636 The Philippine Journal of Science 1923 



Palladium and gold do not interfere with the test for iridium. 

 Platinum tends to make the red-brown octahedra a lighter shade. 

 Silver and mercury interfere. 



Platinum salts yield highly refractive pale yellow octahedra 

 with hmt. As the platinum solution becomes more dilute the 

 crystals formed when hmt is added become smaller. As the 

 small crystals are almost colorless care must be taken not to con- 

 fuse these with the colorless octahedra formed with hmt and bis- 

 muth or tin compounds. The platinum crystals, however, turn 

 dark reddish brown upon the addition of a tiny fragment of 

 potassium iodide. 



The platinum-hexamethylenetetramine compound 10 has the 

 formula 2(C C H 12 N 4 . HCl)PtCl 4 + 4H 2 0. 



In the presence of iridium the platinum crystals are darkened 

 somewhat, so that they have a color between the yellow of the 

 platinum salt and the red-brown of the iridium salt. 



In mixtures of platinum and palladium, the former usually 

 comes out first, the latter on standing or by scratching. The two 

 are readily distinguished under crossed nicols as the palladium 

 crystals alone exhibit extinction. Large amounts of silver or 

 mercury interfere with the test for platinum. 



Sensitivity with hmt, 1 : 8,000. 



Palladous salts yield with hmt characteristic, very thin, color- 

 less plates strongly polarized under crossed nicols. The crystals 

 tend to grow large if the drop is left undisturbed, but give small, 

 thin crystals if the preparation is scratched (Plate 1, fig. 6) . 

 An excess of hmt is necessary. The crystals form around the 

 melting fragment of hmt. When a tiny fragment of potassium 

 iodide is added the crystals are colored a dark brown. 



Mercury interferes with the test for palladium. See remarks 

 under platinum. 



Sensitivity with hmt, 1 : 1,000. 

 Mercuric salts form with hmt in neutral solution colorless, 

 square-ended, slender prisms belonging to the monoclinic system 

 (see Plate 2, fig. 8) . The crystals often form rosettes of needles. 



ll Tollens, B., Ber. d. deut. Chem. Ges. 17 (1884) 655. 



