30 HEYL— PLATINUM IN NORTH CAROLINA. [February 7, 



was discovered that it was almost impossible to obtain a blank when 

 the rock was largely ferruginous, while on rocks composed mainly 

 of quartz there was no difficulty in this respect. In no case was 

 anything more than the extremely delicate iodide reaction obtained. 

 In applying this test it is important to note that it is interfered with 

 by the presence of iron, nitric acid, and alcohol. The latter sub- 

 stance is likely to be the most frequent cause of failure to obtain 

 the reaction. In certain ferruginous rocks, when the point was 

 reached where the platinum, if present, should remain insoluble on 

 the watch glass after taking up the sal-ammoniac with 60 per cent, 

 alcohol, there was often an almost microscopic trace of a white 

 residue. Performing the filtration by faith, and washing with 95 

 per cent, alcohol, also by faith, the critical point of the procedure 

 was reached. If the supposed precipitate was now dissolved ofif the 

 filter by hot water, no iodide reaction could be obtained; but if the 

 filter was first dried until all odor of alcohol had disappeared, an 

 iodide reaction could often be obtained. In this way reactions were 

 obtained from certain building stones from Lower Merion township, 

 Montgomery county, Pa., and from a trap dyke in the neighborhood 

 of our laboratory in Westchester county, N. Y. The sands of the 

 Bronx river, a small stream in our vicinity, gave no reaction when 

 unconcentrated, but when concentrated by hand panning a reaction 

 could be obtained. Bearing in mind the relation of platinum to the 

 iron group, and the fact that iron always accompanies platinum, it 

 is not so surprising that platinum' should occur in small traces with 

 iron wherever the latter is found. 



We also examined the rocks near Sassamansville, Berks county. 

 Pa., which are mentioned in Kemp's report as giving irregular indi- 

 cations of Pt, and found iodide traces in several samples. To judge 

 by the depth of color, these samples were not as rich as certain of 

 the Lower Merion building stones. 



Laboratory of the Commercial-Research Co., 

 tuckahoe, n. y. 



