3dly. It is more usual for the prism to have eight sides by truncation of each of its angles, and at each extremity eight additional surfaces occupying the place of the eight linear angles between the prism and terminating pyramid of the 2d variety. The complete crystal has then thirty-two sides.
4hly. The eight surfaces last mentioned, as interposed between the prism and pyramid, are sometimes elongated into a complete acute pyramid having eight sides arising from the angles of an octahedral prism.
The 3d form above described, corresponds so entirely with that given by the Abbé Haüy as one of the forms of the hyacinth or jargon, that I have little reason to regret my inability to obtain chemical evidence of the composition of these crystals.
Those, and other impurities, I usually separated, as far as was practicable, by mechanical means, previously to forming the solution of platina, which has been the principal object of my attention.
§ III. Precipitation of Platina.
When a considerable quantity of the ore had been dissolved, and I had obtained, in the form of a yellow triple salt, as much of the platina as could be precipitated by sal ammioniac, clean bars of iron were next immersed in the solution for the purpose of precipitating the remainder of the platina.
For distinction it will be convenient to call this, which in fact consists of various metals, the first metallic precipitate.
The treatment of this precipitate differed in no respect from that of the original ore. It was dissolved as before, and a portion
- Traité de Mineralogie, Pl. XLI. fig. 17. -- Journ. des Mines, No. 26, fig. 9.