234 Damour on the Density and Refractive Index of some Zircons. 



The latter is Vivianite in small crystals quite like those of Com- 

 mentry. It has never before been artificially prepared. 



Phosphate of nickel and soda, 2NiO, NaO, P0 5 -f 14HO 

 Phosphate of cobalt and soda, 3CoO, P0 5 + 2NaO, HO, PO 5 



+ 8HO. 



The latter is in small crystals of a magnificent blue colour. 



M. Damour* has communicated a note on the density of 

 zircon. In the course of his researches on the density of minerals, 

 he had been led to observe the great variations in the density of 

 zircon, which oscillates between 4*04 and 4*67 ; and he set him- 

 self to ascertain whether this arose from a difference in composi- 

 tion, or was due to a special molecular state. He analyzed a 

 specimen from Ceylon, of the specific gravity 4*183, and found 

 that the analytical results corresponded with the formula of zir- 

 con, ZrO 2 SiO 2 . Results very closely agreeing with these were 

 obtained by Berzelius for a zircon of Epailly which had the spe- 

 cific gravity 4*667. 



The difference did not arise therefore from chemical composi- 

 tion. Damour accordingly endeavoured to modify the molecular 

 state. A zircon from Ceylon, whose density was 4*183, was 

 heated to dull redness, without, however, producing any loss of 

 weight or alteration in density. But heated to an incipient 

 white heat its density rose to 4*534, there being little or no loss. 

 The same experiment, repeated five times on different specimens, 

 gave always the same result — an increase of y^ to ^ in the 

 density. 



A temperature of white redness produced by a turpentine 

 flame fed by air is inadequate to melt zircon. By the oxy hydrogen 

 blowpipe, however, the surface becomes fused and covered with 

 a thin layer of white enamel. 



Damour compared the refractive indices of the specimens dif- 

 fering in their density. Senarmont had found for a specimen 

 from Ceylon, whose density was 4*636, the numbers 



For the ordinary ray . co = l'92\ n ■* 

 For the extraordinary ray 6 = 1*97 J* ^ 



And Damour found for another specimen from Ceylon, which 

 had the density 4*210, the numbers 



For the ordinary ray . co = 1*851 £ -, 



t? t-L v i oa r l° r re d rays. 



t or the extraordinary ray e=l*8bj J 



Hence the refractive index increases with the density. 



It is doubtless to the allotropic state of zirconia that these 

 different physical properties of zircon are due. Zirconia, as ob- 



* Comptes Rendus, January 18, 1864. 



