22 



IV. 



Calculated . 



Found. 



6 ZnO, 

 2 SiO^, 

 CO,, 

 4 HO, 



66-996 

 17 051 

 6-056" 

 9-900. 



15-956 



66-844 

 17-471 

 4-637- 

 10-834 



99-786 



iN'othing can be simpler than the connexion which these formnlse 

 establish between the composition of the different balls. According 

 to them, they are compounds of two bodies, which are already well 

 known, and one of which abounds in the locality, namely, calamine or 

 hydrated silicate of zinc, and a dicarbonate of zinc, which may be precipi- 

 tated by sesquicarbonate of soda, from a solution of sulphate, and 

 which has been obtained by Eoussingault combined with water as 

 2(2ZnO,C02) + 3H0 ; and by Schindler, 2ZnO,C02 + 2H0. The brief 

 description which we have giyen in the first part of this paper of the 

 circumstances under which these minerals occur, is sufficient to show 

 that all the conditions for the formation of such a dicarbonate in the 

 presence of a solution of silicate of zinc coexist. If these formulae be 

 correct, dicarbonate of zinc and disilicate of zinc are isomorphous and 

 these compoands are analogous to those formed by bisulpliate of potash 

 and bichromate of potash, sulphate of potash, and chromate of potash, 

 and the nitrates of potash and silver ; and, consequently, similar com- 

 pounds may be formed in endless proportions. Perhaps some of the 

 zinc ores from Wiesloch, analysed by C. Iliegel,f may belong to this 

 category ; indeed, the affinity of silicate of zinc for carbonate of zinc, 

 appears to be considerable. Almost every specimen of the former con- 

 tains carbonic acid, even the transparent fibrous kinds. 



Filrom HemimorpTiite, or Sydrated Disilicate of Zinc {Calamine). — 

 After discovering the simple relationship of the formulse of the balls con- 

 taining different proportions of water, the idea at once suggested itself 

 to us that the isomorphism of the disilicate and dicarbonate might explain 

 the want of atomic relation of the water, which is almost invariably ob- 

 served in all the specimens of calamine that have hitherto been ana- 

 lysed. In order to test this hypothesis, we analysed a specimen of per- 

 fectly colourless (and in small pieces transparent), fibrous, hydrated si- 

 licate of zinc, which is associated with the hydrocarbonate from Dolores 

 mine. This specimen was found to contain carbonic acid, as will be 

 seen by the following table : — 



* See the paper " On the Action of Heat upon Silicates of Zinc," infra^ for an ac- 

 count of some curious phenomena which appear to corroborate this view in a very re- 

 markable manner. 



t Archiv. d. Pharm. (2) Bd. Iviii., p. 29, quoted by BischofF— Lehrbuch der Che- 

 miachen Geologic 2*6'- Bd. p. 1883. 



