1915-] HEYL— PLATINUM IN NORTH CAROLINA. 27 



Roanoke river at Weldon, N. C. ; and in the creek bed on the prop- 

 erty at Ruffin. The richest sample (and the only one yielding 

 enough platinum to weigh) was from the mouth of Hogan's creek. 

 It contained about forty-five cents' worth of Pt per ton of gravel. 

 Another sample taken only a few yards away was blank. This was 

 the uniform experience wherever Pt was found, pointing to the 

 occurrence of the metal in sparsely scattered single particles. In all 

 other cases where Pt was found it was merely as an iodide reaction. 



Traces of gold were found at the mouth of Hogan's creek and 

 in the Dan river near Clarksville, Va. 



But I take it it is of less interest to the present gathering to learn 

 that the platinum deposit of North Carolina is commercially unim- 

 portant than to learn something about the nature of the rock that 

 carries the Pt, and the form in which the metal occurs. 



As you see by the samples the rock is evidently sedimentary in 

 its origin. It has a density of 3.03. On roasting it becomes so 

 friable that it may readily be reduced to its grains by the fingers. 

 An analysis of the principal constituents of the rock, made at the 

 Massachusetts Institute of Technology, gave the following figures: 



SiO- 50.01 



CaO 9.02 



MgO 4.83 



AI2O3 15.21 



Fe g.66 



TiO. 2.45 



The rock also contains the alkalies and varying amounts of sulphur. 

 It is noteworthy that it appears to contain no chromium. The sul- 

 phur is present as sulphides of iron, in two forms, soluble and insol- 

 uble in hydrochloric acid, probably the ordinary pyrrhotite and 

 pyrite. It was Dr. Colby's idea that the sulphides carried the plati- 

 num. Our experience negatives that. The samples richest in Pt 

 were often poor in sulphides. Occasionally large crystals of sul- 

 phides would be found, and an assay of the hand-picked sulphides 

 showed no platinum. 



In order to determine, if possible, the form in which the platinum 

 occurred in the rock about 150 assay tons of rock were coarsely 



