23 AUotropy. 



ALLOTROPY. 



BY W. B. TEGETMEIER. 



The singular phenomena which are known to chemists under 

 the title of AUotropy are so remarkable, and can be so easily 

 illustrated by means of a few simple experiments, capable of 

 being performed without any particular apparatus, that they 

 may advantageously form the subject of one of the series of prac- 

 tical papers that were commenced in a former volume of the 

 Intellectual Observer. 



The term AUotropy is employed to signify the remarkable 

 circumstance, that the same substance can exist in two or more 

 totally different states, which are distinguished from each other 

 by extraordinary variations both in their physical and chemical 

 properties. The same substance, for instance, may be in one 

 state fearfully poisonous, in another perfectly harmless. In 

 one condition it may be brittle, in another extremely elastic. 

 Again, it may have a liquid and several solid states, being in 

 one vitreous or glassy, in another crystalline, and in a third 

 perfectly amorphous. These singular changes of condition are 

 the more remarkable from the fact that any one may be pro- 

 duced at the will of the operator, each particular state being 

 readily convertible into either of the others. 



The most familiar examples of allotropic substances are the 

 elements carbon, phosphorus, and sulphur. Of these the latter 

 is most easily experimented upon, and as some new facts 

 relating to its allotropic conditions have recently come to light, 

 avc will select it for illustrating this peculiar class of phe- 

 nomena. 



Common commercial sulphur, or that found native in seve- 

 ral parts of the earth, is soluble in turpentine in most of the 

 mineral oils, as benzine, and also in bisulphide of carbon; when 

 crystallized, it exists in the form of elongated octohedrons. If 

 a tew pounds "' the common sulphur be melted in a crucible and 

 allow.i I to cool slowly until a crust forms on the surface (when 

 the eras! should be broken and the liquid exterior poured out), 

 Die sides of flic cavity will be found to be lined with transparent 

 yellow i-li needle-like crystals, having a totally distinct form 

 from the octohedral variety, being in long oblique prisms. 

 These crystals spontaneously change in the course of a few days 

 •'mil | mi int> the first-named more opaque octohedral form, 



the i retaining their outward shape, but in reality being 



constructed of an aggregation of minute octohedrons. 



This change from the transparent prismatic to the opaque 

 octohedral form is one of great importance in the plastic arts. 

 Sulphur, when melted at a low temperature, and first cast, pos- 



