kanolt: melting points of refractory oxides 315 



is established by numerous nearly simultaneous measurements at 

 Mount Wilson, California, and Bassour, Algeria. 



4. Indications of two wholly independent kinds incline us to 

 think that these variations of solar radiation are caused within 

 the sun, and not by interposing meteoric or other matter. 



PHYSICS. — The melting -points of some refractory oxides. C. W. 

 Kanolt, Bureau of Standards. To appear in the Bulletin 

 of the Bureau of Standards. 



Altho a considerable number of oxides are used as refractory 

 materials, the melting points of but few of them have been deter- 

 mined, and many of the determinations that have been made are 

 quite uncertain. For example, some of the determinations would 

 indicate that lime and magnesia are more fusible than alumina, 

 which can easily be demonstrated to be untrue, for alumina is 

 readily fused in the oxyhydrogen flame, while pure lime and pure 

 magnesia are infusible in it, at least under ordinary conditions. 



The principal difficulties encountered in the accurate determi- 

 nation of the melting points are the production of very high 

 temperatures uniform thru a sufficient space and controllable; 

 the supporting of the oxide in the furnace without its contamina- 

 tion by the material used as a support; the avoidance of smoke, 

 which would interfere with the measurement of temperature by 

 an optical pyrometer; and, finally, the accurate measurement of 

 temperature. 



The furnace used was an Arsem graphite resistance furnace, 

 with some minor modifications. This furnace was designed to be 

 used with a vacuum, which prevents the oxidation of the graphite 

 and diminishes the heat losses. It was found impossible, however, 

 to melt lime or magnesia in a vacuum, for they are completely 

 vaporized before the melting point is reached. When these oxides 

 were melted, and also in some other cases, the furnace was filled 

 with a non-oxidizing gas, such as hydrogen, under atmospheric 

 pressure. 



The temperatures were determined by means of a Morse optical 

 pyrometer of the Holborn-Kurlbaum type, which was sighted ver- 



