16 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS One of the early definitions of glass was given by Christopher Merrett in 1662 in connection with his translation from the Italian of Antonio Neri's L'arte Fetraria ("The Art of Glass"). "Glass is one of the fruits of the fire, which is most true, for it is a thing wholly of art, not of nature, and not to be produced without strong fires. I have heard singular artists merrily to this purpose say, that their profession would be the last in the world, for when God should consume with fire the universe, that then all things would vitrifie and turn to glass." The definition continues to occupy a whole page of text, including twenty- six clauses, of which the twenty-fourth might be considered to be of special interest to chemists: "Brne, beer nor other liquors will (not) make them musty, nor change their colour, nor rust them." Glass does of course appear in nature, though not, as Merrett said, without the agency of "strong fires". It has been used by man from the earliest times of which we have archaeological record and objects shaped by hand from natural glasses by primitive people, have been found in widely separated localities. These natural glasses represent molten rock masses which were extruded and cooled so rapidly that they did not have time to become transformed into the usual aggregate of crystalline materials. The commonest of these glasses, obsidian, is usually translucent and blackish in colour, but is sometimes red, brown and greenish, and some varieties are transparent. It is easily broken into sharp, often elongated pieces, which lend themselves readily to the fashioning of spears, arrowheads and knives, and its use for such purposes by people of Stone Age culture was widespread. In more advanced cultures, obsidian was valued also for ceremonial purposes and for jewe!lery, some of the articles made from it showing a high quality of handicraft. Apart from the natural glasses of igneous origin, there is another group comprising mainly fulgurites and tektites. Fulgurites are formed by light- ning striking sand, or other loose porous materials. Until Franklin discovered the true explanation of lightning, a fulgurite was commonly supposed to be the remains of the lightning bolt. An example found in a sandpit, in the United States in 1925, consisted of 99% silica, the fragments recovered representing a total length of nine feet, with a maximum diameter of three inches tapering to three-sixteenths of an inch. Tektites is the name given to a group of glasses found in many parts of the world, usually considered to be of meteoric origin. An early hypothesis to explain their formation, discredited for some years but recently revived as the result of further investigations, was that they were volcanic bombs shot from the moon during the Pleistocene periods. Other workers have suggested that tektites may be aerial fulgurites, resulting from the fusion by lightning of dust in the

PRODUCTION AND PROPERTIES OF GLASS CONTAINERS 17 air, while another possibility is that they are formed by the impact of meteors on sand or sandstone, producing a pool of molten material which is shaped by splashing for a great distance through the air. Lumps of silica glass have been found in the Libyan desert, formed apparently by this method. The agency of lightning, apart from producing the fulgurites, may in fact be a possible origin of the commercial manufacture of glass. A French writer in 1878 first drew attention to the not uncommon occurrence of the burning of grain and fusion of the ash as the result of fire caused by lightning. The masses of glass found in the ash were called "lightning stones" (pierres de foudre) by the French peasants, who believed them to be the cause of the fire. For many centuries, plant ash of various types was one of the major constituents of glass making batches and the anhydrous sodium carbonate used by glass manufacturers today is always referred to as soda ash. Another illustration of the possible accidental origin of glass manufacture was related by Pliny in his "Natural History" in the first century A.D. He refers to the banks of glass making sand which were situated at the mouth of the River Belus in Phoenicia and which at that time had been in use for many years. "The story is that a ship, laden with nitre (i.e., sodium carbonate), being moored upon this spot, the merchants, while preparing their repast upon the seashore, finding no stones at hand for supporting their cauldrons, employed for the purpose lumps of nitre which they had taken from the vessel. Upon its being subjected to the action of the fire, in combi- nation with the sand of the seashore, they beheld transparent streams flowing forth of a liquid hitherto unknown this, it was said, was the origin of glass.'• This story is a plausible one, though it has been doubted if sufficient heat could be developed by an open fire as described. An American investigator has found that a wood fire kept burning for two hours in the open developed a temperature of 1200øC, which would be sufficient to melt not only a soda- silica glass but also a soft soda-lime-silica glass. (The lowest-melting eutectics being respectively at 793øC and 725øC.) The discovery of glass manufacture could have been made in the way related by Pliny, but the dating of the oldest piece of glass indicates that it took place hundreds of years before the time of the Phoenician traders. Where and when glass manufacture had its beginning is an open question, but the oldest piece of glass actually bearing a date, now in the Ashmolean Museum, Oxford, was made between 1,551 and 1,527 B.C.E. Some authorities have given dates as early as 12,000 B.C.E. for glazes, and 7,000 B.½.•. for pure glass, though the difficulty arises of establishing whether many of the early pieces are glass at all and not natural stones. As regards written records, a chemical text of Babylonian origin of 1,700 B.C.F•. or earlier, contains recipes for four glazes based on a "master glass", unfortunately unspecified, while the "Nineveh