TRANSACTIONS OT THE SECTIONS. /O 



minute crystals of the iron-ore, possessing a high metallic lustre. By boiling the 

 sand for a sufficient time in hydrochloric acid, the whole of the iron was removed, 

 and nothing but the perfectly white quartz remained. The specific gravity of the 

 sand was 2'08, and the gi-aius would just pass through a wire gauze, the apertures 

 of which measured the 1(9 ,000th part of a square inch. 



On comparing this with some ironsaud which occurs mixed with the soil in 

 some parts of the country round Vesuvius, the chemical composition was found to 

 be the same, though the grains of the older product were rather smaller, and pre- 

 sented under the microscope an unmistakably water-worn appearance. The spe- 

 cific gravity of these was 467 ; and they were more readily attracted by the magnet, 

 on account of their possessing a larger proportion of iron relatively to the quartz. 



Both samples differ from the magnetic ironsand of New Zealand (most probably 

 ejected from the volcano Mount Egmont) in not containing titanium; neither do 

 they contain by any means so large a proportion of iron oxide as compai'ed with the 

 siliceous nucleus. 



It is probable that the sand which fell during the recent eruption of Vesuvius 

 varies considerably in the relative proportions of iron and silica, and that as the 

 heavier or the lighter substance prevailed would be the distance to which it would 

 be can-ied by the wind from the mouth of the volcano. 



Onjlliform Native Silver. By J. H. Gladstone, Ph.D., F.B.S, 



Native silver occurs either in bunches of crystals or in threads or wires twisted 

 in every direction, and often bent at sharp angles. The fibrous or filiform silver is 

 tough and non-crystalline, though the threads are sometimes incrusted with crystals 

 of the same metal. It occurs in association with a variety of minerals ; for instance 

 with quartz in Cornwall, with pyrites in Saxony, with calc-spar in Norway, and 

 with greenstone in Chili. 



Now both electrolysis and the replacement of silver in solution by a more posi- 

 tive metal give the silver in a crystalline condition, and the crystals often closely 

 resemble those found in nature. But if nitrate of silver dissolved in water is 

 allowed to act upon suboxide of copper, there shoot forth after a little time white 

 filaments, which often run rapidly forwards into the liquid, or twist shai-ply round, 

 or perhaps even double back on their course precisely like the native filiform 

 metal. This under ordinary circumstances is only visible by means of the micro- 

 scope, and most of the threads are so fine that their diameter is oqly about the 

 -^jio^ of an inch, and a gramme of such wire would stretch from London to 

 Brighton. Many are very much finer than this, while others again are much 

 thicker. They never ramify or show the usual signs of crj'stalline structure. 

 Crystalline silver, however, will sometimes be deposited on these filaments, or tliey 

 will terminate in thick crystalline knobs ; and under certain circumstances crystal- 

 line tufts may make their appearance from the commencement. As the silver 

 grows, the yellow or red suboxide of copper becomes black in colour. The reaction 

 might be supposed to be 



2(AgN03)-f-Cu,0 = 2Ag-fCuO+Cu(N03)„- 



and no doubt this decomposition occurs ; but the solid residue was found to con- 

 sist not merely of black oxide of copper and threads of silver, but also of an inso- 

 luble basic nitrate. 



Mineral suboxide of copper was found to give the fibrous metal with silver 

 nitrate, just as the oxide which had been artificially prepared ; but attempts to 

 prepare the metallic threads by means of the chloride of silver in saline solutions 

 were unsuccessful. 



On the mutual heljjfnhiess of Chemical Affinltij, Heat, and Electricity in 

 ivoducinfj the Decomposition of Water. By J. H. Gladstone, F.B.S., and 

 Alfred Tribe, F.CS. 



Some metals are able of themselves to displace the hydrogen of pure water, while 

 other metals are unable. Zinc, if perfectly pure, is just incapable of doing so ; but 



