METALLURGY. 



to attention by Matthiessen thirty years ago ; and 

 the investigations of Graham have shown that solid 

 metals are true solvents for gases, which move and 

 diffuse freely in them, sometimes to reappear with 

 gaseous elasticity. The experimental portion of 

 Graham's work was conducted by Prof. Roberts- 

 Austen, who has given some of the results he 

 reached in the Bakerian Lecture of the Royal So- 

 ciety and in " Nature." The experiments show that 

 metals diffuse in one another just as salts do in 

 water. Tables are given showing the diff usibility 

 of certain metals as gold, silver, lead, rhodium, 

 and platinum, in lead, tin, bismuth, and mercury, 

 in square centimetres per day. A method is de- 

 scribed by which it is shown that molten metals 

 actually pass into one another by diffusion. The 

 belief has long been prevalent that diffusion can 

 take place in solids, and is supported by the prac- 

 tice in conducting important industrial operations, 

 as in the " cementation " process employed in steel 

 working by the carbonization of solid iron, and in 

 that for the removal of silver from a solid gold-silver 

 alloy. The electro-deposition of metals also affords 

 evidence of their interpenetration. The author ob- 

 served in 1887 that an electro-deposit of iron on a 

 clean copper plate will adhere so firmly to it that 

 when the metals are severed by force a copper film 

 is stripped from the copper plate and remains on 

 the iron. Mr. Edward Sonstadt gilded a platinum 

 crucible inside and out, when upon warming it the 

 color began to change as soon as the heat reached 

 the platinum, and the gilding had disappeared by 

 absorption before visible redness was attained. 

 Faraday and Stodart showed in 1820 that platinum 

 will alloy with steel at a temperature at which even 

 the steel is not melted. Evidence has long existed 

 of the volatilization of solid metals, and the fact is 

 confirmed by the experiments. Some of them, for 

 instance, furnish evidence that slow diffusion of 



fold in lead occurs at the ordinary temperature, 

 f clean surfaces of lead and gold are held together 

 in a vacuum at a temperature of only 40 F. for 

 four days, they will unite firmly, and can be sepa- 

 rated only by the application of a load equal to the 

 breaking strain of lead. The nature of welding, 

 however, remains to be investigated, as there is 

 probably interlocking of molecules and atoms, 

 which precedes true diffusion. Gold placed at the 

 bottom of a cylinder of lead 70 millimetres long 

 which is apparently solid will diffuse to the top in 

 notable quantities at the end of three days. At 

 100 the diffusibility of gold in solid lead can be 

 readily measured ; and experiments which are still 

 in progress show that the diffusibility of solid gold 

 in solid silver or copper at 800 is of the sajne order 

 as that of solid gold in lead at 100% 



In his elaborate researches npon the alloys of 

 copper and zinc, M. C. Charpy has found that if the 

 maximum temperature of annealing is maintained 

 for some time the mechanical and micrographical 

 properties of test pieces of similar composition de- 

 pend only on the temperature. Reheating has no 

 effect on the tensile strength of copper unless the 

 temperature exceeds 280 C., when there is a pro- 

 gressive lowering of the tensile strength until the 

 temperature reaches 420 C. Above that point a 

 further increase of temperature has no effect on the 

 metal, the annealing being complete. Finally, 

 when the temperature is so high that the copper is 

 " burnt," the tensile strength again falls off rapidly. 

 In tests made upon completely annealed bars, in 

 which all accidental differences were believed to be 

 eliminated, the author found that the tensile 

 strength increases with the percentage of zinc, 

 passes through a maximum when the alloy contains 

 about 45 per cent, of zinc, and then decreases rap- 

 idly. The elongation increases similarly with the 



percentage of zinc, but passes through a maximum 

 when the alloy contains 80 per cent, of zinc, and 

 then decreases rapidly. It follows that there is no 

 advantage in using for industrial purposes alloys 

 containing less than 30 per cent, of zinc, as they are 

 more costly, and possess less resistance and less 

 malleability than those richer in zinc. If more 

 than 43 per cent, of zinc is present, the alloys are 

 brittle. Thus only those alloys with from 30 to 43 

 per cent, of zinc can be recommended for use. 

 When the reheating is carried to a very high tem- 

 perature, near the melting point of the alloy, so that 

 it is " burnt " blowholes appear, increasing in num- 

 ber as the temperature rises and fissures develop 

 around the crystal, eventually forming a complete 

 network. The microscopic structure revealed by 

 etching polished surfaces makes it possible to divide 

 the alloys of copper and zinc into three classes, cor- 

 responding with certain proportions of the constitu- 

 ents. It enables the observer to determine whether 

 the metal has been cast, whether the casting has 

 been made at a high or a low temperature, and what 

 is the nature of the mold ; and shows the effect of 

 hardening, of annealing at various temperatures, 

 and whether or not the metal has been burnt. 



In order to obtain the best castings of aluminum 

 bronze, special care is taken not to overheat the 

 metal, for if it is heated at too high a temperature, 

 the aluminum will oxidize ; the oxide will make the 

 entire casting " dirty," and the metal will be spongy 

 from the presence of o'ccluded gases. The scum 

 which floats on the top of the melted bronze must 

 be prevented from going into the crucible, and the 

 shrinkage has to be counteracted. The last two 

 objects are secured by special provisions in the 

 apparatus. 



Alloys of refractory metals are obtained by M. 

 Moissan by projecting a mixture of the oxide with 

 powdered aluminum into a bath of liquid alu- 

 minum. The heat set free by the oxidation of the 

 aluminum has been found sufficient to carry on the 

 reaction. In this manner alloys of aluminum with 

 nickel, molybdenum, tungsten, uranium, and tita- 

 nium have been obtained. 



Reostene, a new resistant metal described in the 

 British Association by Dr. J. A. llarker and Mr. A. 

 Davidson, is an alloy containing iron and nickel. 

 Its specific resistance is higher than that of man- 

 ganese, being about 46 times that of Matthiessen's 

 copper. Its temperature coefficient is positive and 

 constant, and is equal to about O'OOll per degree 

 centigrade. 



New Processes. The new process for the direct 

 production of iron and steel from the ore intro- 

 duced in Sweden by Dr. De Laval is said to con- 

 sist in mixing pulverized iron ore with carbon, 

 and subjecting the same in a rotating cylinder to 

 heat, after which it is brought into direct contact 

 with an electric arc of immense power, which re- 

 duces the ore to metallic iron. The melted iron 

 then flows into a large and highly heated fur- 

 nace, where it can either be manufactured directly 

 into steel or cast in any suitable form for further 

 treatment. 



A new electrolytic process for the manufacture 

 of aluminum recently patented in Europe consists 

 in the decomposition by the electric current of an- 

 hydrous alumina rendered fusible by an appropriate 

 flux. The anhydrous alumina is dissolved in a 

 bath composed of fluorspar and chloride of sodium, 

 or of an alkaline silicate or an alkaline borate, and 

 decomposing the same in the solution by the elec- 

 tric current. 



A process, by Alexander Dick, for the production 

 of metallic bars by extension applies to the produc- 

 tion of all kinds of metallic sections, from thin wire 

 or plain bars to complex designs, by simply forcing 



