METALLURGY. 



625 



tory of the Charlottenburg High-School, Ber- 

 lin. The physical properties determined were : 





Magnesium can be best worked when heated 

 to 212 Fahr., at which temperature it can be 

 easily pressed, rolled, and drawn. More diffi- 

 culty is encountered with this metal when cast- 

 ing or soldering, as the melting and boiling 

 points are only a few degrees apart, and the 

 loss by oxidation is large. The molten metal 

 does not fill the molds so perfectly as aluminum, 

 and the castings obtained are always rough- 

 surfaced, and have air-holes. The difficulty 

 in soldering magnesium comes from the fact 

 that it can not be easily kept free from oxidiz- 

 ing, and even the slightest layer of oxide ren- 

 ders the soldering more difficult. The same 

 difficulty is also encountered, and has not yet 

 been wholly surmounted in the case of alumi- 

 num. The two metals show little dissimilarity 

 in their susceptibility to atmospheric influence 

 provided the magnesium is pure. Magne- 

 sium can be easily worked in the lathe. It 

 can be engraved and polished, and rolled in 

 complicated sections. The alloys of magne- 

 sium are beautifully bright and of fine color, 

 but are easily affected by atmospheric influ- 

 ences, and brittle. Hence they are ill-adapted 

 for technical purposes. 



The experiments of W. J. Keep upon the 

 influence of aluminum "on cast-iron have de- 

 termined several important points. It is known 

 that fused iron of any kind that would make 

 castings that would be full of blow-holes, will 

 make solid homogeneous castings if as small 

 a quantity of aluminum as 0*1 per cent, is ad- 

 ded just before pouring, and that such addition 

 causes the iron to remain fluid long enough to 

 allow of its being cast into molds. The measure 

 of the improvement is represented by a gain 

 of about 44 per cent, in resistance to weight, 

 and of 6 per cent, in resistance to impact. The 

 castings appear of slightly finer grain, and the 

 character of the crystallization is somewhat 

 different, but " the secret of the strength lies 

 in the closing of the spaces between the grains 

 or, in other words, in the increased solidity 

 of the casting." It had been a question whether 

 the aluminum remains in the iron to exert an 

 influence when the iron is remelted. To this 

 the experiments gave an affirmative answer. 

 As to the effect upon the grain of the changing 

 of the carbon from the combined to the gra- 

 phitic state, "aluminum allows most of the car- 

 bon to retain its natural combined form until 

 the metal is too thick for the separated carbon 

 to escape, but at the instant of solidifying alumi- 

 num causes the iron to drop a portion of its 

 carbon from the combined state. This liber- 

 ated carbon takes the graphitic form, and is 

 imprisoned in the otherwise solid iron. The 



advantages arising from a change of carbon 

 from the combined to the graphitic state, at 

 the instant of crystallization, are that all of the 

 carbon thus liberated is imprisoned uniformly 

 throughout the casting, and is not accumulated 

 in pockets, forming soft and hollow sp< 

 would be the case if liberated while the cast- 

 ing was yet fluid. Aluminum, more than any 

 known element, accomplishes this. Aluminum 

 takes away the tendency to chill, prevents the 

 formation of sand-scale, and modifies the hard- 

 ness of the iron by refining its grain so that it 

 may be more easily cut than iron of coarser 

 grain. It increases the resistance, or strength 

 to sustain a constant load, and in a greater de- 

 gree the resistance to impact. A gain is ob- 

 served in elasticity, while the fineness and 

 compactness of iron alloyed with aluminum 

 gives less permanent set than iron equally soft 

 when such softness is produced by silicon. 

 Aluminum when a sufficient quantity is ad- 

 ded takes off or reduces shrinkage ; but the 

 first additions of it seem to cause shrinkage, 

 through the closing of the blow-holes. The 

 tests for influence upon fluidity gave less defi- 

 nite results. The experiments were made sep- 

 arately with a white iron, in which the carbon 

 is combined, and with a Swedish gray iron, in 

 which the carbon is in the form of graphite. 

 The results were modified according as these 

 different qualities of iron were dealt with, but 

 mostly in degree, and not essentially in nature. 



Copper. For extracting copper from its py- 

 rites, Mr. M. J. Pering dispenses with the un- 

 pleasant and tedious roasting of the pyrites, 

 and finds an excellent substitute for it in the 

 property possessed by ferric nitrate of oxidiz- 

 ing, at temperatures between 122 and 302 

 Fahr., the copper sulphide of the ores direct 

 to copper sulphate. The pulverized copper 

 pyrites is intimately mixed with ferric nitrate, 

 and the mixture is exposed to a temperature 

 of 105 Fahr. Nitrous fumes at once begin to 

 be evolved, and copper sulphate to be formed. 

 "When the temperature is gradually increased 

 to 212 and 302, there results, after washing 

 with water, pure copper sulphate, without a 

 trace of iron, while the residue consists of un- 

 altered iron sulphide, silver sulphide, and the 

 ferric oxide produced from the ferric nitrate. 

 From this the silver may be extracted by 

 means of Russell's process, and the subsequent 

 residue used for sulphuric-acid manufacture, 

 and finally for iron-smelting. 



Copper-wire has special adaptations for tele- 

 graphic service in its great mechanical strength 

 when it is hard drawn and pure and its virtual 

 freedom from those effects of electro-magnetic 

 inertia that tend to throttle the flow of elec- 

 tricity through iron-wires. Several wires have 

 been put up on the line from London to Dub- 

 lin, with results that exceed the most sanguine 

 expectations of the projectors. So much de- 

 pends on the care and accuracy with which 

 copper-wire is erected, that an entirely new 

 mode of putting it up has been adopted, in 



