450 Chronicles of Science. [July, 



9. MINERALOGY. 



Exactly eighty years ago, the German chemist, Klaproth, disco- 

 vered a new earth, or metallic oxide, in a certain mineral found in 

 the sands and gravels of Ceylon, and occasionally cut and polished 

 as a gem. As this mineral had long been known under the name 

 of zircon — a word apparently of Arabic origin — the new earth 

 received the appropriate name of zirconia. The same oxide was 

 likewise found in the brightly-coloured stone known as the hjacinfh 

 — not indeed the hyacinth of the ancients, which appears to have 

 been our sapphire, but the gem so-named by the modern mineral- 

 ogist — and it was then demonstrated that the zircon and hyacinth 

 are virtually the same mineral, both being silicates of zirconia. 

 In 1845, the Swedish chemist, Svanberg, endeavoured to show that 

 in the zircons of Norway and of the Urals the zhconia is accom- 

 panied by another substance which he termed not'ia ; but whether 

 this is really a distinct earth has not been satisfactorily determined. 

 About three years ago. Professor Church was led to examine seve- 

 ral specimens of zircon under the micro-spectroscope ; and observing 

 that some of them exhibited peculiar absorption bands, not given 

 by pure sihcate of zirconia, he conjectured that they might possibly 

 be due to the presence of Svanberg's norium. Utterly ignorant of 

 Professor Church's observations — the results of which were pub- 

 hshed only in the shape of a letter inserted in a popular journal — 

 Mr. H. C. Sorby has for some time past been engaged in the 

 spectroscopic examination of the zircons of Ceylon. AVhen light is 

 transmitted through certain transparent specimens of zircon, and 

 is then analyzed by the eye-piece of his spectrum-microscope, it is 

 seen that the luminous spectrum is traversed by more than a dozen 

 well-defined narrow black lines. As these absorption bands are 

 not given by any other known substance, Mr. Sorby regards them 

 as indicating the presence of a new earth associated with zu'conia ; 

 and as they are exhibited chiefly by those pale-coloured varieties of 

 zircon which are known as jargoon or jargon, he proj^oses to name 

 the new metal jargonium. Professor Church, however, has sug- 

 gested for this supposed element the name of nigrium. It would 

 appear from Mr. Sorby 's further researches that the earth jargonia 

 is capable of existing in two distinct allotropic conditions, having 

 different densities and different optical properties. Comparatively 

 few Cingalese jargons exhibit in their natural state well-marked 

 lines, but by exposing an ordinary specimen for some time to a 

 bright-red heat the altered mineral gives a spectrum which is 

 traversed by a fine series of absorption bands.* 



♦ 'Chemical News,' March 12, April 16 and 30, 18G9 ; also paper printed for 

 private circulation at soiree of the lloyal Society. 



