On the Composition of Avanturine-Glaaa, 



315 



pieces of avanturine, which were dissimilar in their external 

 aspect, though they varied a little in the proportions of their 

 constituent parts, still contained the same ingredients. The 

 mean of several analyses afforded the following composition in 

 the 100 parts : — 



99.0 



From this composition, we can only conclude that the arti- 

 ficial avanturine of Venice is an ordinary glass which owes its 

 colour and shining appearance to copper, and copper pro- 

 bably in the form of protoxide. However, the perfect opacity 

 of the extremely thin crystalline leaflets was against the last 

 idea. The microscopic examination of the fine powder of me- 

 tallic copper, which was obtained by reduction with phosphoric 

 or sulphuric acid from the solution of a salt of copper, afforded 

 decided evidence on the point. Such copper-powder, examined 

 under a magnifying power of 50 or 80 times, presents precisely 

 the same appearance as the spangles in the avanturine ; it 

 consists entirely of brilliant octahedral crystals which exhibit 

 sometimes three-sided and sometimes six-sided faces. Hence 

 it cannot be doubted, that the crystals in avanturine-glass 

 consist of metallic copper, which has been separated from the 

 melted glass containing oxide of copper, by means of the ad- 

 dition of some reducing substance. There are two other cir- 

 cumstances in favour of this view : first, that this glass is so 

 easily fusible that it becomes liquid much under the fusing point 

 of copper ; and, secondly, that Hausmann possesses a copper 

 slag from Biber in Hesse, which includes octahedral spangles, 

 precisely similar to those of avanturine.* 



* GottiBg. Gelehrt. Anzeig., No. 179 and 180; and Poggendorflf's Annalen, 

 1843, No. 2, p. 286. 



