512 



Mr. H. C. Sorby on Jargonium. 



[June 17, 



as great as that between any other two closely related elements. Judging 

 from Mr. D. Forbes' s analysis, kindly made at my request, and from a 

 comparison of the spectra, the amount of jargonia in different jargons 

 varies up to about 10 per cent. The entire or comparative absence from 

 the zircons of Miask, Fredericksvarn, and various other localities, appears 

 to explain some of the facts which led Svanberg* to conclude that zircons 

 contain more than one earth. He was so far correct, but failed to esta- 

 blish the existence of any substance with special chemical or physical pro- 

 perties ; and if, as is probable, the Norwegian zircons, which, according to 

 his views, contain such a notable quantity of this supposed new earth as 

 to have led him to give it the name noria, were from Fredericksvarn, 

 and if the Siberian were from Miask, his norium cannot be looked upon as 

 equivalent to my jargonium, which is almost or quite absent from those 

 zircons. 



The most remarkable peculiarity of jargonium is that its compounds 

 may exist in no less than three different crystalline states, giving spectra 

 which differ from one another as much as those of any three totally dif- 

 ferent elements which give the most striking and characteristic spectra. 

 Several substances can be obtained in two physical states, giving different 

 spectra : but usually only one of them is crystalline ; the other is the 

 vitreous or colloid condition. Crystalline minerals, coloured by oxide of 

 chromium, do indeed show two types of spectra, but I am not aware 

 that they ever both occur in the same mineral. In the case of jargonium, 

 however, the three types of spectra are all met with in crystalline modi- 

 fications of apparently the same compound. 



The most characteristic test for jargonia is the spectrum of the borax 

 blowpipe beads, seen with the spectrum-microscope, which enables us to de- 

 tect it in zircons containing less than one per cent. As much of the earth or 

 natural silicate as will completely dissolve should be melted in circular loops 

 of platinum wire, about § of an inch in diameter, with a mixture of borax and 

 boric acid, and a very strong heat kept up till crystals begin to be deposited, 

 owing to loss of the solvent by volatilization. On removing the beads 

 from the flame they remain clear, and show a few acicular crystals, but 

 give no absorption-bands in the spectrum. On reheating to a temperature 

 just below very dull redness, they turn white, and so very opaque that no 

 ordinary light will pass through them. When, however, a small and very 

 bright image of the sun is formed in their centre, by means of an almost 

 hemispherical condensing lens of \ inch diameter, and a cap placed over 

 the object-glass, with a round hole less than the beads nearly in the focus, 

 so as to prevent the passage of extraneous light, they are seen to be illu- 

 minated by transmitted light of about the same brilliancy as that of a 

 bright cloud, so as to give an excellent spectrum, without being at all daz- 

 zling. In the case of beads containing jargonia, the spectrum differs com- 

 pletely according to the temperature at which the included crystals have 

 * Pogg. Ann. 1845, vol. Ixv. p. 317. 



