412 Transactions.— Chemistry. 
Art. LXV.—On the Nature of the Precipitate formed by certain Mercurie 
Salts in presence of Essential Oils. By Wmm Sxey, Analyst to the 
Geological Survey Department of New Zealand. 
[Read before the Wellington Philosophical Society, 21st February, 1880.] 
In a paper read before you last year* I showed that mercuric-chloride, 
when added to a mixed solution of mercuro-iodide of potassium and any 
essential oil, determined a white precipitate therein in the place of that red 
coloured one which would form were the oil omitted; but while I showed 
how these precipitates could be distinguished from those produced by such 
mercurial salts in the presence of the alkaloids and the albumenoids, I did 
not inform you as to the precise nature of these precipitates, being then 
ignorant of it myself. Since then, however, I have, in order to settle this 
point, acquired a wider knowledge of the whole matter, and so am enabled 
to inform you that other substances, not exactly essential oils but partaking 
somewhat of their nature, also behave like such oils in respect to the 
mercurial compounds named; and by this wider knowledge of the subject 
I am also enabled now to describe the nature of these precipitates to you. 
These substances are camphor, carbolic acid, kerosene, gasoline, picro- 
toxia, and guaiacum resin. à; 
In regard to kerosene and gasoline it is only a very small portion of 
these substances which is ever concerned in the production of any colourless 
mercurial precipitate; and so I consider this part to be a portion of the 
oil which has been oxydized by the air to an acid hydrocarbon, or to some- 
thing on the way to this. 
And now, as to the nature of the precipitates :— 
Camphor.—As I have got that obtained in presence of camphor,—none 
of the camphor is present. I merely decanted the liquid portion off, and 
allowed the residue to dry in the air ata low temperature. The pale yellow 
mass thus resulting turned to a bright scarlet colour when pressed, as the 
iodide of mercury does, but kept its yellow colour for months ; 
indeed, it would do this permanently, if left alone. As this yellow mass 
does not contain camphor, it is certainly the pure mercurial iodide; and 
the reason, therefore, that it does not (as it is termed) spontaneously 
redden, is that its particles are so detached among themselves that, except 
for some outside agency, they cannot get sufficiently within each other's 
influence to favour the molecular action necessary to produce this change 
of colour. 
Guaiacum Resin.—This resin, in acetic acid diluted with water, furnishes 
& solution which, like the other oils and resins named here, does not afford 
a precipitate with mercuro-iodide of potassium, but when afterwards treated 
* Trans. N,Z. Inst., Vol. XL, p. 470, 
I may say, 
