METALLURGY m 



Light alloys of aluminium have received much attention and marked progress has been 

 made. In the Ninth Report to the Alloy Research Committee the alloys of aluminium with 

 manganese and with copper plus manganese have been studied. Derived from the best of 

 these alloys is the metal known as duralumin, developed in Germany by Wilm; this alloy 

 contains from 3 to 4 per cent of copper and from | to 15 per cent of manganese together with 

 5 per cent of magnesium. This latter addition gives the alloy the remarkable property of 

 undergoing a gradual spontaneous hardening after suitable heating and quenching at first 

 the mechanical properties are unchanged, but in the course of four days the tensile strength 

 is doubled while the ductility is only slightly affected. In this hardened condition the alloy 

 combines mechanical properties similar to those of mild steel with a specific gravity slightly 

 less than 3, but these properties are destroyed by even moderate heating. This alloy was 

 used in the construction of the ill-fated British naval air-ship of the rigid type at Barrow-in- 

 Furness. Quite recently a detailed study of the alloys of aluminium with zinc and with 

 zinc plus copper has been published in the Tenth Report to the Alloys Research Committee. 

 One of the alloys there described, containing 25 per cent of zinc and 3 per cent of copper, 

 attains mechanical properties similar to those of steel or of duralumin but entirely without 

 any special quenching or other heat-treatment; this alloy, however, has a specific gravity 

 slightly higher than duralumin (3.25). The demand for materials combining strength with 

 lightness arising from aeronautical construction has given a fresh impetus to the study of 

 light alloys, and further important developments are to be anticipated. 



Gold and Silver, Platinum etc. Apart from the general tendency towards perfection 

 in detail, resulting in greater efficiency and increased output, few remarkable develop- 

 ments are to be recorded with regard to the precious metals. The cyanide process (E. B. 

 xii, 199) has received increased application, and is becoming standardised to some ex- 

 tent. A novel proposal was that of Clancy to replace the expensive alkaline cyanides 

 by the cheap product of atmospheric nitrogen fixation, calcium cyanamide, coupled with 

 the application of electrolysis. No large practical developments of the process appear 

 to have taken place as yet. Efforts are being made to render the cyanidation process 

 truly continuous, but the resulting gain is somewhat doubtful. On the other hand the 

 method of agitating slimes by means of air- jets is now wide-spread and successful. The 

 treatment of sulphide ores by this process is also receiving greater attention, and as the 

 chemistry of the process is better understood simplifications have become possible. 



In regard to the metallurgy of the remaining metals similar general tendencies have 

 manifested themselves, and only a few special matters need be referred to here. 



In connection with the use of lead for accumulator plates, or for any purpose where 

 large reacting surface area is desirable, the process invented by Hannover for producing 

 porous metals becomes of importance. Hannover utilises the fusibility of the eutectic 

 alloys by casting an alloy consisting for instance of lead and tin in such a way that the metal 

 consists of lead crystals whose interstices are filled up by eutectic; at a suitable temperature 

 this eutectic is fluid and can be expelled by such means as centrifuging, when porous lead 

 is left behind. Lead, tin, and especially zinc as required for the cyanide process, can now 

 be obtained in the form of "ribbon metal" produced by allowing a jet of the molten metal 

 to fall upon a rapidly rotating cooled iron drum; the metal runs off as a continuous flat 

 ribbon. By the use of very wide jets, sheet-metals can be produced in the same way. More 

 remarkable still is the process of Schoop, in which a jet of molten metal meets a jet of high- 

 pressure gas and is atomised so as to form a metallic cloud... This finely-divided metal can 

 be sprayed upon any object which it is desired to coat and yields a strong coherent deposit 

 which can be made either to adhere firmly to the matrix or to leave it in the form of a cast. 

 The metallic spray does not burn or injure even delicate articles, so that silk or wax can be 

 readily coated. Quite recently it has been found that finely-divided solid metal (powder) 

 can be similarly made to adhere and to cohere by a spraying process. 



In regard to zinc, the efforts at electric smelting are still being continued in Sweden, and 

 although it is considered in most quarters that the process is still in an experimental stage, 

 definite success, particularly in the production of spelter of high purity, is claimed. Ex- 

 tremely pure spelter, said to be of electrolytic origin, is at present produced in small quanti- 

 ties in England, but the demand for very pure zinc appears to be increasing. Efforts to meet 

 it are taking the direction of improved methods of refining, and although much secrecy is 

 observed, it is probable that vacuum processes of distillation are being introduced. 



Some reference must also be made to the advance in the metallurgy of the very refractory 

 metals, such as chromium, molybdenum and tungsten. The latter metal is now produced 

 in approximate purity by the electric furnace, and for the purpose of electric incandescent 

 lamps drawn tungsten wire is now used in place of the agglomerated filaments formerly 

 employed. Both tungsten and molybden find increased uses in "high speed" tool steels, 

 while chromium is finding a wider application in the production of new alloys. Among 

 these an alloy of nickel, with chromium and manganese, known as "nichrome," has achieved 



