JAN. 4, 1921 WASHINGTON: NOTE ON CRUCIBLES 11 



num or iridium -platinum on strong ignition. It is to be noted, 

 by the way, that for my fusions the blast was never used. The 

 heating was done for the most part over a half-high Bunsen 

 burner flame, which is quite sufficient to fuse the carbonate mix- 

 ture, and was usually supplemented by a Meker burner during 

 the last fifteen minutes or so. The time of heating varied from 

 forty-five minutes to one hour. About i gram of rock powder 

 and 5 grams of sodium carbonate were used for each fusion. 



The cause of this freedom from adhesion of the cake to the 

 palau crucible walls is uncertain. I am inclined to attribute it 

 chiefly, if not wholly, to the superior hardness and stiffness of 

 the alloy, and especially to its superior polish. The iridium- 

 platinum alloy is almost, but not quite, equal to palau in these 

 respects, while pure platinum is much softer and susceptible of 

 less polish. Whatever the cause may be, and whether the same 

 behavior is true of palau crucibles in general, the observations 

 mentioned indicate that palau is superior to iridium-platinum, 

 and still more to pure platinum, for the purpose of the sodium 

 carbonate fusion in rock analysis. 



I have not tested the resistance of the palau crucible to fusion 

 with potassium (or sodium) pyrosulfate, though some of the refer- 

 ences given above indicate that it loses more weight during the 

 operation than platinum or iridium-platinum. 



It may, however, be of interest to give the data as to loss in 

 weight of the palau crucible, as well as of an iridium-platinum 

 crucible, during some rather long series of fusions of rock powder 

 with sodium carbonate. It must be premised that both crucibles 

 were reserved for this operation, though occasionally they were 

 used for the evaporation of the solution of alkali chlorides in the 

 determination of potash and soda; this, however, w^ould not 

 noticeably affect their weights. 



Since June 12, 191 8 (when it was used for the first time), 

 the palau crucible has been used 47 times for a sodium carbonate 

 fusion. vSince that date the crucible has not been scrubbed with 

 sand, nor was it used for the pyrosulfate fusion or other ignition 

 that might presumably affect its weight. The evaporations for 

 alkali chlorides for which it w^as used were made at 100°, and 



