Kuhlmann on Crystallizations. 43 



KUHLMANN ON CRYSTALLIZATIONS. 



The principal facts and statements contained in M. Fred. 

 Kuhlmann's paper recently read before the Academy of 

 Sciences, are as follows : The author commences by observing 

 that at the moment of the formation of certain bodies, through 

 the agency of chemical action, they are particularly disposed 

 to assume a crystalline structure, and especially so when their 

 origin has been due to a current of gas. Oxydes of anti- 

 mony give beautiful needles when acted upon by sulphide of 

 hydrogen at a high temperature, and oligist iron, under the 

 same circumstances, affords a sulphide of iron having the 

 natural lustre and aspect. Even oxyde of zinc can be trans- 

 formed at a sufficient temperature into a white sulphide, crys- 

 tallized in broad shining plates. Chloride and carbonate of 

 thallium, under the influence of a sulphide of hydrogen cur- 

 rent, yielded at first pseudo-morphic crystals, which, on being 

 sublimed at a higher temperature, afforded the true forms. 



Substituting fluoric acid gas for sulphide and chloride of 

 hydrogen, he obtained fluorides of several metals; but he did 

 not get the fluoride of iron in a crystalline state. Generally 

 speaking, when crystalline minerals are formed by the reaction 

 of gases, their forms are pseudo-morphic; but at higher 

 temperatures many of the crystals modify their form, and 

 this modification, observes M. Kuhlmann, " proceeds from a 

 natural attractive force which gives to the bodies new forms 

 similar to those which they have in nature." 



In studying the crystallization of pastes composed of amor- 

 phous silicon, M. Kuhlmann met with numerous instances 

 in which the molecules of bodies already solidified^ had a 

 tendency to further movements and the assumption of the 

 crystalline form. The presence of water, heat, or mere vibra- 

 tions facilitated this change. 



The tendency of molecules of the same nature to combine 

 when their mobility is augmented by solution or liquefaction, 

 he considers to explain the magnificent crystals of sulphate of 

 lime that often occur in plastic clays, or of different silicates 

 in glass kept for some time in a state of fusion; but when 

 minute crystals imbibe water, and transform themselves into 

 large crystals of great hardness, he thinks it necessary to 

 ascribe to the solid particles a tendency to approach each 

 other in certain directions. He found this phenomenon 

 strikingly exhibited in the deposits of sulphate of barytes 

 near Philippville, in Belgium, and in carbonate of lime in the 

 grotto of Adelsberg in Illyria. In the latter case, the micros- 

 copic crystals impregnated with water formed, in the first 



