189 



The Absorption of Iron by Platinum Crucibles in Clay 



Fusions. 



W. M. Blanchard and RoscoE Theibert — DePauw University. 



A short time ago on making a number of clay analyses, we were 

 surprised at the persistent gain in weight of our platinum crucibles and 

 the repeated appearance of ferric oxide after reheating a crucible that 

 had been used in making a fusion. No note of such phenomena could 

 be found in the standard treatises on analytical chemistry at hand, no 

 mention of the absorption of iron by platinum being mentioned by 

 Fresenius, Treadwell and Hall, Olsen, Morse, or Scott. The only men- 

 tion of such action to be found in the literature available was in a paper 

 by Sosman and Hostetter, Jour. Washington Academy, 5, 293-303, and 

 only a synopsis as given in Chem. Abstracts, 9, 1580, was at hand. In 

 this paper account is given of experiments made on the heating of 

 hematite and magnetite in platinum crucibles at high temperatures, 

 resulting in the absorption of iron and the loss of oxygen. The state- 

 ment is made that it is a generally known fact that platinum crucibles 

 will absorb small quantities of iron when heated to high temperatures 

 with ferric oxide. In this synopsis in Chemical Abstracts no reference 

 is made to any published data. 



If a sample of ordinary clay is mixed with the usual amount of 

 sodium carbonate and the mixture fused in the usual manner, the cru- 

 cible will present the appearance of perfectly clean platinum when the 

 product, on cooling, is removed by the treatment with hydrochloric 

 acid. If this crucible is now heated for several minutes over the blast 

 lamp or No. 3 Meeker burner, the lower third of the inside of the cru- 

 cible will have an appearance varying from that of ordinary ferric 

 oxide to that of certain bronzes. If strong hydrochloric acid is now 

 added and the crucible heated gently, what appears to be a rather 

 strong solution of ferric chloride is obtained. If this is removed, the 

 crucible will have again the appearance of clean platinum, but, in many 

 cases, when heated a second time, more iron will be driven to the sur- 

 face and converted into ferric oxide. In some cases it has been found 



