320 Prof. A. H. Church — Specific Gravity of Precious Stones. 



steel by raising it to different temperatures. On examining the 

 altered iron, the author was enabled to detect the presence of a 

 small amount of the alloy termed plessite. The figures are in their 

 general characters identical with those developed by acid. When a 

 polished plate of the Charcas iron is plunged into a hot solution 

 of copper sulphate, the figures are developed with greater distinctness 

 than when acid is used, the lamellae of tanite appearing red on a 

 white ground. By employing mercury chloride and varying the 

 degree of concentration and temperature of the solution, a metallic 

 surface may be made to present as many as three different phases of 

 crystalline development. With a hot concentrated solution of this 

 salt the Charcas iron exhibits the most beautiful figures. Gold and 

 platinum chloride have also been used by the author, and the former 

 salt is recommended in cases where it is desired to arrive at an im- 

 mediate knowledge of the crystalline structure of an iron. 



To etch a fine section of Toluca iron, recently acquired by the 

 British Museum, water saturated with bromine was used. The 

 edge of the slab was surrounded with modelling wax ; the bro- 

 mine water was then poured on, and in a few seconds removed with 

 blotting paper. The surface was next flooded with distilled water, 

 which was removed as before. Absolute alcohol was then poured 

 over the etched surface, and this again was quickly taken away with 

 bibulous paper. The iron was then preserved face downwards for 

 some days in a dry box filled with burnt lime. Plate IX. gives a 

 representation of a part of the surface of this beautiful slab of metal. 

 The figures will be considered when we come to describe those of 

 the Braunau iron and the crystals of meteoric iron which occur in 

 the Cranbourne meteorite. 1 



(To be continued hi our next Number.) 



VI. — Notes on the Specific Gravity op Precious Stones. 

 By Prof. A. H. Church, M.A. 

 "T^KOM time to time I have accumulated a large number of results 

 Jj obtained in identifying precious stones by means of their 

 specific gravity. From these results I have selected about 70, which 

 will be found arranged below. The observations have been made 

 with care, and, where no temperature is given, at 15° 5 C. ; an 

 asterisk denotes those determinations in which a very accurate assay 

 balance by Oertling was used, and in which the specimens were 

 immersed in alcohol, not in water. In these latter determinations 

 any error would be confined to the third place of decimals. 



Remarks. Spec. Grav. 



Moonstone, flawless, Ceylon 2-585 



Brownish yellow, flawless 2 - 69 



Deep sky-blue, flawless (probably been heated)... 2 - 701 

 Yellow, became blue after ignition but unchanged 



in spec, grav 2697 



5. () Fine aquamarine, weighing 5 - 73 grams 2 - 702 



1 Kick (Pul. Notizbl. xxix. 105 ; Pol.'Jour. ccxii. 40) employs for the etching of artificial iron 

 and steel a mixture of one part of hydrochloric acid and one part of water, to which a little 

 antimony chloride has been added. Surfaces etched with this liquid are less liable to rust. Kick 

 states that some irons and steels are quite passive, but that this property may be destroyed by 

 raising them to a red heat. 



No. 



Name. 



1. 



2. 

 3. 

 4. 



*Adtjlaria 

 Beryl 

 >) 



