292 Dr Wollner on the forms of Salts, $c. 



of proto-sulphate of iron. I found also the sulphate of nickel 

 in rliomboidal prisms, and mprisins with a square base,h\it these 

 crystals turned out by Dr Fyfe^ analysis to be a new triple 

 salt, viz. a sulphate of nickel and copper. 



These cases, with several others which might be mentioned, 

 seemed to show that, in all cases where a change of crystalline 

 system took place, there was a change in chemical composi- 

 tion. This opinion, however, is discountenanced by M. Woll- 

 ner's result, and also by Professor Mitscherlich's experiments 

 on sulphur, in which he washable to procure prismatic crys- 

 tals by allowing masses of sulphur of fifty pounds weight 

 to cool slowly after being melted in an earthen-ware pot, 

 while he obtained hemi-prismatic crystals like those of native 

 sulphur, by dissolving sulphur in the carburet, chloruret, and 

 phosphuret of sulphur. 



If it shall be found strictly true that the same substance 

 can crystallize in two different forms belonging to different 

 systems of crystallization, while under each form it consists of 

 the same ingredients combined in the same proportion, there 

 arises a puzzle of no ordinary kind in mineralogy. Many ac- 

 cordant analyses, however, obtained by the first chemists, will 

 be necessary to establish such a result, and, after all, the mi- 

 neralogist may pause and consider whether he will believe a 

 doctrine contrary to many general principles, or suppose that 

 some volatile ingredient may have escaped the penetration of 

 the chemist. 



Since this notice was drawn up, Mr Haidinger has inform- 

 ed us that he has seen in the hands of Dr Gustavus Rose of 

 Berlin, some of the octohedral crystals of sulphate of iron ob- 

 tained by Mr Wollner. The crystals, he assures us, are not 

 regular octohedrons, but irregular octohedrons, which are mere 

 modifications of the common secondary forms of that salt. 

 There is, therefore, in this case, no change in the system of cry- 

 stallization, but merely a change of secondary form. 



