42 



ISOMORPHISM AND THERMAL PROPERTIES OF FELDSPARS. 



character of the phenomenon is noticeable. Its poor conductivity for 

 heat and its viscosity, which, though small compared with the other 

 feldspars, are very great compared with silver, have rounded off the 

 corners until a really constant temperature for a period of a minute or 

 more during the melting is nowhere to be found. The nearest ap- 



Time - I division = 5 minutes 

 Fig. 9. Melting point curves of various feldspars compared with silver. 



proach to a melting point is where the rise in temperature is slowest, 

 and this will occur when the portion nearest to the thermo-element 

 (see fig. 3) melts. 



A series of melting-point curves containing a typical one for each of 

 the observed feldspars is reproduced on page 43 exactly as observed : 



