ALEXANDER SILVERMAN
University of Pittsburgh, Pittsburgh, Penna.
with modernized wicks. And speaking of LASS had its beginnings in ancient A symposium presented bewicks, a new non-burning variety is made timcs, and history seems too young fore the Division of Industrial accurately to record its first proand Enginccring Chemistry of fiber glass. Gas supplanted oil and, at the 100th Meeting of the with the coming of the Welsbach mantle, duction. Findings of the archeologists go back five thousand years, but the proAmerican Chemical Society, the chimney was modified. Then a carDetroit, Mich. bon filament was enclosed in a vacuum duction of glass was already in so adbulb and electricity played a part. The vanced a stage that the art is probably arc lamp lighted the streets. The tungmuch older. As was aptly stated in an sten filament made its appearance. Science pronounced after-dinner talk recently, glassmaking is a product of its durability dependent upon the gas content of the bulb civilization, for while pottery and other arts go back to and the composition of the bulb. Improved glasses appeared, primitive man, $assmaking has never been an occupation now no longer blown by hand or even in the old bulb of any but a civilized group. machine, but from a continuous ribbon with lenslike elevaDesignating something as old or new is relative. The tions which blow heads convert to bulbs. Already the bulb term “new” in this symposium will refer largely to the prodgives way to the tube, and fluorescent lighting becomes ucts of the present century. For example, beads go back popular. The composition of the glass will determine the to ancient times and glass marbles have been known for nature of the light which is transmitted; the fluorescent centuries, but the production of beads for highway signs ilconting is not the only factor. luminated by reflected light is novel, and the making of The Behistun rock of the time of Darius, 516 B.c., owes marbles to ensure uniformity in cullet in the melting of glass for the production of fibers is certainly new. The fibers the preservation of its inscribed surface to a glaze, for the themselves go back to the Elizabethian period when they were rock layers underneath are eroded. Whether this was a salt glaze or an application of water glass is difficult to determine, spun for aigrettes for the ladies and curls for barristers, but their mass production by steam injection against a flowing but the latter is used for fireproofing of fabrics and in many other ways. Improvements in its method of manufacture, stream of glass to yield wool for thermal insulation, ribbon for electrical insulation, cloth for filtration, etc., is modern. studies of its durability, and widening applications ensure a twentieth century industry. Colored fibers in a r t windows constitute a new application. The use of cloth in various ways in the houschold and for Panes of glass were cast for the baths in Pompeii, but plate apparel has been announced. The naming of a fiber standard, glass did not make its appearance as a rolled product until 1G88 in France. The modern contributions in this field inthe “itchibell”, which is a filament 0.0003 inch or more in diameter, implies that precautions are taken against fibers clude the casting from very large pots and the shearing of the which would be too coarse in cloth used for apparel, and wllich casting into two plates, RS well as the continuous flowing of glass between rolls. Plate is polished to ensure a smooth and might produce a dermatitis. level surface, but until recently comparatively little attention Early Egyptian flasks at times almost assumed the shape of an Erlenmeyer, but the real advent of chemical glassware was given to the measurement of surface irregularities. D e vices are now employed for inspection which will record a follows tho coming of Otto Schott to Jena, Germany, about 1880; and the high borosilicate glasses made their only vertical magnification of 5000 and a horizontal of 450. Minute appearance after the first World War. Now comes the anirregularities are magnified to a point where they are easily nouncement of the brand new “Vycor” glass in which a partly perceptible in records. Polishing meters indicate total reflecsoluble blank is treated chemically nnd the skeleton re-fused tion from the surface and permit the evaluation of polishing to yield a glass 30 per cent smaller which contains over 06 per materials and methods. ccnt silica. Its coefficient of thermal expansion is only about Plate is made in black, white, and a variety of other colors one third that of the best chemical laboratory ware formerly for store fronts, corridors, and other building construction. produced. Quartz fibers have long served as a suspension in Inlaid plate, from cutouts set into suitable openings, and galvanometers, but the making of transparent fused quartz relief designs set on plates provide advertising signs and art in vacuum-pressure electric furnaces is a modern accomplishpanels. ment. The more crude fused quartz, which is employed in The Prince Rupert drop was a curiosity in the laboratory the laboratory and in industry, is comparatively modern. long ago, and students delighted in exploding the casehardened glass pellets. The tempering of large surfaces is new and is MOSQUE lamps and others for the home contained a burning an enormous step from a Labasti chimney to a large plate wick in animal or vegetable fats until the dicovery of keroglass pane. Oil chilling of the hot glass has given way to sene, when the lamp chimney afforded better illumination controlled air chilling. In limited cases fused salts are em-
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ployed. It is now claimed that the surface hardening can be so controlled that specially treated glass will not shatter through superficial scratching. Normally, a scratch results in crumbling to innumerable fragments.
THE lamination of plate glass dates back to the oft-told story of the French professor and the broken flask which had been lined with a dried collodion lilm. The newer plastics, which ensure clarity, flexibility, and freedom from gas accumulation in the interlayer, write their own history. A patent was issued recently for a plate of glass which contains a plastic layer on one surface so that, in the crashing of a windshield, glass fragments will be entirely on the side farthest from the occupants of the car. When the surface hardness of plastics becomes sufficiently great, they may even compete with glass. Petitjean’s wet silvering process of 1855 has undergone little change in principle. The separate spraying of the silvering and reducing solutions is novel. Limiting the thickness of the silver film has yielded transparent mirrors. Applying aluminum i n vacuo from electrically heated troughs furnishes a reflector rich in all parts of the visible spectrum, especially the violet; besides, the mirror is on the near side and independent of glass color. Another new development with plate glass involves spraying the hot surface through a stencil with a continuous aluminum pattern whose resistance to the flow of current permits the use of decorative electric heaters. It is possible to carry the principle farther by having plate glass floors which are heated electrically. It is claimed that if floors are warm, a lower than normal room temperature affords comfort. Theophilus, an Anglosaxon monk of the twelfth century, gave us the hand-blown window glass cylinder which was elaborated into a mechanical process by Lubbers late in the
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have resulted in a product which approximates plate glass in perfection. It is even possible to laminate the finer window glass. The Fourcault machine, combining two or more colors drawn from separate melting tanks, produces cased or multilayer sheet glass of unbelievable regularity. Some of the color layers-opal or gold ruby, for example-are so thin in cross section as hardly to be visible to the unaided eye. Bottles possess an endless variety from early Egyptian days to the present. Their manufacture beyond a million per day results from machines which surpass human capacity. A scientific study of composition affords containers in which the color of food is stable and in which medicinals are unaffected. Quantity and special quality are new. The drinking glass was the privilege of the wealthy in ancient times. A better article is a mere container of a food product today. With its melted or bead edge to prevent chipping, and in some instances tempering to caseharden the tumbler, modern tableware possesses a stability beyond the dreams of the past.
I N THE optical field the addition of some twenty-five elements and their compounds, by Schott and Abbe, to the pre-existing five of 1880 was notable. The large cast reflectors of the latter nineteenth century aroused the admiration of astronomers, but the 200-inch reflector of Corning will eclipse all past efforts, if i t continues successfully to progress in its preparation. Changes in composition of optical glasses in some cases raise the index of refraction and in others control refringence for better recording of color. Optical details will be presented later. The recent application by Cartwright and others of chemically produced surface films to lower reflection in flat sheet and lens systems has increased transmitting efficiency
INLAID GLASS MUR;AL
Courtcey, Pithburoh Plate ofass Company
nineteenth century. This has given way in the twentieth century t o direct sheet processes, vertical by Fourcault of Belgium and horizontal by Colburn of Pennsylvania. Numero w modifications are incorporated in the patent literature. The world no longer splits and flattens cylinders. Improved equipment and control of physical properties of the glass
in an almost startling way. As Cartwright himself has commented, “It makes one wonder whether cleanliness is next to Godliness for light transmission.” Other new developments in optical glasses cover absorption and transmission of special radiations. The lithium-beryllium borates with their x-ray transparency and the high-lead
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Couriaay, Li/e Mogorine
C . HAWLEY CARTWRIOHT, OF MABSACHUSETTS INSTITUTE OF TECRNOLOOY, Pnomuanpmn (left) WITE AN U N T R E A ~ D LENSAND (right) THROUCH A LENSTREATED WITH HIS MAQNESIUM FLUORIDB FILM PROCESS
uranium glasses with x-ray opacity serve in x-ray studies and protection of operators, respectively. Then there are the new glasses which are transparent to ultraviolet, from pure quartz through the phosphates, and others which ahsorh the ultraviolet, such as the cerium glasses. Again, there are the glasses which are opaque to visible light hut transmit ultraviolet, the dark nickel-cobalt compositions which house lights for fluorescence studies in either mercury-vapor or filament lamps. Heat absorption has our attention. Special glasses containing the ferrous ion ahsorh to such an extent that a radiometer placed beyond them comes to rest. Eye-protective lenses to eliminate glare are not particularly neu’, hut Iaminated glass containing Polaroid, an oriented distribution of quinine iodosulfate crystals in a film, producesaneye-satisfying polarizer-analyzer effect. In time this method of light treatment will generally eliminate highway glare for the driver and will bring three-dimensional pictures to the motion picture theater. ILLUMINATING glassware is subject to specifications both varied and exacting. For some purposes light transmission is demanded, for others high reflection. The versatility of manufacturers and technologists in meeting this wide range from translucency to opacity is encouraging. Color tone plays a part, and tints practically cover the pastels of the palette. The modern torchhe, with its direct-indirect or entirely indirect light sets an even wider color flexibility reouirement for elass. The fluorescent tube lamn creates new problems. Highway, theater, and other special lighting have made demands. Sodium-vapor lamps required a new glass of a comDosition which would resist the action of the metal vaDor. The-sealed-in automobile headlight or spotlight brought its particular requirements; and while the thousand-watt cigaret lamp, so-called because of its size, is a reality, the highmelting glass which incases the illuminating unit is still capable of further improvement.
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Lighting means more today than mere efficiency. The artistic plays an everincreasing part. It is no exaggeration to say that one can enjoy anything from sunrise to moonlight, assuming that he can finance the necessary installation and controls. With air conditioning and the possibility of climatic control, the home can respond to every mood. Many lighting units and signal lenses are pressed. While this is not new, the heat treatment of huge heavy howls up to 24 or even 30 inches in diameter is a problem which has required new procedure. Among the products of the glass press, blocks used for making building tile are new items. The methods of combination by dipping edges into molten aluminum or welding the edges or sticking them together in special ways are new. Internal treatment as to design or metal coatings must he mentioned. Perhaps curved pressed roofing tile and reinforced shingles should he included. Buhhle glass has made its appearance in several forms. This is not the glass in which bubbles are introduced for decorative effects, hut a cellular glass formed either by mixing glass powder with a vaporizable substance in molds or by subjecting a pulverized, incompletely melted glass composition to a vacuum under heat. The new cellular glass, ranging from a dull gray stonelie color to white with colored enamel surfaces, is a valuahle insulating material. Though not as strong as plate glass, i t can be used for surfaces while glass wool would have to he protected. It possesses the advantage that there is no moisture condensation as in glass wool. Both types of insulation are vermin- and rodent-proof and are nonflammable. CHEMICAL composition has been referred to repeatedly. In the colorless transparent glasses, modifications have come about which are too numerous to list here. A study of selenium ruby effectshas resulted in an understanding of the color composition, with the consequence that i t could be prepared in advance and redden the glass directly instead of hy heat treatment. Copper ruby has been revived through the
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use of sodium cyanide which also yields direct color. Ceriumtitanium yellows possess an unusual charm. The neodymium wisteria with its attractive dichroism is a commodity. Opal glasses of varied density and opacity have come through composition studies and control of heat treatment. The elements calcium, lead, and silicon in the opal glasses have found zinc and aluminum and boron compatible; the new alabasters are less susceptible to oxidizing-reducing influences than the old opals and alabasters. The new translucence is attractive and effective. Much has been learned regarding the influences of oxidation and reduction. The relative oxidizingreducing powers of compounds have located them in their proper places in a series of such agents. The addition of volatilizing agents to the batch to remove substances which produce color has lessened color through contamination and lowered decolorizer requirements. Natural raw materials have been given chemical baths or vapor treatments for purification. The traditional silica loss through fluorides in glass melting is now only half a tradition, for the loss depends largely on moisture. Calcined borax, pearl ash, alumina, and other glass chemicals ensure controlled reactions. Natural nitrates were displaced by those resulting from fixation processes. Glass color was affected differently. It was found that the iodine compounds of the natural nitrates were missing. Iodides were added to the batch. Titania, once a small corrective factor in silica determinations, has become a commodity and is bought by the ton for plate glass. The classical concepts regarding the influence of boron, magnesium, and other elements on thermal expansion were modified. It was found that the effects depended upon the proportions used and differed appreciably according to concentration. The general fixed notion of additive tendencies is no longer tenable. It applied to limited regions. This introduction merely hints a t chemical and physical effect*. More will follow later. What is the composition of glass? Chemical analysis reveals only the percentage composition. Thermal analysis through cooling curves has hinted at compounds. X-ray studies of silicates and other minerals related to glass hint a t possible compounds in glass. When crystallites form i n
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the glass and a component is present in sufficient quantity, a photogram reveals its nature. The old stoichiometric calculations which are based on equivalent weights give way to chemical substitution-proportions prompted by a lattice picture. How one element replaces another, the lattice may also indicate. Structural studies are taken up a t greater length later.
FURNACES and refractories, while they deserve a separate discussion, must a t least be mentioned. Furnace design to suit special needs has undergone endless modification. With new compositions, new melting and working temperatures are required. For these, small melting units have served better than multiple pot furnaces. Reactions between chemicals and refractories have prompted composition changes for batch and refractory. It is not surprising to find experiments going on with the refractory limits pure sandstone on the one hand, and electric furnace alumina on the other. The glassmaker is handicapped through having to exclude refractories which impart color to glass. Finally, a few words about art. It no longer suffices to have an artist devote himself to the production of the unique and the exclusive. The new contributions by Swedish artists of interlayer designs in heavy vases and the control of bubble decorations which make the bubble slave to the artist in size and shape, possess unusual merit. The accomplishments are daring but costly. The use of colored fiber glass for art windows is novel and the windows are most attractive. The artists in the Vatican studios in Rome have over 50,000 mineral color tones in glass available for their mosaics. But, it is the art for every man that counts. This has come through the silk screen and the applied enamel. It has come through the designer and the press mold. Commercial a r t is a twentieth century gift. Floodlights have illuminated the picture, “What is old? What is new?” Spotlights will now carry us in turn to the more special considerations, chemical trends, physical tendencies, optical characteristics, and structure. CONTRIBUTION401 from the Department of Chemidry, University of Pittsburgh.
