84 Capt. P. Yorke's Experiments and Observations 



perfect rhombic dodecahedrons, and others of the same funda- 

 mental form with the acute solid angles replaced by tangent 

 planes : they varied in diameter from about g-^th 

 to T tf£o tn °f an mcn * When heated, these cry- 

 stals become opake and orange-coloured, but 

 without losing their form or brilliancy of surface. 

 Houton Labillardiere*, it is said, obtained do- 

 decahedral crystals of the anhydrous protoxide as a deposit 

 from a solution of oxide of lead in a solution of caustic soda; 

 and Becquerel has obtained cubes by heating the oxide with 

 pure potash f. 



9. Lead, as it occurs in commerce, it is well known, gene- 

 rally contains portions of copper and iron. I found on trial 

 that the lead I had used did contain those metals, (it contained 

 no silver,) and traces of copper could even be detected in the 

 grey crystals of oxide, when they were fused with borax be- 

 fore the blowpipe in the reducing flame. Lest the action of 

 water and air described should be in any way dependent on 

 these alloys, I attempted to procure a quantity of the metals 

 quite pure to repeat the experiments on. 



10. Nitrate of lead was recrystallized, till the mother liquor 

 gave no trace of copper on the addition of carbonate of am- 

 monia, and the oxide resulting from the calcination of this 

 nitrate was reduced by black flux in a Hessian crucible. It 

 was then kept in fusion for some time at a low red heat in a 

 Wedgwood crucible to separate any carbon it might contain. 

 The lead thus obtained yielded, however, a very slight trace 

 of iron, — derived, I believe, from the action of the flux on 

 the Hessian crucible, — but none of copper. A bright slip of 

 this lead was treated with distilled water as before ; the effects 

 were similar : the white crystalline substance formed first, and 

 after about a month, the brilliant grey crystals of anhydrous 

 oxide were formed ; they had, perhaps, less of a green shade 

 of colour than those formed on common lead. 



11. In a quantity of a solution of oxide of lead in lime- 

 water, which had been left a year in a flask stopped by a 

 cork, some brilliant crystalline folia had formed about ^ an 

 inch across, dependent by their upper edges from the surface 

 of the liquid ; they were very thin, flexible and elastic. By 

 reflected light, their colour and lustre resembled that of steel 

 blued by heat. They dissolved quietly in acetic acid, became 

 yellow when heated, and appeared identical with the crystal- 

 lized laminae before described — anhydrous protoxide (8). 



12. A bright iron nail was driven into a clean slip of lead, 



* Berzeliu*, torn. Hi. p. 178. f Ann. de Chimie, torn. li. p. 104. 



