near Midlan, Idaho, with Crystallo graphic notes. 409 



dull on exposure to the atmosphere for a few weeks. While 

 the outside of the nodule is a reddish-brown, the fresh fracture 

 reveals an iron-black color and a very compact cryptocrystalline 

 structure. The streak is chestnut- brown ; hardness, 55; spe- 

 cific gravity, 8*56 ;* opaque ; brittle. Before the blowpipe, on 

 charcoal, in the oxidizing flame, it decrepitates and fuses at 1, 

 with boiling and spirting, yielding a globule of lead, which, on 

 further heating, coats the coal yellow. It is easily soluble in 

 cold, dilute HC1, giving off chlorine. 



An analysis of an apparently pure fragment gave the writer 

 the following results : 



Lead _ r 83'20 



Silverf . trace 



Copper - 14 



(Fe, Al) _. 1-20 



Oxygen 12-93 



Insol. residue ... - 82 



Total 98-29 



.Neglecting impurities, and calculating to 100, we have 



Lead _ 86-55 



Oxygen 13-45 



Total 100-00 



Calcium and magnesium, in appreciable quantities, were 

 found both in the qualitative and quantitative analyses ; but 

 they were not estimated. The oxygen was determined directly 

 as H 2 0, by passing H over the powdered mineral, heated in a 

 combustion tube at low red heat, the H 2 being caught in a 

 series of calcium chloride tubes. 



The specific gravities, as given by BreithauptJ and Wheeler, § 

 for the natural lead di-oxide, are higher than is required 

 by its constitution ; and, until the investigation by Kinch, 

 the high specific gravity was cited as sufficient ground 

 for doubting the authenticity of the species. That given 

 by the Messrs. Hawkins || was as much too low. This, 

 however, may be accounted for in the fact that their analyses 

 show nearly 10 per cent, of impurities in the material analyzed 



* The specific gravity was carefully determined in a pycnometer with attached 

 thermometer, the mineral (3-1815 grams) being reduced to minute fragments, and 

 the air being pumped from it. Determinations of the specific gravity, made, with 

 the Jolly balance, on two other fragments, gave 8 - 35 and 8*86, the latter being on 

 a very small fragment. 



f 4 - 6463 grams of plattnerite yielded a silver button weighing 00022 grms. 



i 9-392 and 9-448. §9-411. 



|| 7-25 (" the mean of three close determinations"). 



