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NATURAL-PHILOSOPHICAL COLLECTION^. 



On a Singular Crystalline Vegetation of the Proto-nitrate of Mercury. • By 



W. B. O'SiiAUGHNESsy, M. D As far as I am aware, the peculiar mode of 



crystallization to which the subjoined observations are devoted, has not yet re- 

 ceived any particular notice. My attention was first directed to the subject, by 

 the inspection of a mass of proto-nitrate of mercury, prepared by Mr. Smith of 

 Lothian Street, as the preliminary step to procuring the acetate of that metal- It 

 presented a strange and very peculiar appearance, a confused arborescence having 

 taken place on the surface of the mass, consisting of multitudes of stalks con- 

 torted in various forms, and each bearing a particle of metallic mercury on its sum- 

 mit. In many places these productions assumed the aspect of the young fronds 

 of fenis, being rolled up spirally in that particular manner : in others, they lay 

 twined together horizontally like knots of worms ; but, altogether, froxn the quan- 

 tity of the mass and the number of the vegetations, I was much perplexed at the 

 time to discover an explanation of the circumstance. 



Since then, however, having had occasion to show my classes the method of pre- 

 paring the acetate of mercury, (of the Ed. College,) with very minute quantities of 

 the respective ingredients, I employed a watch-glass {ww in the subjoined engrav- 

 ing) for the formation of the proto-nitrate. P'or this purpose, a globule of the metal, 

 the size of a moderate grain of shot, was immersed in ten drops of nitric acid ; when 

 the action ceased, a particle as large as a pin's head remained undissolved in the 

 centre of the glass. In a few minues the spontaneous crystallization of the proto- 

 nitrate (already familiar to all pharmaceutical experimentalists,) took place, produc- 

 ing a white laminated mass, (w n,) retaining nitric acid in its interstitial spaces, and 

 bearing the undissolved globule of mercury on its upper surface, whither it was ele- 

 vated by the insinuation of the crystalline laminae from beneath. Having laid this 

 aside for use next day, I found, in the evening, that an erect round stalk had shot 

 up in the centre from the surface of the crystals, and bore on its top the drop of the 

 metal, at the height represented in the engraving when intersected by the line 



(o.) Next morning it had curled 

 downwards again, still retaining 

 the mercurial globule at its extre- 

 mity, which now rested at {b,) and 

 formed a complete arch. Next 

 day fresh growth had taken place, 

 the mercury again superior, when 

 it finally ceased, and now remains 

 at the elevation (c.) The speci- 

 men has now continued a fortnight 

 in this situation, and the mercury 

 remains perfectly bright, being seated in an hemispherical cup of the crystallized 

 proto-nitrate at the extremity of the stalk. 



. • Dr. Wollaston shewed, a long time ago, that a metallic blade dipped into 

 an acid or into a saline solution, does not undergo the same changes when sus- 

 pended free from contact, as when it is touched by another metallic substance 

 that is also immersed in the li(juid. If, for example, we hold a thread or lamina 

 of zinc in diluted sulphuric acid, a very slight chemical action is perceived ; if 

 we immerse, at the same time, a blade of platina or silver, the phenomenon re- 

 mains the same, and the new metal undergoes no change. But if we establish 

 a communication between the metals, out of the fluid, the chemical action be- 

 comes very marked, — globules of hydrogen are delivered from the platina or 

 silver, and the zinc oxidates with still greater rapidity. The same experiment 

 may be made with plates of copper and zinc, and, generally speaking, any 

 metal, tliougli it should have no effect on the fluid in which it is immersed, can 

 take on action when brought in contact with another metal. 

 The curious kinds of vegetation known by the names of trees of Saturn, trees 



