922 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 18, KO. 9

a large part of the entertainment. Both the production and progress to the improvements in electrical illumination projection of motion pictures are dependent on our modern during the past fifty years. It is constantly contributing to electric illuminants. Altogether, we owe a great deal of our our prosperity, progress, safety, comfort, and happiness.

Fifty Years’ Progress in Aluminum’ By Junius David Edwards

ALUMINUM COMPANY OF AMERICA, NEW KENSINGTON, PA.

N LOOKIKG back fifty years to the date of the founding of the AXERICAN CHE~V~ICAL SOCIETY, we are struck I by the fact that, practically speaking, the aluminum

industry did not then exist; it has reached its present state of development within the lifetime of the SOCIETY. In contradistinction to the other common metals, aluminum can only be produced by methods involving chemical and electrochemical discoveries and technic, and these are the reasons why it remained totally unknown to the human race until the early part of the last century. While its progress has been rapid in many ways, it nevertheless has made but a beginning, and the future is one of great promise.

Aluminum is the only common metal whose ores require an extensive and exhaustive chemical refining treatment to produce a chemically pure compound before its reduction to metal. Every other material consumed in its reduction must also be of the highest purity. The production of aluminum is particularly dependent, therefore, on chemical manufacturing and control processes. Men of an earlier age could and did produce iron, copper, gold, silver, lead, and tin by rule-of-thumb processes, but only the develop- ment of modern science makes possible the production of aluminum.

Preparation

First made by the Danish chemist and physicist, Oersted, in 1825, its early history was one of purely chemical de- velopment. The names of Wohler and Deville are closely associated with the production of aluminum by the reduction of aluminum fluoride and cryolite with metallic sodium. I n an effort to cheapen the production of aluminum, Castner discovered and developed his process for the production of sodium. Although the price of aluminum fell to about seven dollars a pound, this did not prove to be the solution of the problem. It remained for Charles M. Hall, an American chemist just out of college, to discover, early in 1886, the electrolytic process of reduction which marked the birth of an industry. The story of Hall’s persistent and successful fearch for a practical method of producing aluminum has already been told. In France, and at almost the same time, P. V. Heroult discovered substantially the same process as did Hall. The United States Patent Office, however, awarded priority of invention to Hall.

The preparation of a pure oxide of aluminum from the naturally occurring crude hydrate, bauxite, was worked out by Bayer. I n spite of the great variety of processes which have been studied and proposed by inventors in every land, substantially all of the aluminum oxide consumed by the industry is still prepared from bauxite by a chemical process involving the production of sodium aluminate (either by digesting bauxite with caustic soda or fusing it with soda ash) and its decomposition (by hydrolysis or precipitation with carbon dioxide) to form the pure hydrate, which is converted to the oxide by calcination. The nu- merous processes for extracting the oxide from clay, usually by digestion with acids, followed by purification and de-

1 Received May 27, 1926.

composition of the salts, seem to be inherently unable to compete with the Bayer process except under very excep- tional conditions. The electric furnace processes for re- fining bauxite have not been a commercial factor up to this time, but seem to have important possibilities of future development.

The preparation of purified alumina is in itself an immense chemical industry. The estimated production of 300 million pounds of aluminum in 1925 required the preparation of more than 600 million pounds of purified alumina. One works alone in the United States produces over 400 million pounds of alumina annually with an average impurity con- tent of only about 0.5 per cent, of which less than 0.1 per cent (silica and iron oxide) is reduced and appears in the metal.

The early years of the aluminum industry were largely occupied in solving the technical and engineering problems incident to establishing the electrolytic process on a com- mercial scale. To the versatile genius of Charles M. Hall, aided by the enthusiastic support of his associate, Alfred E. Hunt, is due much of the credit for this development. Many inventions, some patented but most of them not, were Hall’s contribution to the art. His faith in the future of aluminum was such that he confidently urged continued expansion, even though no immediate market for the metal was in sight. In recognition of his achievements Hall was presented with the Perkin Medal by the Society of Chemical Industry in conjunction with the AMERICAN CHEMICAL SOCIETY and the American Electrochemical Society in 1911.

When hydroelectric power became available in quantity a t Niagara Falls, the aluminum industry of this country moved there. However, with the constantly increasing demand for power, in and around our large cities, the center of production has moved to lower cost water-power cites. The latest of these developments is the establishment of new works on the Saguenay River, Province of Quebec, Canada, where there is a potential 800,000 horsepower waiting to produce aluminum.

Uses

Having learned how to make aluminum, there still re- mained the formidable problem df finding a stable market. For many years practically every use of aluminum was a new use. The producer was frequently forced into a manufacturing business in order to prove that aluminum could be satisfactorily employed for this purpose or that. Fabricating methods had to be devised or adapted, and the industry still finds it has countless problems to solve in the melting, casting, rolling, drawing, spinning, extruding, forging, ,pressing, machining, welding, soldering, and finishing of aluminum and its alloys.

The aluminum cooking utensil formed one of the first and best known outlets for aluminum. Singularly, one of the latest uses has been its extensive employment in electric household devices, such as the vacuum cleaner and washing machine.

Through the vision and inventive ability of William Hoopes the practicality of aluminum conductors for electric power

traiismissioii was ~lemoiistrated. Over lj0,oOO nriles aluminum coirductor are now in service and this sllhstanti~l total is rapidly being increased. Weiglxt for weiglit, alu- niinuin lias twice the conductivity of copper. An aluminum conductor of given capacity has a greater surface and eon- sequeiitly lower corona loss than a similar copper conductor. Its lighter weight permits further economies in tlie eoirstruction and rriiiriber of supporting towers required for a power line.

Aleminum found an early aud extensive use in the auto- mobile. Now that its usefulness has bccn dernonstrat~ed in tire modern and .. -~

u w e l forms of transportation, aircraft and the motor bus, t,he railroads are goiiig back to fundanrcnt,als to see diether alumiiium will not also solve many of their problems. Along still another line mention may be made of t he e n t r a n c e of aluminum-bronze po~~-dcr irrto the paint field.

Alloys

At the beginning of the twmtietll wutury the field of tlie possible em- ploymcnt of aluminum had been sur- rcyed in a broad way. Its uses for structural purposes were limited hy tlic physirill propcrt.ies available in tlic known wrought alloys which had n tcnsile strength of about 30,000 to 10,OOO pounds per square inch, with a limited duct.ility. About thia time :mi epoch-making discovery was mail(: by Alfred Wilm,2 wlieri hc found tlmt aluminum alloys of a particular con- pos i t i on were susceptible to 'Rent treatment of a novel character. Al- most at a stroke the a t t a i n a b l e s t r cng t l i of aluminum alloys was doubled. With aluminurn alloys ha,- ing the st,rengtli of mild steel aiid ndequate ductility, it is little wonder if metallurgists indulged i n some

querioliiug is to form a solid solution of certitiri of the elements, notably copper, in aluminum. Moreover, the atomic mobility is still sufficient., even at 20" C., to permit the excess dissolved material held in the quenched solution to pre- cipitate in the form of submicroscopic particles. This highly dispersed precipitate is responsible for the marked increase in strength and hardness of the alloy after aging.

The t,beory of Merica and his co-workers stimulated further rcsearcll in tlie ficld of heattreated allovs and it has

Charles M. Hnll 11863-19141 ~. This ptioto is from the scuipfuie hy

0. Morriti, a Pitfsburgh ~ u l p i o r . and i s cart from aluminum-siiieon anoY It is *,ow in t h e Carnegie hIvarum oi Piitslrurgh.

roseate dreams. Without more than an empirical knowledge of the meehan-

ism of his heat process, Wilrn developed one of the best (if the "sbrong" aluminurn alloys now available. Yet it remained for workers a t our o m National Bureau of Stand- ards to offer a satisfactory explanation of the heat treatment process. Wilm's alloy, which he called "Duralumin," contaius as its essential ingredients about 4 per ceut. copper, 0.5 per cent magnesium, and the silicon and iron present as impurity in the ingot aluminum, together with about 0.6 per cent added manganese. When the wrought alloy is heated to ahout 500" C. and quenchcd therefrom, it is in a metastable condition. On stauding at room iemperaturc it begins to harden almost immediately; after four days the hardening or aging is practically complete. The tensile strengt.h, which may have been, for example, about 45,WO pounds per square inch shortly after quenching, has increased to about 60,000 pounds per square inch on standing a t room temperature.

Merica, Waltenberg, and Scott,Z by an ingenious chain of reasoning based on their own experimental work, advanced tlie theory that the result of heating the alloy previous to

9 German Patents 170,085 (October 20, 1903) and 244.534 (March 20,

3 Bur. Slondovds, Bull. 16, 271 (1919); Trans. Am. Inst. Mia. Met. 1909).

E w . , 64, 41 (1Y20).

proved a fertile one iniced. Archer and Jeffries4 discovered that the hinary aluminum-copper alloys which aft.er quench ing do not age-harden sub- stantially at room temperature may be made to do so by heating at tem- perat,ures of about 100" to 175" C . A t the National Physical Laboratory in England it was discovered that aluminum alloys containing magnesium and silicon, hut without copper, age- h a r d e n a t room temperature after queaching from about .WOO" C.3 Cer- tain of the alumiiiuin alloys containing magnesium and silicon but without coppor are inore plastic and worknble tlrnn Duralumin and by quenching and then aging at an elevated tem- perature their strength and hardness are increased much more tluin hy room temperature aging.@ Archer and Jeffries also discovered how to lieat- treat, aluminum alloy castings to pro- cluc:e coirimercially valuable results. As a result of these inventions and their intensive development by the in- dustry new horizons have been opened for aluminum.

-4s an interesting comment, up to about 1020 silicon had been generally considered an undesirable element in aluminum. Now that its nromr use . . and possibilit,ies are better undcrstood, i t has quickly taken its place as one of

thc important alloying elements. Aladar Pacz' directed the at,tcnt,ion of aluminum metallurgists to the aluminum- silicon alloys by his invention of a process of modifying tlre alloy structure hy treatment of the molten alloy with sodium fluoride. This "modification" process is an interesting and novel example of "colloidal metallurgy." Two or three lrundredths of a ncr cent of metiLllic sodium introduced into the molten alloy before castiug increases its tensile strength by 50 per cent and the ductility by several hundred per Aside from this development, which has not yet found ex- tensive use, silicon was found to have valuable alloying properties from the staidpoint of facilitating casting proc- esses; its use has almost revolutionized aluminum die-casting.

Although a practical process of refining impure aluminum has long been desired, it is only ivithm the last five years that i t lias become an actuality. William Hoops, in co- operation with the research staff of the Aluminum Company

~ m . inst. .win. M ~ L . EW., 71, 828 (1925). 4 U. S. Patent 1,472,738 (applied for December 20, 1921); Tranr.

f Henroii and Gayier, J. In# Mctoli, 18, 321 (1021). 6 Archer and Jeffries, U. S. retent 1,472,739 (applied for December

7 U. S. Patent l,3S7,9W (appliedforFebruary 13, 1920). 6 Edwards and Archer, Chcm. Met. Eng., 81, 504 (1924); Edwsrds,

Yrary, and Churchill, U. S. Patent 1,410,461 (applied for November 27. 1s201.

20, 1921J.

924 IiVD USTRIAL AND ENGINEERISG CHEMISTRY Vol. 18, S o . 9

of A m e r i ~ a , ~ devised and put into successful operation a refining process similar in principle to an early proposal of his own and a later patent of Anson G. Betts.Io In this process a heavy liquid anode of aluminum-copper-silicon alloy and a cathode layer of liquid aluminum are separated by a layer of fused electrolyte of intermediate density. The three molten layers are thus superimposed on each other in the order of their densities. Current passing from the lower anode layer selectively dissolves pure aluminum and deposits it on the upper cathode layer. For the first time since the inception of the industry, aluminum of a purity as high as 99.98 per cent has become available. It is too early to predict the uses this high-purity metal will have in the industry; it has, however, been invaluable in the scientific study of the properties of aluminum and its alloys. The modern development of alloys is particularly

9 Hoopes, U. S. Patent 673,364 (applied for September 1, 1900); Hoopes, Frary, Edwards, Horstield, U. S. Patents 1,534,315, 1,534,317, 1,534,318, 1,534,319, 1,534,320, 1,534,321, 1,534,322 (all applied for Decem- ber 21, 1922). See also Frary, Trans. Am. Electrochem. Soc., 41, 276 (1925).

$0 U. S. Patent 795,886 (applied for April 1, 1905).

concerned with the effects of very small amounts of alloying elements. The use of high-purity aluminum permits the study of such effects without the confusing presence of the appreciable amounts of iron and silicon always existing in aluminum made by the Hall process.

Conclusion

In the United States and Canada a production of about 40,000 pounds of aluminum per year, in 1890, has grown to over 200,000,000 pounds today. As statistics, these figures are imposing, but no more so than would be the com- plete story of the technical development of the aluminum industry. This brief review has touched upon only a few of the more interesting and outstanding technical and com- mercial milestones of progress, but mention must be made of the indispensable efforts of the technical staffs of the producers, which have brought these and other inventions to commercial fruition. With the tools of research made available by modern physics and chemistry, it is not too much to expect that the next fifty years will be equally impressive.

The Role of Chemistry in the Manufacture of Silk' By Walter M. Scott

CKENEY BROTHERS, SOUTH MANCHESTER, CONN.

HE introduction of the technically trained chemist into the textile industry, and particularly into the silk T branch of this industry, is a comparatively recent

event. Fifty years ago no article could have been written on this subject and, in fact, no one would have attempted to write such an article, because chemistry was not even thought of in connection with silk. Ten years ago the chem- ist had progressed far enough so that he was in a position a t least to write an apology, defending his entrance into the silk industry chiefly from the standpoint of the number of problems waiting to be solved, and prophesying great things for the future. At the present time, although it cannot be truthfully said that we have arrived a t a complete under- standing of all the processes of silk manufacture-still we can, with a reasonable amount of pride in our profession, assert that the application of the principles of chemistry has pointed the way to the solution of a number of these problems.

At the very beginning the chemist had to possess more than the usual amount of temerity, which is generally ascribed to him, to expect to make any impression on an industry that had been in continuous operation since the dawn of history. We have authentic evidence that in the early ages the cultiva- tion of the silk worm and the manufacture of silken fabrics were placed under the direct supervision of kings and emperors, and they were even dignified by occupying a space in the writings of the famous Chinese philosopher, Confucius, who lived about 500 B. C.

Ever since the beginning of time the processes involved in the manufacture of silk have been jealously guarded. I n the early days in China the cultivation of silk was made part of a religious ceremonial and there was a penalty of death for anyone who divulged the secrets of the art to un- authorized persons. During the Middle Ages in Europe there were developed very powerful guilds of silk workers, to

which a man was admitted only after many years of appren- ticeship. Even fifty years ago the idea of handing down the secrets of the trade from father to son still persisted, particu- larly among silk dyers and finishers. These people were naturally opposed to having their formulas and processes analyzed and interpreted by an outsider, and equally so to making any radical changes in the methods that they had been using for many years.

Fortunately, an outside influence came to the aid of the chemist. The gradual development of synthetic dyestuffs during the past fifty years necessitated radical changes in dyeing procedure and paved the way for the scientifically trained man to work out new methods of application to fit the new types of coloring matters. Finally, the readjust- ments brought about by the World War, including the threatened famine of dyestuffs in the early years of the war and the gradual substitution of American types for the corresponding German ones, left the chemist more firmly en- trenched than ever.

Naturally, the persons most interested in the advent of the chemist in the silk industry were the silk manufacturers themselves. They felt, and rightly so, that it was up to the chemist to show that his knowledge could be applied to their problems so as either to improve the quality of their goods or to decrease the cost of their production. The fact that more and more chemists are finding a place in this industry is a good indication of the value placed upon them at the present time by all progressive manufacturers. However, in order to give an intelligent idea of the contacts that have been established between chemistry and silk, we will now take up in detail the various processes that are involved in the trans- formation from fiber to fabric.

Raw Materials

Presented in part before a joint meeting of the American Section of the Societ6 de Chimie Industrielle and the Society of Chemical Industry

Before starting upon what be termed the career of and the New York Section of the American Chemical Society and the Amer- the let us pause for a moment to consider the constitution ican Electrochemical Society, New York, N. Y., May 21, 1926. of the raw material. The pure silk fiber, which is called