290 Dr Wollner on the different Primitive Forms of Salts 



solution of ordinary copperas, and also from the octohedral 

 sulphate, by sometimes plunging into it a crystal of alum, and 

 sometimes a crystal of sulphate of iron, but he could not suc- 

 ceed. 



He now directed his attention to the nature of the mother 

 waters, in which this sulphate had crystallized, in order that 

 he might find a method of reproducing this solvent at pleasure. 

 The specific gravity of these waters was 1.358, and they were 

 composed as follows : 



Sulphate of magnesia, with traces of gypsum, 6.635 



Sulphate of alumine, - - 6.295 



Sulphate of the protoxide of iron, - 12.000 



Muriate of the protoxide of iron, - 9-975 



Free muriatic acid, - - 0.570 



Water, - - - 64.525 



From this result Dr Wollner was able to reproduce arti- 

 ficially a solution capable of yielding octohedral crystals of 

 sulphate of iron, by dissolving in water the following salts. 



Sulphate of magnesia, - - - 11.5 



Sulphate of alumine, ... 6.3 



Sulphate of iron, - 22.0 



Crystallized muride of iron, - - 18.0 



Muriatic acid, sp. grav. 1.167, - - 2.3 



If we now concentrate this solution to a density of 1.358, 

 and dissolve in a 1000 parts of weight of the liquid 125 

 parts of ordinary copperas, and leave the solution to itself for 

 twelve hours, we shall obtain crystals of the sulphate of iron, 

 having the octohedral form of alum. 



OBSERVATIONS BY THE EDITOR. 



The subject of the preceding observations is one of the most 

 interesting in crystallography. Several facts analogous to 

 those mentioned by Dr Wollner have been long known, but 

 he is the first person who has investigated with care the cir- 

 cumstances of the experiment, and pointed out the method of 

 reproducing the crystals at pleasure. We do not allude to 

 the mere change of crystalline forms, which is produced by 



