fixed or final form,—would 
be a phenomenon of so unexpected a nature, that one hesitates to accept 
this view of the case, and feels inclined, for the present, to consider the 
colorific change in question to be favoured by a decomposition of the pre- 
cipitate prior to its being dried for the pressing. Urea behaves with these 
mercurial salts much the same as this resin. 
Carbolic Acid.—The compound formed by these mercurial salts in pre- 
sence of this acid, appears in the form of opalescent oily globules, which 
neither subside nor are retained by paper-filters ; however, by the addition 
thereto of a little common salt, these agglomerate and finally precipitate 
in the form of a light yellow solid, which when dried preserves its colour 
even when strongly pressed by a hard substance ; it also sublimes without 
undergoing any notable chemical change, and the sublimate is also un- 
affected by pressure. From these results it appears that the pale precipitate 
in question contains carbolic acid, and is a compound possessed of consider- 
able stability. 
Picrotoxia.—Picrotoxia, by the process described, forms a compound with 
mercuro-iodide having considerable stability; its colour is not affected by 
pressure ; it is not chemically affected except at a comparatively high tem- 
perature, in which case it chars and evolves gaseous matters. 
I need not detail any further results, as the cases I have selected for 
this are typical of all I have investigated. I will only refer back to the 
precipitates formed in presence of the more volatile substances cited, for the 
purpose of stating my belief that as the less volatile oils certainly combine 
with the mercuro-iodide, the more volatile ones in the first instance are also 
in combination with it, but a combination so unstable that it is difficult to 
isolate them for examination. 
I should state that these mercuro-compounds are, as a rule, soluble in 
alcohol, ether, mercuro-iodide of potassium, or mercuric-chloride. : 
These results show that in examining for albumenoids or alkaloids by 
the mercuro-iodide and chloride test, it is necessary to remove all resinous 
