CusACK — On the Melting Points of Miner ah. 407 



their behaviour on the meldometer, except Adularia, which bubbles 



Tip. 



The Tourmalines are the most erratic minerals observed, as will be 

 seen from the temperatures given in the tables, ranging as they do 

 over an extent of 90°, a specimen of dark green tourmaline which was 

 quite transparent, having a melting point as high as 1102° C, while 

 one specimen of Schorl from the Wicklow granite melted as low as 

 1012°, and another at 1018°, a specimen of E,ubbellite melted at a 

 temperature nearly intermediate between these, at 1068°; but when 

 the great variety in composition of the tourmaline is considered, the 

 variation in their melting points is not surprising. 



The Oxides present no peculiarity as far as their melting points 

 are concerned ; some are quite infusible, or rather infusible below the 

 fusing point of platinum. Entile melts at 1560° C, or 60° above the 

 melting point of the jDaladium, and the melting of Brookite is not 

 distinguishable from it. These very high temperatures are very 

 difficult to deal with, as the glare and heat of the ribbon are veiy 

 great, and very trying to the eyes. The fact that Brookite and Entile 

 melt at the same temperature tends to show that the melting points 

 of substances of the same chemical composition are not influenced by 

 the molecular structure or difference of symmetry. Zircon probably 

 melts at about 1760°, as when the platinum fused the Zircon dust was 

 stuck on to the ribbon, and was apparently rounded at the edges as if 

 partially melted. It was not observed to melt under the microscope. 

 The specimen of Uranite was rather earthy, but was the only one 

 obtainable, and perhaps the observation is not very trustworthy. 

 Corundum showed no signs of fusion even at the highest tempera- 

 ture. 



Quart% melts easily, but undergoes a long period of viscosity ; 

 nearly 20° of a margin ought to be allowed on either side of the 

 given melting point ; it was observed to be soft at 1406° C, and only 

 ran freely at 1440°, but was liquid at 1425°, being at this temperature 

 observed to flow like thick glycerine when the temperature was kept 

 constant. When the temperature was very slowly raised it was observed 

 to flow more and more easily till at 1440° it flowed like water. 



The Phosphates are interesting as they vary a great deal in their 

 melting points. "Wavellite being quite infusible, while Yivianite, 

 iron phosphate, is fusible at 1114°. Several attempts were made to 

 obtain the melting point of Turquoise, but with no success. It is 

 certainly infusible at 1500°. A specimen of perfectly transparent 

 Apatite from Switzerland was fusible at 1221°. 



E.T.A. PKOC, SEE. ni., VOI. Til. 2 F 



