Skey. — Precipitates of 2Ien-uric 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 digitaliue. It reddens under pressm-e — 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 pressiu-e, 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 comj)Ound 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 httle 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 carbohc acid, and is a compound possessed of consider- 

 able stabihty. 



Picrotoxia. — Picrotoxia, by the process described, forms a compound with 

 mercuro-iodide having considerable stabihty ; 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 fhst 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 



