54 ISOMORPHISM AND THERMAL PROPERTIES OF FELDSPARS. 



material but with different rates of heating. It will be noticed that 

 the absorption begins to be noticeable at a slightly lower temperature 

 if the heating is slower. 



This peculiar behavior shown by compounds which melt to form 

 hyperviscous liquids seems not to have been observed before and to 

 contain features of more than ordinary interest. Here are evidently 

 crystalline substances which not only can exist for considerable peri- 

 ods of time at temperatures far above their melting temperatures, 

 but which melt with extreme slowness in the lower portion of this 

 range of instability. It would certainly be no exaggeration to say 

 that the albite with which we worked would require some weeks to 

 reach the amorphous state if maintained at a constant temperature 

 of 1125 . 



An interesting question arises here as to the state of the crystalline 

 material at temperatures above its melting point. It is easily con- 

 ceivable that the crystals are merely superheated without loss of any 

 of their properties as solids, and that they thus present an analogy to 

 superheated liquids. In the transformation (Umwandlung) of a solid 

 crystalline substance into another crystal form such superheating has 

 long been known. The change is dependent upon temperature and 

 pressure like ordinary fusion, but it is possible to pass the transforma- 

 tion temperature in either direction. This must be due to the unfa- 

 vorable opportunity for molecular motion which solids afford, and the 

 latter should differ in no essential particular from ultraviscosity. 



On the other hand, it does not seem a violation of any known prin- 

 ciple to conceive cases of unstable equilibrium in which the molecules 

 of a liquid are oriented as in a crystal. Maxwell's demons might 

 arrange them much like a school of fish, and there is no apparent reason 

 why the fluidity should be destroyed thereby. Were such an arrange- 

 ment one of minimum potential, the mass would be a liquid crystal. 

 In the supposed case such a substance would possess a melting point 

 dependent upon the temperature and pressure above which Maxwell's 

 definition* of a true solid that its viscosity be infinite would no 

 longer obtain, although deorientation might not become apparent, in 

 the face of extreme viscosity, for a considerable time afterward. Such 

 a melting point would be determinable only with the greatest diffi- 

 culty, for all the functions mechanical, thermal, or electrical which 

 usually become suddenly discontinuous at the melting point would 

 be equally powerless to define a change of state in the face of such 

 extreme molecular inertia. 



* Maxwell's Scientific Papers, vol. 2, p. 620 



