JAN. 4, 1921 WASHINGTON: NOTE ON CRUCIBLES 9 



ANALYTICAL CHEMISTRY.— A^o/^' on crucibles used in rock 

 analysis.'^ Henry S. Washington, Geophysical Lab- 

 oratory, Carnegie Institution of Washington. 



It may be of interest to those who are engaged in the analysis 

 of silicates or silicate rocks to put on record my experience with 

 a palau and an iridium-platinum crucible, which have been used 

 for the fusion of rock powders with sodium carbonate. Palau 

 is an alloy, introduced a few years ago as a substitute for plati- 

 num, and is composed of 80 per cent gold and 20 per cent palla- 

 dium. A small percentage of iridium is often alloyed with 

 platinum to impart greater stiffness, as pure platinum is notice- 

 ably soft.- 



It is well known to those analyzing rocks that, when platinum 

 or iridium-platinum crucibles are used for the sodium carbonate 

 fusion, the cold cake sometimes adheres obstinately to the 

 crucible walls, after slight soaking with water in the crucible and 

 gentle heating over a low flame, instead of freeing itself as it 

 "should do." This behavior necessitates prolonged digestion 

 of the adherent melt so as to dissolve the cake, which sometimes 

 results in loss of substance, and alwavs in loss of time. 



This unfortunate behavior is caused, in many cases, by in- 

 dentations or other irregularities in the crucible wall or bottom, 

 brought about by careless handling, such as squeezing the cru- 

 cible to loosen the cake. It is also apparently rendered more 

 liable to happen through the ogee-like curve assumed by the 

 lower parts of the sides of platinum crucibles after long usage; 

 and is easily brought about by attempting to remove the cake 

 before it is quite cold and before it has separated or has started 

 to separate from the walls. The roughness of the inner surface 

 of platinum crucibles is also a determining factor. Even if the 



' Received November 15, 1920. 



- For some studies on the quality and properties of various platinum wares on 

 heating see: R. W. Hall, Journ. Amer. Chem. vSoc. 22: 494. 1900; HulETT and 

 Berger, Journ. Amer. Chem. Soc. 26: 1512. 1904; HillEbrand, Walker, and 

 Allen, Journ. Ind. Eng. Chem. 3: 686. 1911; Burgess and vSale, Journ. Ind. 

 Eng. Chem. 6: 4.52. 1914; 7: 561. 1916; Bull. Bur. Standards 12: 289. 1915 

 (Sci. Paper 254;; Burgess and Waltenberg, Bull. Bur. Standards 13: 365. 1916 

 (Sci. Paper 280); Hillebraxd, U. S. Geol. Survey Bull. 700: 102 (Note 3). 1919., 



