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theories enable the chemist more intelligently to control the materials used in automotive transportation, but few really revolutionary advances have been made, within the period in which automotive transportation has become so highly developed, in the nonferrous alloys dealt with in this paper. Most of them were known and rather far developed even before the days of automotive transportation. It was necessary only to adapt them to automotive uses, and to produce them of uniform high quality at reasonable prices. That little of the spectacular can be recorded for the copper and other alloys dealt with in this paper seems to be accounted for by the fact that the older chemists and metallurgists who developed those alloys did a good enough job so that the products were adequate for the demands of the automotive industry. In the alloy-steel and the aluminum industries the demands of automobiles and aircraft forced great de-
Vol. 19, No. 10
velopments upon those industries so that spectacular achievements can be recorded in the production of new alloys or those not previously developed commercially. The nonferrous metallurgist has been called upon to solve such problems as how to use more borings in his furnace charge and still make good carburetors, or how to modify the composition of the alloy so it will machine a trifle more readily, rather than to introduce radically new alloys like stainless steel, molybdenum steel, or the aluminum-silicon alloys. Most of the advances in the nonferrous fields that concern automotive transportation and are discussed here, are small hard-won gains resulting from steady plugging along. The chemist and metallurgist have made, and will continue to make, these miscellaneous nonferrous metals and alloys for automotive use a little better, a little more uniform, and a little cheaper.
Aluminum and Its Alloys By Francis C. Frary ALUMINUM COMPANY OF AMERICA, XEWKENSINGTOS, PA.
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ETALLURGY is essentially a branch of applied chemistry : its problems are fundamentally chemical, although in many cases the greater physical prominence of the mechanical side of a metallurgical problem tends to obscure its chemical features. In the case of the production of aluminum, however, the chemical problems are more prominent and their solution relatively more difficult than in the case of any other common metal. Here it is impractical to use the familiar and chemically simple reduction of the oxide by carbon or carbon monoxide, which plays such a role in the metallurgy of iron, copper, lead, zinc, and tin. We must bring to our aid more powerful chemical reducing agents, such as the alkali metals, or else we must carry out the reduction by electrical means. Deville and others worked along the first of these lines, achieving a technical and commercial success in the reduction of sodium aluminum chloride with metallic sodium, but when Hall found out how to solve the problem along the second line, Deville’s method became commercially valueless because of its intrinsically higher costs. Chemical Problems
The first chemical problem in the electrolytic production of aluminum was to find a solvent in which the electrolysis of aluminum oxide could take place. Hall solved this by the use of molten cryolite. The next great problem was the cheap production of the oxide on a large scale in a state of purity comparable with that of many c. P. chemicals. The sodium aluminate process, as developed by Bayer and worked out in detail by groups of unknown chemists in plant laboratories, was the first real solution of this problem, and has made most of the world’s supply of alumina. A host of other inventors have labored on this problem and presented many and varied alternative solutions of it. While most of their processes are chemically possible, they are practically all commercially impossible in competition with the Bayer process. Hall himself blazed the trail along what appears at present to be the most promising of these other lines of attack-namely, the electrothermal purification of bauxite, and it appears probable that one or more commercial solutions of the problem along this line are now in sight. The production of synthetic cryolite, the chemical problems of the carbon mix for the inert crucible lining, and the prob-
lems of carbon-electrodemanufacture have for years engaged the attention of chemists. The aluminum industry probably manufactures and consumes a t least half of the carbon electrodes of the world, and has contributed much to the development of the technic of this industry. Although commercially pure aluminum is used in the wrought condition for molding instrument parts, body parts etc., and can be considerably hardened by cold-working, an important problem has been the development of methods for very largely increasing its hardness, strength, and elastic limit, especially when it is to be used in the form of castings or wrought metal parts which may be highly stressed in service. This has been accomplished by alloying it with small amounts of other metals, especially copper, zinc, silicon, magnesium, and manganese, and by heat-treating some of these alloys. The value of copper and zinc in aluminum-casting alloys has been known for many years, and most of the aluminum castings used in the automotive industry contain one or both of these metals as important constituents. Silicon alloys are now coming into quite extensive use, thanks to the labors of Aladar Pacz, whose “modification” process for these alloys is a good example of the profound effect which the presence of a trace of one element (sodium) may have on the behavior of another (silicon) in an alloy. Magnesium is useful in some classes of heat-treated alloys, and the manganese alloys are found to be particularly resistant to corrosion. Recent Developments The recent development, by Archer and Jeffries, of the proper technic for heat-treating aluminum-copper alloy castings promises to be of great interest to the automotive industry, especially in view of the increasing demand for greater engine reliability for motor busses, etc. Crankcases for the largest fire engines are made of such heattreated castings. Similar castings are replacing the ordinary aluminum castings in engines and other parts for busses, and are becoming of increasing importance in other places in the automotive industry. The development of the high-strength wrought alloys of aluminum, having properties allowing them to replace mild steel, owes its start and much of its success to the pioneer work of a German metallurgist, Alfred Wilm, who dis-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
covered the heat treatment of aluminum-copper alloys. The alloys of this type, chiefly used in this country for automobile parts, such as connecting rods, were developed here by Archer and Jeffries. The ease with which these alloys can be forged makes practicable the use of such forgings for anything from hood-latches to airplane propellers. Their development is a striking example of the value of a painstaking laboratory investigation of the cause of an obscure chemical phenomenon (precipitation of copper and Mg,Si from solid solution) and a careful study of the alloy systems involved. The present theory of the heat treat-
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ment is based on the careful researches of Merica, Waltenberg, and Scott, at the Bureau of Standards. Future Problems
The world’s chemists and metallurgists will be busy for a long time in speeding the development of this, the youngest of the common metals, reducing its cost, and increasing its field of usefulness. The automotive industry, on account of increasing fuel costs, is bound to receive more and more benefit from their labors, and its demands will furnish the incentive for many new researches.
Rubber Chemistry’ By William C. Geer2 150 VALLEY ROAD,N E W ROCHELLE, N. Y.
N THIS age of automotive transportation one may well meditate for a moment upon the factors which have contributed to its spectacular growth. Expanding as it has within our own generation, we are inclined perhaps to overlook its origins and the contributions to its success given by that ever necessary, usually comfortable, though at times exasperating, article called the rubber tire. And the world has heard but little of the rubber chemists, a quiet group of men, by whose efforts it and other rubber products have been brought to so high a degree of serviceability. An automobile. namely, a horseless carriage, is no new conception. There was such in China before 1600. Again, in the early part of the eighteenth century in France a mechanical vehicle was invented and for a day played its little part in the scheme of transportation. The period from 1800 to 1835 was a busy one for steam engineers, who created the first interurban passenger bus which made regular trips between London and Stratford. Why, the question may well be asked, did not the steam carriage extend its service and why did it soon leave the more convenient highways to run over iron and steel rails? One reason at least is definite. These early vehicles had no cushions on the wheels and they rapidly jarred themselves to pieces upon even the best of Roman roads. They were truthfully called “bone-shakers.” To be sure, a solid rubber tire was tried in those days, but it was made from crude rubber, a soft, rapidly wearing substance, for vulcanization had not been discovered and the rubber chemist was then unborn. So the steam vehicle took t o rails upon which its service expanded; and thus, perhaps, the railroad owes its early growth to the lack of rubber chemistry and the automobile, to its discoveries.
I
Complex P r o b l e m s of t h e R u b b e r C h e m i s t
The business of the rubber chemist is confused by a loose terminology because the word “rubber” means three distinct groups of products. (1) Crude rubber, a plastic solid made from a milky sap which flows from certain trees which grow in the tropics. ( 2 ) When mixed with small amounts, say 3 t o 5 per cent of sulfur, and with other substances and heated or vulcanized, this material alters its properties, becoming stronger and more cerviceable, but the product, though radically changed, still is called This article is respectfully dedicated by,the author to I,. M. Dennis. I t will be reprinted as Article No 5 in the Louis Monroe Dennis Quarter Century Volume, to be published in 1928, in commemoration of the completion by Professor Dennis of twenty-five years of service as head of the Department of Chemistry at Cornell University. 2 Formerly vice president in charge of Research and Development, The B. F. Goodrich Company, Akron, Ohio, 1
rubber, or soft rubber. It has come into our economics in the form of numerous articles, among them certain essential parts of the automobile tire, inner tubes, bumpers, window trim or shackle blocks. Indeed, comprehended as soft rubber, is the major portion of what the world understands as rubber. (3) When, however, some 30 or more per cent of sulfur is mixed with this crude rubber and the mixture heated over longer intervals of time there results a hard, tough body known as hard rubber, or preferably by the word “ebonite.”
The rubber business presents to the rubber chemist intricate problems. To form rubber articles, mixtures of several substances are made. The tread, for instance, of an automobile tire must be composed of a number of different ingredients. I n the formulation of these mixtures, or “compounds” as they are termed, a large variety of materials may be employed. They may be grouped into ten classes. (1) Crude rubber of which there are many grades. Every mixture is supposed to contain some crude rubber. ( 2 ) Sulfur which is placed as a division by itself because it is the one known substance necessary to the process of vulcanization. (3) . Certain dry powders, or pigments, such as carbon black and zinc oxide which have a decided reenforcing or toughening effect in rubber mixtures. (4) A still larger number of pigments, usually neutral in character, diluents, if you will, whose purpose is for different applications. ( 5 ) Again there is a group of substances of an inorganic nature such as litharge, lime and magnesia, which stiffen mixtures as well as speed the time of vulcanization. (6) Colors of a large variety. (7) Oils and waxes which give definite and desirable properties. (8) A large group of organic substances discovered during the last twenty-five years, called organic accelerators, the purpose of which is to speed the time of vulcanization and to give to the vulcanized article desired characteristics, such as increased toughness and resiliency. (9) At the moment coming actively into the rubber chemists’ picture is a group of organic compounds known as antioxidants, the purpose of which is to prevent deterioration of the vulcanized rubber and thus extend its life from but a few months without such a substance to many years if it be used. (10) Finally, is the group of reclaimed rubber, namely, old scrap tires, hose, etc., which have been chemically treated in order to free them from cotton fabric and produce a plastic homogeneous material capable of mixing with advantage into rubber mixtures.
In total, the number of chemical individuals in these ten groups of substances is several thousand. The task of the rubber chemist is not alone to know the chemical and physical nature of each of these materials. His business is complex in the extreme, for he must combine and select from these thousands, in order to create differing mixtures each of which after vulcanization may possess definite physical
