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XXXI. 



THE MELTING-POINTS OF SOME OF THE RAKER MINERALS. 



By ARNOLD L. FLETCHER, M.A., B.E., 



Research Assistant to the Professor of Geology and Mineralogy in 

 the University of Dublin. 



[Read November 26, 1912. Published February 15, 1913.] 



A MOUE accurate knowledge of the actual fusion-points of minerals is the 

 more necessary when it is remembered that the scale of Von Kobell is not 

 only inaccurately spaced, but out of order.' The effect of judging by this 

 method has been to assign, for example, to Augite, Titanite, and Vesuvianite 

 melting-points in the scale of fusibilities of 3, or about 1320° C, whereas their 

 temperatures of fusion (Ousack'^) corrected are approximately 1240° C, 

 1180° C, and 1080° C. respectively. Again, many minerals regarded as 

 infusible BB fuse in reality in the neighbourhood of 1300° 0., i.e. below 

 Almandite, No. 3 in the scale, which melts at about 1315 °C. Such examples 

 could be multiplied. 



The determination of the melting-points of minerals as one of the 

 uses of the meldometer has been emphasized, and the fusion-points and 

 behaviour under high temperatures of some minerals recorded in the original 

 paper.^ 



The subjective method of the determination of melting-point by direct 

 observation under the microscope of the rounding or flowing of minute 

 particles has been used by other observers,* though usually under somewhat 

 different conditions from those under which the present determinations were 

 made, and the resistance of a platinum wire has also been used as a measure 

 of its temperature.* 



'Joly, Proc. Roy. Irish Acad. 3rd Series, vol. ii, 1891, p. 29, et seq. 

 2 Cusack, Proc. Roy. Irish Acad., 3rd Series, vol. iv, 1897, p. 408. 

 ' Joly, ibid., p. 48. 



* Doelter, Zeit. Elektrochem, vol. xii, 1906, p. 617, et seq. Marius van Ledden Hulsebosch, Zeit. 

 Anal. Chem. 1897, xxxvi, p. 685. Douglas, Quart. Journ. Gaol. Soc, vol. bdii, 1907, p. 145. 

 = Burgess and Holt, Proc. Roy. Soc, vol. Ixxiv, 1904, pp. 285-295. 



gCIENT, PROC. R.D.S., VOL. XIU., NO. XXXI. 3 X 



