21 



M. Terreil also examined one of these siliceous balls ; it had the spe- 

 cific gravity 2-762, and appears to have been analogous to No. lY. in 

 other respects. As he could not remove the carbonate by means of very 

 dilute acetic acid without also decomposing the silicate, he concluded 

 that the two were in chemical combination. The specimen he examined 

 contained 12-92 per cent, of water, of which 5-16 per cent, was driven 

 off between 100° and 200° per cent. ; he accordingly reckons this part as 

 hygroscopic water. Considering silica to be a teroxide, he assumes the 

 formula [ZnO,Si03, (ZnCHO)^]^ + ZnO,C02. This is a very complex 

 formula, in which we have to assume the combination of silicate of 

 zinc with hydrate of zinc, and the combination of this compound with 

 anhydrous carbonate of zinc. We also believe that the carbonate is in 

 combination with the silicate ; but having had a greater variety of spe- 

 cimens to examine, we have, as we believe, arrived at a simpler expres- 

 sion of their composition. The following are the formulae which we 

 propose for the compounds examined by us : — - 



I._ 2 ZnO,Si02 + 3 (2 ZnO, CO^) + 9 HO. 

 II.— 2 ZnO,Si02 + 2 (2 ZnO, CO^) + 8 HO. 

 III.— 2 (2 ZnO,Si02) + 3 (2 ZnO, CO2) + 14 HO. 

 lY 2 (2 ZnO,Si02) + 2 ZnO, CO^ + 4 HO. 



The following table shows the accordance between the theoretical 

 composition calculated from the formulas, and the results found : — 



Calculated. Found. 



8 ZnO, . . 64-598 64-549 



SiO^, . . 6-165 6-493 



3 CO,, . . 13-1261 12-246-1 



9H0, . . 16-109r^^^^ • • 16-672r^^^^ 



99-960 



II. 



, A. ^ 



Calculated. Found. 



6 ZnO, . . 62-365 61-865 



SiO, . . 7-936 8-292 



2 CO,, . . 11-2641 11-301 



8H0, . . 18-433/^^ ''^^ • • • 18-624 



100-082 



III. 



, — 



Calculated. Found. 

 10 ZnO, . . 61-515 . .... 62-266 



2 SiO,, . . 9-393 9-214 



3 CO, . . 10-0001 10-101 W4.0 

 14 HO, . . 19-090r^^^^ • • 19-362r^^^^ 



100-943 



