lirTO.] 4oJ [Gciitll. 



dirt excavated in Philadelphia, holding silicate jems indica- 

 tive of the presence of gold. 



Dr. Gentli stated that, according to Del Rio, an alloy of gold and rho- 

 dium is found in Mexico, which contains from 34 to 43 per cent, of the 

 latter metal. This discovery has never been confirmed, and there is per- 

 haps no mineralogist living who ever has seen it. Some experiments 

 which he has lately made with residues from Sau Domingo gold leave very 

 little doubt as to the existence of this very interesting substance. Prof. 

 Gabb sent a lot of gold from San Domingo to Dr. Horn, from which the 

 latter dissolved the gold by aqua regia, and placed the very minute residue 

 into his hands ! This consisted of scales of Iridosmine, a dull, yellowish 

 substance, in microscopic roimded and angular grains, and a silicate which 

 under the microscope appeared to be topaz. One of the yellowish grains, 

 on being flattened out in an agate mortar, assumed metallic lustre and a 

 pale yellow color. It was almost insoluble in aqua regia, but by treating 

 it for several days with a large excess of this solvent, it was finally brought 

 into solution. A trace of chloride of ammonium was added, and the whole 

 evaporated to dryness and sufficiently heated to reduce the gold. Mixed 

 with this were microscopic reddish crystals, which were dissolved in boil- 

 ing water, filtered, the filtrate evaporated to dryness, and the residue 

 slightly heated, by which it "assumed a reddish brown color. On being 

 fused with bisulphate of potash it gave a slightly rose-colored mass, solu- 

 ble in water, and precipitated yellow by ammonia. From these reactions 

 there seems to be no doubt that the yellowish grains are rhodium-gold. 



Dr. Horn states that the gold received from Prof. Gabb came from the 

 South side of the Island, and contained about 95 per cent, of gold. Dr. 

 Genth remarked that some of the gold from the North side is of a pecu- 

 liar nature; that several years ago a lot had beeir sold in this city and 

 New York to jewellers, who stated that they could not work it, as it con- 

 tained a substance unknown to them. It is very probable that this was 

 also rhodium-gold. 



Dr. Genth communicated the result of panning sand and gravel of the 

 Delaware River, dug from a cellar at 106 Arch street. After removing 

 quartz and other light substances, a considerable quantity of heavy black 

 sand remained, which contained a little magnetite, but a large quantity 

 of titaniferous iron (menaccanite). These were treated and dissolved 

 with chlorhydric and sulphuric acid, which left the silicates clean enough 

 for further examination. These consisted principally of very brilliant 

 but microscoijic zircons, some garnets and a few yellowish green grains 

 of the appearance of chrysolite. The observed mineral generally accom- 

 pany gold, but not a particle of the latter could be found. This negative 

 result, however, does not prove its absence, because the quantity of the 

 sands washed was not large and they did not come from the bed rock, 

 where they are always far richer. 



Prof- Cope exhibited a portion of the dorsal spine of a 



