METALS. 



511 



tie sodio boratc and potassic nitrate, in the very 

 smallest-sized Hessian crucible, either with the foot 

 blow-pipe or in a charcoal-furnace, by which means a 

 round, clean button of gold, suitable for weighing, 

 will be obtained. 



This method which I have subjected to a most 

 thorough trial, my experiments having been made 

 almost daily for three and a half months has its 

 disadvantages and its counterbalancing merits. On 

 the one hand, it must be admitted to be tedious, 

 laborious, and, to a considerable degree, uncertain. 

 Some analysts fail with it altogether, while none who 

 have tried it, so far as I know, get closely-agreeing 

 results. 



But, on the other side, it is certain that this 

 method will indicate the presence of gold, and will 

 bring out the gold in a weighable form from pyritic 

 ores, where the assay by smelting will not show a 

 remote trace of the precious metal ; and that where 

 the fire assay shows a certain percentage this will 

 invariably bring out a larger amount. I have ob- 

 tained large returns by this amalgamation method 

 from iron pyritic ores, which have been repeatedly 

 assayed in the ordinary way by chemists of great 

 eminence, with uniformly negative results. 



Fusion of Metallic Arsenic. Mr. J. "W. Mal- 

 lett fuses metallic arsenic by placing the crude 

 metal, in the form of small fragments and 

 coarse powder, in a thick barometer tube of 

 soft glass and small bore, well sealed at both 

 ends, and enclosed in a piece of wrought-iron 

 gas-tube, closed at each end by an iron screw- 

 cap. The space between the tubes is filled 

 with sand, well shaken down, and the whole 

 heated to redness by a charcoal-fire. Arsenic 

 thus treated was found, on cooling, to have 

 fused into a perfectly compact crystalline mass, 

 moulded to the shape of the tube, of steel-gray 

 color and brilliant lustre, of sp. gr. = 5.709 at 

 19 0. It possessed a considerable degree of co- 

 hesive strength as compared with common sub- 

 limed arsenic, and even seemed to exhibit faint 

 traces of flattening before crushing under the 

 hammer. It gradually tarnished on exposure to 

 the air, and presented all the chemical prop- 

 erties of ordinary crystalline arsenic obtained 

 by sublimation. The temperature required for 

 fusion lies between the melting-points of anti- 

 mony and silver. The glass tube used was 

 found greatly distended by the tension of the 

 vapor; and the sand was cemented into a 

 kind of artificial sandstone. 



Filiform Silver. Wherever native silver 

 occurs, it is sometimes found in the form of 

 metallic threads, or wires twisted in every 

 direction, and often bent at sharp angles. Dr. 

 J. H. Gladstone describes, in the London Chemi- 

 cal News, specimens of this filiform silver from 

 Konigsberg, in Norway, associated with calc- 

 spar, and others from Chili associated with 

 greenstone, and in both cases the metal was 

 tough and non-crystalline. Precisely similar 

 threads of silver were produced under the 

 microscope, by decomposing a solution of ni- 

 trate of silver with suboxide of copper. The 

 white filaments shoot forth in every direction, 

 and twist about or double back in their course ; 

 while the cuprous oxide becomes black, split- 

 ting up, in fact, into cupric oxide and cupric 

 nitrate. Most of these threads are so fine that 



their diameter is only ^WFffth of an inch, and 

 a gramme of such silver wire would stretch 

 from London to Brighton, and many are much 

 finer still. Sometimes these filaments will end 

 in crystalline knobs, or crystals of silver will 

 form upon them, as is not unfrequently the 

 case in mineralogical specimens. Attempts to 

 prepare them by means of other substances 

 than suboxide of copper had not proved suc- 

 cessful ; but, -as that substance is by no means 

 a rare mineral, it was thought that their for- 

 mation might result generally from its action 

 on silver salts in solution. 



The Copper Process at Agordo. The copper- 

 ore at Agordo is obtained from an h-regular 

 deposit of iron pyrites lying in black, argilla- 

 ceous schist. The present production of the 

 mines is about 20,000 tons a year, at which 

 rate, it is estimated that it will hold out 150 

 years. About one-third of the ore is worth- 

 less, and the rest carries from two to four per 

 cent, of copper. Mr. John E. Church gives 

 an account of the mode of treatment in the 

 Mechanics' 1 Magazine : " The ore is roasted in 

 heaps containing 250 to 300 tons, the temper- 

 ature being kept very low, and after six to 

 nine months, when the pile was opened, a ker- 

 nel of uuroasted ore was found in each lump. 

 In this kernel is concentrated most of the cop- 

 per which in the beginning had been distributed 

 throughout the lump. A transmission of solid 

 matter so remarkable as this, illustrating the 

 operations by which metallic matter may be 

 concentrated in veins by mundane fires, could 

 not fail to attract attention, and nearly all 

 writers on the metallurgy of copper, and pro- 

 cesses of roasting, have discussed it. These 

 kernels were broken from the surrounding 

 ' shells,' and in this way kernels of a working 

 average of 4.8 per cent, copper were obtained 

 from ore containing 2 per cent, and less ; while 

 the shells would contain about 0.7 per cent. The 

 concentration of copper is so perfect that the 

 real kernel often contains 30 per cent., but, in 

 order to make sure that none of the rich kernel 

 shall be lost, a large quantity of shell is left 

 around it, so that the working average is that 

 above given. 



" Sulphur is collected in small depressions, 

 stamped in the top of the pile. Fine sifted ore, 

 from the lixiviation vats, is stamped into semi- 

 circular basins, and a small quantity of sulphur, 

 from one-fifth to one-half of one per cent, of 

 the ores' weight, collects in them. This is re- 

 fined in the usual way. It contains arsenic, 

 and is not a very valuable product. In 1865 

 the amount made was 50,532 kilogrammes, or 

 50.5 tons. This is 0.3 per cent, of the ore, or 

 0.6 per cent, of the sulphur in the ore." 



The treatment of the two sorts of concen- 

 trated ore herein mentioned is, lixiviation of 

 the shells with precipitation of the copper by 

 iron, and fusion of the kernels. 



The Presence of Copper in Plants. Copper 

 has been found in the plumage of one or more 

 birds, and is now said to have been discovered 



