354 



METALLURGY. (GOLD, SILVER, AND PLATINUM.) 



factory, one of its results is the illustration it 

 affords of the fact that steel possesses a complex 

 structure that can be studied with the micro- 

 scope; that this structure varies greatly with the 

 mechanical and thermal treatment to which it has 

 been subjected ; and that the durability of the rail 

 depends on its structure. It was found from the 

 mechanical tests that rails generally break near 

 their ends, " owing to greater straining action due 

 to discontinuity at the joint," and that the fish 

 joints are an unavoidable source of danger. 



The limonites, or " brown iron ores,'' which are 

 used almost entirely in Virginia, and to a large 

 extent in Tennessee and Alabama, are found prin- 

 cipally in the valley along the Appalachian moun- 

 tains extending from Canada to middle Alabama. 

 The deposits, while they can not be called seams, 

 are generally found along certain definite lines, 

 the ore occurring in lenticular masses, sometimes 

 overlying and sometimes alone, but always in- 

 closed in clay. On account of its intimate asso- 

 ciation with clay, this ore universally requires 

 washing to fit it for the furnace. The irregularity 

 of the size in which it occurs (from the size of 

 a pinhead to bowlders weighing several tons), the 

 richness of the material, and the sand rock or 

 " white horse " encountered are mentioned by Mr. 

 J. C. Foster as some of the uncertainties to be 

 contended with in working the ore. The percent- 

 age of iron varies widely in different localities 

 from an average of not more than 45 per cent, in 

 Pennsylvania and Virginia to an average of 50 per 

 cent, in the furnace at Sheffield, north Alabama, 

 and adjacent parts of Tennessee; and within this 

 monthly or yearly average it ranges greatly from 

 day to day. 



Among the conditions enumerated in an article 

 in the Chemiker Zeitung as indispensable for a pro- 

 tective coating for iron ships that shall meet the 

 requirements of service are that the composition 

 should protect the ship s hull from corrosion ; that 

 it should form a smooth surface, so as to decrease 

 the friction; and that it should dry quickly, so 

 that the cleansing of the submarine parts of the 

 hull and the application of a double coating can 

 be done in a single day. In new steel vessels the 

 black scale on the plates must be removed before 

 applying the coating. Preference is given among 

 the paint compositions which have been used for 

 this work to that proposed by Rahtjen, which 

 consists of a solution of shellac in spirit as the 

 vehicle, with iron oxide and a small proportion 

 of linseed oil, for the first or insulating coating, 

 and the same materials with the addition of ar- 

 senic and quicksilver for the second coat. These 

 compositions are highly commended for their per- 

 manency for the shellac vehicle is but little acted 

 upon by the salt of the sea water. The attach- 

 ment of marine growths to the hull is prevented 

 by the slow action of the sea water on the mercury 

 of the second coating, causing the formation of the 

 poisonous mercuric chloride. These paints have 

 the further advantage of drying quickly. Their 

 defects arise from the smallness of the quantity 

 of mercury that can be incorporated and the grad- 

 ual decrease of their effectiveness through the 

 slight solubility of the shellac. Copper and mer- 

 cury have been found the best mineral poisons 

 to incorporate with the paints. 



The most severe tests of the durability of pre- 

 servative paints for iron work, as described by 

 Mr. Harry Smith before the Newcastle section of 

 the Society of Chemical Industry, consists of 

 painting shallow dishes with the 'pigment and 

 filling them with water, which is allowed to evap- 

 orate slowly. The red lead paints came best out 

 of this trial, being practically unaffected. The 



zinc whites and white leads came next. All the 

 other paints suffered badly, boiled oil the worst. 

 \Vhen painted iron slips were merely exposed to 

 the weather, and when the slips were constantly 

 immersed in water, the results were similar. Good 

 iron oxide was not far behind the lead and zinc 

 paints. Iron oxide makes a tougher paint than 

 red lead, and is, further, more convenient to use. 

 Zinc white is preferable to white lead. The Forth 

 Bridge ironwork is cleaned and painted outside 

 at intervals of three years with a mixture of red 

 lead and iron oxide paint, followed by a finishing 

 coat of brown oxide paint. Where the salt water 

 sprays the ironwork, this is scraped and painted 

 once a year. 



Gold, Silver, and Platinum. Speaking in 

 the Institute of Mining and Metallurgy on the 

 readiness with which a little grease affects the 

 conditions of gold washing, W. S. Welton remarked 

 that the mere touch of a speck of gold with the 

 finger will cause the gold or sand to rise to the 

 surface of water, where it continues to flow. The 

 effect is apparently brought about by a minute 

 portion of grease from the fingers becoming at- 

 tached to the particles. The disastrous effects 

 which may be produced in amalgamation of gold 

 or silver by a minute particle of oil, petroleum, 

 or resin in the water are remarkable. These sub- 

 stances appear to be specially attracted by gold 

 and mercury, and for this reason, at hydraulic 

 mines, it has been found necessary to prohibit 

 washing clothes, dishes, etc., in ditches and 

 streams, and dumping into ditches and sluices. 

 Mercury contaminated with grease or resin be- 

 comes sluggish in running. Comparatively hirgr 

 grains of gold will float upon its surface without 

 becoming amalgamated. The brightness of the 

 metal is changed to a dull lead color, and it will 

 " flour " easily. Distillation will not purify mer- 

 cury from grease or resin, for that goes over too. 

 The author has found great benefit from washing 

 mercury in a strong solution of potash obtained 

 by leaching wood ashes. Flouring and " sicken- 

 ing " are thus overcome, and the yield of gold i> 

 much increased. 



In the process of J. Diether and M. Merz for 

 winning gold from refractory ores the ores are 

 mixed with alkali sulphide and sulphur, or with 

 substances that yield those products when heated, 

 and the mixture is raised to a red heat, which i> 

 kept up for a short time. It is then leached out 

 with water, sulphur being added if necessary. Tin- 

 gold is precipitated together with a gelatinous 

 mass of colloid material or in a pulverulent condi 

 tion, and may be separated by means of a filter 

 press or otherwise. 



Telluride or other ores in which the gold is 

 or appears to be combined with such an element 

 as tellurium, antimony, or arsenic are treated in 

 a patented process at the Golden Link Consol- 

 idated gold mines in closed vessels with a suffi- 

 cient quantity of a weak solution of a polysulphii! 

 of an alkali or alkaline earth metal, to dissolve 

 the tellurium and other bodies without extracting 

 any gold. When heated to from 100 to 200 3 

 C. in the closed vessel, and thus exposed to t.ie 

 combined action of heat and pressure for from 

 one to two hours, the action should be complete, 

 especially if agitation is resorted to. The solution 

 contains the tellurium, which may be recovered 

 from it, and should have extracted no appreciable 

 amount of gold. The residue containing the whole 

 of the precious metal may, after washing, l>e 

 treated with a cyanide solution or otherwise. 



In May's gold extraction process, the ore after 

 bring crushed is exposed to the action of a solu- 

 tion of caustic alkali or alkaline carbonate con- 



