September, 1926
INDUSTRIAL AND ENGINEERIA-G CHE-VIXTRY
preventing losses of plant food and bags by faulty operation, with the ultimate result of profits to the industry. Further Problems for Chemistry
Whether or not chemistry will solve the problem of concentrating plant food elements by eliminating the excess material other than what is recognized as plant food without destroying the real agricultural value of materials, time and experience can only tell. We must, however, guard against what is well illustrated by the old story of the professor, who talking to a group of
943
farmers, said: “Gentlemen, some day your fertilizer will be delivered to you in pellet form which you can put in your vest pocket. One inquiring farmer replied ‘Yes,’ and can we put the crop in the other vest pocket’?” Conservation is necessary, concentration perhaps, but let us be sure that some of the materials now used which have plant food elements in less concentrated forms do not carry elements which, while they may not be direct plant foods, have an influence on conditions which make for real fertilization, with the ultimate result that the crop secures its nourishment from a source which can be best assimilated.
A Half-Century of Progress in the Glass Industry‘ By George W. Morey GEOPHYSICAL LABORATORP, WASHI~YCTOS, D. C.
HE art of the glass-maker dates from the earliest antiquity. Its beginnings are shrouded in mystery; whether the first glass-makers were the Phoenicians, who undoubtedly carried on a considerable nianufacture, or whether the credit for founding the industry ip to be given to earlier Egyptian priests, is a moot question. Certain it is that glass objects, of essentially the coniposition of modern plate or bottle glass, have been found in tombs dating back to 3500 B. C. Glass was known to most of the early civilizations of historic times. Memphis was a glassmaking center; Alexandria possessed glass factories, producing not only blown ware but also splendid mosaics; and Rome was long a center of the art. The glass-makers’ guild a t Murano, near Venice, was a descendant of the Constantinople craftsmen, and Venice developed into the dominant glass center of medieval times. The industry was established in France and Germany in the fourteenth century, and the invention of cast plate glass was made in the latter part of the eighteenth century; the great plateglass works of St. Gobain finds the beginnings of its history in this invention. But during all these centuries only one type of glass was known, soda-lime-silica glass, modified, of course, by the very considerable amounts of impurities that crude manufacturing methods made unavoidable. Cntil recent times glass manufacture has been based on tradition as opposed to scientific knowledge, and the beginning of the period of knowledge was only fifty years ago. Before that time, to be sure, the types of glass had been increased by the addition of potash to the soda-lime crowns, and by the discovery of the flint-that is, lead-containingglasses. Some pioneers, notable among them Faraday, Harcourt, and Fraunhofer, had attempted to broaden the basis of glass technology by the introduction of other chemical elements. These early attempts were without influence upon manufacturing practice. Not until Schott began the systematic studies which were to develop into industrial practice can the modern period of glass technology be said to have begun. It may be thought that the achievements of Schott and Abb6 and their co-workers a t Jena have been over-emphasized in the historical literature of glass-making, but they represent a development which is not to be minimized. Before their time glass compositions were restricted to the crown-flint series, varying from the crown glasses, containing lime and silica with either soda or potash, or both, to the alkali-lead-silica glasses. Contrast these five oxides with the present ingredients available to the glass-
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Received June 7 , 1926
maker, which, in addition to those just named, include barium oxide, boric oxide, magnesia, alumina, zinc oxide, antimony oxide, phosphoric oxide, and fluorine. Most of these additions to glass-making materials were made by Schott, and of them the most noteworthy are boric oxide and barium oxide. Barium oxide has had its chief application in optical glasses, and our modern high-speed lenses were made possible by the development of the barium crowns and flints. Boric oxide also is an essential ingredient in many optical glass types; but more extensive are its applications to industrial glasses, laboratory glassware, and thermometer glass. Laboratory Glassware
The development of laboratory ware is of particular interest to chemists, and no field of glass technology has witnessed greater strides. Stas realized the necessity of more resistant laboratory ware for those atomic weight researches which still command our admiration, and in 1868 he caused experimental meltings to be carried on under his direction until a satisfactory glass was obtained. But the industry was not yet in a position to appreciate the need, and until Schott again took up the problem resistant laboratory glassware was not on the market. The glass developed by Stas was a potash-soda-lime glass, high in silica, and difficult to manufacture. The Jena workers studied the effect of addition of other ingredients, and the alkali-zincalumina-borosilicate glasses, typified by the well-known Jena “Gerate,” were the result. It is a n interesting fact that for most of the uses to which glass is put the quality is better the greater the number of ingredients. This is easily explicable in the matter of tendency toward devitrification, but why it should be true of chemical resistivity it is hard to understand. The excellent qualities of glasses of the type of Jena Gerate speak for themselves, and they remained the standard for many years, until the development of the American glass, Pyrex. This also is a borosilicate, but is exceptionally high in silica (over 80 per cent), is almost alkali-free, and has a low thermal expansion. Thermometer Glass
Another problem whose solution is largely the work of Schott and his co-workers is that of a satisfactory thermometer glass. Here it is no longer true that in many ingredients there is safety, for a satisfactory thermometer glass contains but one alkali oxide, Whether it be potash or soda seems to make little difference, but a mixed soda-
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INDUSTRIAL A N D EA'GINEERING CHEMISTRY
potash glass exhibits a thermal after-effect which causes the zero of a thermometer to change every time it is heated, and to recover but slowly, so that the zero point is continually drifting. Here also boric oxide is of great value. as the borosilicate type of thermometer glass can withstand higher temperatures without deformation, and greater and more sudden changes in temperature without breaking, than can the glasses free from boric oxide. Optical Glass
Vol. 18, No. 9
Kow enormous cylinders are drawn by machinery and blown by compressed air, and the hand-blown window glass is rapidly passing. For two centuries plate glass was melted in huge pots, which were lifted from the furnace and from which the glass was poured out upon iron tables and rolled flat with a roller. Now a large proportion of the plate glass is drawn directly from a continuously operated tank in a great sheet, and oftentimes used without the laborious grinding and polishing operations, though it is questionable whether the finest grades of plate can ever be so obtained. The use of boric oxide and barium oxide in optical glasses The enormous electric-light bulb industry, manufacturing has been mentioned, and they have revolutionized the millions of bulbs, would be almost unthinkable without design of optical instruments. Before the introduction of modern automatic bulb machinery, which takes t.he glass out of the furnace, in amount the modern glasses, the lens dedepending on the size of bulb to signer had a t his disposal only be made, lets it cool for the g 1a s s e s having practically a necessary time, blows it into linear relation between refractive shape, and delivers it annealed, index and dispersion; fixing the without the aid of human hands refractive index fixed the disperbut almost with human intellision, and full achromatization of gence. And so with other forms a lens system could not even apof b l o w n w a r e . Automatic proximately be obtained. Now machinery not only blows the the lens designer can choose from glass into shape, which was a a three-dimensional glass field; process relatively easy to make glasses with the same dispersion automatic, but also gathers it but widely differing indices are from the tank, by processes that available , and correspondingly are of more recent invention. glasses of the same index but Such automatic methods would different dispersions. These are not be possible without the most made possible by the introducrigid control of composition and tion, not only of barium oxide temperature. Any random sodaand boric oxide, but of still other lime glass, even though it may glass-making oxides, notably zinc be suitable for hand operation, oxide, magnesia, alumina, antiwill not do. The glass for an mony oxide, and phosphoric automatic machine must have oxide. Even these, however, do the proper viscosity and surface not completely fill the need of tension a t the feeding end, in the lens designer, who looks with order that the proper weight of envy on the relation between glass may be delivered without index and dispersion of some of folds or flaws; and must have the minerals. Especially worthy the proper viscosity-temperature - of mentiom among these is the curve, not too hard when blown, mineral fluorite (CaFZ), largely and not too soft when delivered used for the apochromatic lens Glass Blowing in the Old Days from the mold. To maintain systems-that is, systems in such properties requires ceaseless which the color correction has been so improved as to be almost perfect. An approach to control and accurate knowledge of the effect of each constitufluorite has been made in the fluor-crown glasses, which ent of the glass. The chemist has been able to meet these decontain a considerable percentage of fluorine, and have much mands, but unfortunately to a large extent by cut-and-try smaller dispersion than can be obtained in fluorine-free glasses. methods. The industry needs fundamental research which will There is still a great need ^for improvement, however, es- reveal the part played by each factor in the multi-component pecially in the direction toward fluorite, and it is hoped that system that constitutes a silicate glass, and the effect of each constituent on the properties of the glass, together with their further progress in this direction can be made. change with temperature. Of particular importance is Commercial Glass Production the effect of small alterations of the batch composition, But these improvements have all been largely directed such as substituting a small amount of magnesia for a corretoward the special glasses, which make up but a small pro- sponding amount of lime, or adding 1 or 2 per cent of portion of commercial glass production. Window glass, alumina; and of the presence in the glass of volatile conplate glass, and blown glass constitute the great bulk of stituents, such as water, carbon dioxide, halogens, and sulfur manufactured glassware, and improvements in these lines trioxide. We know these are always present. Are they are of great value. These manufactures have indeed been beneficial or deleterious7 1f7e do not know. Glass presents the anomalous condition of one silicate revolutionized in the past quarter-century, but chiefly along mechanical lines. However, chemistry has made the revo- mixture being melted in containers made of another silicate lution possible, for these improved manufacturing methods mixture, and resistant refractories are a matter of grave impose far more stringent demands on the glass furnished concern to the glass-maker. When all glass was melted in clay pots, the greatest ingenuity was exercised to improve than was the case in the past. Until recent years all window glass was blown by skilled their quality, and in optical-glass manufacture the pot is operators into cylinders, which were later cut and flattened. still a source of great difficulty. The introduction of the
I;1'DL-STRIAL 4 S D ELYGISEERISG CHEJIIIXTRY
Septeniher, 1926
porcelain or semi-porcelain type of glass pot was a wartime development in America, and it made possible the manufacture of glass types which could not be made in the clay pots previously available. The large-scale manufacture of industrial glass took a step forward when the pot was replaced by the tank, with its more favorable type of construction and smaller proportionate surface exposed to the corrosive action of the glass, and the tank has practically displaced the pot in all but the small-scale operations. But the demand for better refractories still is insistent, and has led in the past few years to more intensive study of the alumina-silica refractories. Here the scientific and technical developments have proceeded simultaneously, and it appears probable that in the mullite refractories we have achieved a n improvement of the first magnitude. The same group of refractories is well fitted to withstand high temperatures, and so will doubtless prove of benefit to other industries as well,
915
Advances in Glass Technology
The researches of Schott, and the progressive policy of the glass plant of Schott and Genossen in Jena, resulted in tremendous strides in glass technology in the last quarter of the nineteenth century, and gave the application of science to the industry an impetus which lasted well into the twentieth century. That impetus was apparently waning, however, and a t the outhreak of the European war the glass industry had apparently settled down into well-worn ruts. Under the pressure of necessity glass technology experienced a new awakening, which is now manifest in all of its branches. There are many signs that we are a t the dawn of a new era in our knowledge of glass, its properties and its constitution, which will surely result in improved glass compositions, improved methods of manufacture, and improved methods of treatment; for that has been the invariable and inevitable result of the application of the scientific method to technology.
Fifty Years of Gas Chemistry' By W. H. Fulweiler THE U. G . I. CONTRACTING Co., PHILADELPHIA, PA.
IFTY years ago the gas industry was devoted almost exclusively to illumination. There were a few rather crude stoves used for domestic cooking. Electricity had not appeared as a competitor and state commissions were still unknown. The illuminating value was the standard of quality and but little attempt was made to sell gas as a commodity. Since then there has been an almost complete revolution in the industry. Today probably less than onethird of the gas is used for illumination, the greater portion being used as a most convenient and efficient, source of heat in the home and for thousands of manufacturing operations. The illuminating value has disappeared as a standard of quality and has been replaced by the heating value, a change which started in Wisconsin in 1908. I n nearly all our states regulations concerning quality, service, and rates are under the supervision of state commissions. and practically every company has its new business department endeavoring to extend the use and to increase the sale of gas. The sale of gas per capita in the United States has increased about four times faster than the population, while the average price has been reduced from about $2.30 per thousand to a little over $1.00 per thousand and the average standard of quality has been changed from 16 candlepower coal gas to a 550 B. t. u. mixed gas. Sl'here formerly the companies in our various cities were individual organizations, today many of them are linked together by holding companies, with a resulting increase in the efficiency of management and operation.
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Manufacture of Gas
Practically all the gas was formerly produced by the carbonization of coal, as carbureted water gas was just being introduced, while today this condition is reversed and the greater proportion is carbureted water gas, which is sold either alone or mixed with coal gas. I n the manufacture of coal gas the general trend of development has been towards the carbonization of coal in larger units and to a reduction in the labor required to effect this carbonization. Where coal gas was formerly made in 1
Received July 27, 1926
9-foot horizontal retorts holding 300 to 400 pounds of coal we have today coke ovens holding 10 tons per charge. Practically all the operations of handling the coal, charging i t into the retorts, and removing, sizing, and storing the coke are performed mechanically. The small individual producers for heating the retorts have given way to the large external producer serving a whole battery of retorts. The sensible heat that was formerly wasted in the products of combustion is now recovered in the waste-heat boiler and the hot coke is cooled in apparatus which permits recovering the heat as steam and produces a better quality of coke. Water Gas
The period under discussion has practically furnished the history of the development of the manufacture of carbureted water gas. With the exception of the Lowe process, the earlier processes have disappeared, and our modern carbureted water-gas apparatus has been developed to a very high degree of efficiency. The apparatus is operated by an automatic device, the steam and air are accurately measured, and the temperature is automatically controlled. The self-clinkering grate is just emerging from the development stage, and waste-heat boilers will furnish steam sufficient to operate the process from the sensible heat in the off-going gases. Bituminous coal can be used as fuel with the Pier process and heavy coke-bearing oils can be used in the checkerless carburetor, so that the high capacity and great flexibility of the process, low labor cost, and relatively abundant supply of enriching oil have all aided to make the manufacture of carbureted water gas the most generally used process. The development of the all-oil water-gas process as used on the Pacific coast has taken place during the period under discussion. This process, however, does not appear to be economical under the conditions prevailing a t present on the eastern seaboard. We cannot mention all the changes that have taken place in the condensing and purifying processes, but we can point out that with the change to the heating-value standard more
