METALLURGY. (SILVEB.) 



475 



zilian Government, made by the late Prof. 

 Hartt, who visited Sao Goncalo in 1875. 



Prof. Orville A. Derby has described a spe- 

 cimen of gold on limonite in the National Mu- 

 seum at Kio Janeiro, from the province of 

 Minas-Geraes, Brazil, which has the appear- 

 ance of having been deposited from solution. 

 The gold-bearing rock is a white-vein quartz 

 resting on a country rock of very quartzose 

 micaceous schist, the exposed side of which 

 had become lined with a crust of black botry- 

 oidal limonite less than a millimetre in thick- 

 ness. The greater portion of the polished 

 surface of this crust is covered with a thin, var- 

 nish-like film of an iridiscent, bronzy color. A 

 third crust or film of reddish-brown earthy li- 

 monite forms a V-shaped streak on one side of 

 the specimen. On various parts of the stone, 

 and all along the V-shaped streak, are minute 

 detached films of gold which adapt themselves 

 perfectly to all the irregularities of the limon- 

 ite, and are shown under the microscope to be 

 uniform or not composed of distinct grains 

 joined together, and to present a surface like 

 frosted metal-work. Films having a similar 

 adaptation to the character of the surface were 

 obtained by allowing a drop of mercurial oint- 

 ment to dry on the specimen. We have in this 

 specimen, therefore, gold resting on the sur- 

 face of a secondary mineral (limonite), and in 

 such conditions that it may be compared to 

 films of limonite deposited from an aqueous 

 solution, or of mercury from suspension in 

 fatty matter. 



Gold has been found on Olancey creek, Jef- 

 ferson county, Missouri, crystallized in the 

 form of a solid octahedral nucleus, to which 

 is added a long divergent brush-like or pris- 

 matic development of the metal on one side or 

 angle, so as to give the whole, according to 

 the description by Mr. W. P. Blake, the ap- 

 pearance of the drawings usually made to rep- 

 resent comets. The total length of these crys- 

 tals is not more than an eighth of an inch. 

 The divergent prisms are very brittle, appear- 

 ing to cleave in planes at right angles to their 

 length. They taper gradually and uniformly 

 to a sharp point and are sometimes composite, 

 or for a part of their length formed of two or 

 more prisms joined side to side. 



Mr. Blake has also from Sonora, Tuolumne 

 county, California, some very small, brilliant 

 crystals of gold, which are seen under the 

 microscope to be hexagonal prisms with smooth 

 and lustrous planes terminated at one or both 

 ends with a pyramid. They resemble the pris- 

 matic gold crystals described by Prof. A. H. 

 Chester as obtained artificially by digesting gold 

 amalgam in nitric acid. 



Dr. James C. Booth, of the United States 

 Mint, has successfully employed for the tough- 

 ening of gold and silver the process of heating 

 them in the melting-crucible till the impurities 

 causing them to be brittle are removed by 

 oxidation, volatilization, or fluxion. The whole 

 amount of gold and silver was recovered, with 



hardly an appreciable loss. Dr. Booth re- 

 marks on the minute proportion of foreign 

 matter, which is capable of imparting brittle- 

 ness, it being less than one part in 75,000 of 

 standard goTd possibly only ^^mr of the 

 whole quantity. 



Silver. Silver exists in masses where it is 

 mined as an ore and as the chief object of ex- 

 ploitation at Silver islet, Lake Superior, and 

 Batopilas in southwestern Chihuahua, on this 

 continent, and in the district of Kongsberg in 

 Norway. The Kongsberg mines have been 

 worked since 1624; those at Silver islet, only 

 since 1868. A description of the mines at 

 Batopilas, and themethods of working them, has 

 been given by Mr. T. H. Leggett, in the " School 

 of Mines Quarterly," from which we derive the 

 following facts : 



The gangue consists of calcite and vein rock, 

 the latter being a more or less metamorphosed 

 condition of the wall-rock, which is usually a 

 greenstone. In some of the mines the silver 

 is found very pure, while in others it is asso- 

 ciated with sulphurets of silver and base met- 

 als. It is itself discolored and apparently con- 

 tains appreciable amounts of arsenic, which 

 give forth the characteristic odor when masses 

 too large to go into the batteries are being 

 broken up under the sledge. The deepest mine 

 is not more than 800 or 900 feet from the sur- 

 face. The entire district is opened up exclu- 

 sively by tunnels, which are so directed as to 

 avoid, by going beneath or away from them, 

 the old Mexican workings at the surface. The 

 veins average from four to six feet in thickness. 

 The oresproduced are classified as follows : First 

 class, in which native silver is plainly visible 

 often in massive form, associated at times with 

 rich silver sulphurets, and assaying from 500 

 to 10,000 ounces of silver per ton. Despuntes 

 is a grade that arises from the hand-clean- 

 ing of the first-class ore, and is intermediate 

 between that and the second class. 



The second-class ore assays from 40 to 300 

 ounces per ton, and may or may not show na- 

 tive silver in small specks or flakes. 



The third-class ore is a stamp-rock, consist- 

 ing of galena and zinc blende, distributed 

 through spar and vein rock, and minute parti- 

 cles of silver visible only on the vanner belt. 

 It assays between 12 and 25 ounces per ton. 

 " Tierras," or soft-vein filling, or gouge, in the 

 regions adjacent to a bonanza, also often form 

 a third-class ore. 



A lot of 3,694| pounds of first-class ore from 

 the Roncesvalles mine, taking 6J hours in run- 

 ning through the batteries, produced 61 pounds 

 of "cabazuelas" or massive silver, weighing 

 from an ounce to several pounds ; 373 pounds 

 of sieved-battery cleanings, assaying 19,274 

 ounces of silver to the ton; and 3.260 pounds 

 of slimes, assaying 659 ounces of silver per ton. 



In running through the batteries, the salt 

 was charged with the ore ; steam was turned 

 on at various times as the pulp thickened and 

 cooled ; and the mercury was added at inter- 



