412 Transdctions. — Chemistry . 



Art. LXV. — On the Nature of the Precipitate formed by certain Merc^iric 

 Salts in presence of Essential Oils. By William Skey, Analyst to the 

 Greological 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 Avould 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 uatm-e, 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. 



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 obtamed in presence of camphor, — none 

 of the camphor is jpresent. I merely decanted the liquid portion off, and 

 allowed the residue to dry in the air at a 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 ; I may say, 

 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 

 a 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, 



