482 



METALLURGY. 



being dissolved as a chloride and the sulphur set 

 free, when the ore is ready for calcination. 



For certain special economical reasons the 

 higher grade sulphide ore is treated at Broken 

 Hill, New South Wales, by the roast reduction 

 process direct. The ore treated contains from 30 

 to 35 per cent, lead, 18 to 25 per cent, zinc, 10 

 per cent, iron, 10 per cent, gangue, and from 26 

 to 30 ounces of silver per ton. The roasting is 

 carried on at a low temperature, with no attempt 

 to sinter. The roasted ore is smelted with about 

 one fourth its weight of carbonate ore, together 

 with the proper proportion of fluxes and old slag 

 to form a fusible slag and to render the charges 

 permeable by the blast. Slags of various types 

 were produced, some of which contained as much 

 as 20 per cent, of oxide of zinc, and were fusible. 

 Of the various types tried up to the present time 

 that which has given the best results is a basic 

 slag having the following composition : Silica, 

 24 per cent. ; oxides of iron and manganese, 36 

 per cent. ; zinc oxide, 16 per cent. ; lime, 16 per 

 cent. This runs well even if the sulphide of zinc 

 should go a small proportion more than is shown 

 above. It is fairly clean so far as its lead and 

 silver contents are concerned, and it separates 

 from zinciferous matter as well as other types of 

 slag. 



For estimating gold -and silver associated with 

 antimony, Ernest A. Smith mixed 500 grains of 

 the metal crushed to a fine powder with litharge, 

 1.000 grains, potassium nitrate, 200 grains, and 

 sodium carbonate, 200 grains, and heated in a 

 wind furnace at a dull-red heat for about fifteen 

 minutes. When quite tranquil the contents were 

 poured into an ingot mold, and the button of 

 lead, which weighed about 500 grains and was 

 perfectly malleable, was cupeled direct. The 

 resulting gold-and-silver button was parted with 

 dilute nitric acid in the usual way. 



To estimate the gold and silver in metallic 

 bismuth, 500 grains were carefully cupeled, and 

 the buttons of precious metals thus obtained 

 were parted in the usual manner. The bismuth 

 may be extracted from the cupels by rejecting 

 the white portion, and crushing the stained por- 

 tion to a fine powder and fusing at a red heat 

 with fluxes. 



Aluminum. By the Hall process for prepar- 

 ing aluminum the price of that metal has been 

 reduced from $15 per pound to 50 cents per 

 pound, making it, bulk for bulk, as inexpensive 

 as copper and cheaper than nickel or tin. With 

 it, working on a large scale, it is estimated that 

 the cost of making pure aluminum can be 

 brought down to 17 cents per pound. The pro- 

 cess consists in reducing the oxide of aluminum 

 by dissolving it in a fused bath consisting of a 

 fluoride of aluminum together with a fluoride of 

 some other metal more electro-positive than 

 aluminum, and precipitating the metallic alu- 

 minum from this ore by electrolysis. The fused 

 fluoride bath remains practically constant, and 

 therefore costs but little. The 'ore is dumped 

 into it, and, upon dissolving, the metal is imme- 

 diately electrolyzed out by the current at the 

 negative pole, and falls to the bottom of the 

 pots. These are tapped or ladled out without 

 disturbing the operation of the process, which is 

 therefore continuous, and the purity of the 

 metal thus obtained is higher than has ever been 



attained by any other process. This process is 

 identical with that of Herault, which is carried 

 on at Neuhausen, on the Rhine, in Switzerland. 



In a paper on the industrial preparation of 

 aluminum M. A. Ditte says that the alkaline 

 aluminates are decomposed by water, and even 

 in the presence of an excess of alkali the intro- 

 duction of a few crystals of aluminum hydrate 

 into the solution suffices to prevent the establish- 

 ment of equilibrium and to effect the decompo- 

 sition of the aluminate. The rapidity of the 

 reaction may be increased by stirring. In the 

 industrial process of obtaining aluminum from 

 bauxite these crystals are provided by adding 

 to the sodium aluminate a little of the deposit 

 obtained by treating it with carbon dioxide in 

 the cold, a deposit which consists of crystallized 

 aluminum hydrate. The gelatinous hydrate has 

 no such effect. The alumina precipitated is very 

 pure. Substances such as silica and phosphoric 

 acid, dissolved out ot the bauxite by the caustic 

 soda employed, remain in solution. 



Files are now made containing a small portion 

 of aluminum mixed with the file steel. It is 

 claimed that this causes a great change in the 

 character of the steel. It renders the steel softer 

 when the file is cut, so that the teeth are much 

 cleaner and more evenly cut than with the ordi- 

 nary file ; and when the file is hardened it gives 

 the metal a toughness and hardness previously 

 unknown, so that the result is a file that will 

 do more work and with less clogging than the 

 ordinary tool. 



L. Grrabau ha? devised a process for supply- 

 ing aluminum fluoride in a sufficiently pure 

 state at a cheap rate, so that it can be advan- 

 tageously employed for the manufacture of alu- 

 minum. It consists in the employment of hydro- 

 fluoric or hydrofluosilicic acid with clay. "Pul- 

 verized calcined clay, or kaolin, as poor in iron 

 as possible, is introduced into dilute hydrofluoric 

 or hydrofluosiiicic acid with continual stirring 

 during the process. At the end of the reaction 

 the mass is neutralized, so that a drop of it 

 forms a pure yellow color with tropceleum. A 

 solution of aluminum fluoride is thus obtained 

 free from silicic acid. 



A method of coating aluminum with other 

 metals, described by Prof. Neesen, of Berlin, 

 consists in dipping the aluminum in a solution 

 of caustic potash or soda, or of hydrochloric acid, 

 until bubbles of gas make their appearance on 

 its surface, whereupon it is dipped into corrosive 

 sublimate to produce amalgamation. After a 

 second dipping into caustic potash till bubbles 

 of gas are evolved the metal is placed in a solu- 

 tion of a salt of the desired metal. A film of the 

 latter is rapidly formed, and is so firmly adher- 

 ent that in the case of silver, gold, or copper the 

 plate can be rolled out or polished. When coat- 

 ing with gold or copper it is well first to apply a 

 layer of silver. When thus treated the aluminum 

 may be soldered with ordinary solder. 



In the new method of Herr Borntrager for 

 the separation of iron and alumina both hy- 

 droxides are precipitated together, ignited, and 

 weighed as oxides. They are then redissolved 

 in hydrochloric acid, rendered almost neutral 

 with potash lye not soda and both oxides are 

 then reprecipitated with neutral liquid potash 

 soap. After filtering, the potassium chloride is 



