The main purpose of the last paragraph is to demon- strate that the: part of the author’s writing. often change. west, the harder it is for him to write about it. someday despite having been away for so long. 31 GO ON TO THE NEXT PAGE. ACT-G19 3 3 www.actexam.net www.crackab.com Passage II SOCIAL SCIENCE: This passage is from the book Periodic Tales: A Cultural History of the Elements, from Arsenic to Zinc by Hugh Aldersey-Williams. The breakthrough that enabled gas to maintain its advantage over the newfangled electric lighting for a little longer during the closing years of the nineteenth century was made by Carl Auer, later the Baron von Welsbach, a Viennese who had completed his studies in Heidelberg with Robert Bunsen, long the guru of Euro- pean chemists. On his arrival in Heidelberg in 1880, Auer showed the great man a modest collection of rare earth mineral specimens that he had amassed, and Bunsen set him to work analyzing them, laughing off Auer’s protests that the quantities were insufficient. This project set the course of his career; and the rare earths would make his fortune. Auer’s annus mirabilis came in 1885 back in Vienna, when he succeeded in separating the supposed element didymium into two true elements, which were duly named praseodymium and neodymium. Their green and pink compounds make them attractive for use in ceramic wares and in tinted glass for protective eyewear. Auer was not content merely to add to the number of the rare earths. In his Heidelberg days, he had mar- veled at Bunsen’s already famous burner, with its tun- able flame that could be adjusted to simmer or roast. He had noticed how, when turned up high, the Bunsen burner flame would cause his rare earth ores to glow brightly with their own light. He began to explore this phenomenon with different combinations of metal oxides. It was well known that a flame set against a piece of lime (calcium oxide) will produce the incan- descence known as limelight. Auer’s investigation included the oxides of magnesium and beryllium, both closely related to lime, as well as those of his rare earths and other elements. Gas lighting was well established in streets and homes by the mid nineteenth century, but the light it shed was limited by the luminosity of the flame it pro- duced, which depended in turn on the mixture of hydro- carbons being burnt. Candles and oil lamps gave a brighter light than gas, but only gas could be supplied continuously. Auer believed that a lamp design in which his rare earth oxides were positioned close to the gas flame might yield a brighter light. Over a period of several years, he soaked sleeves of cotton mesh in dif- ferent mixtures of rare earth and other salts. Once dried, these sleeves or mantles, now stiff with encrusted oxide, were placed around the flame, which burnt away the fabric to leave a brittle lace of the refractory oxide. This would then glow brightly in the heat of the flame. Little was known about the properties of many of the oxides, and still less about how they behaved in combination, so there was no way of predicting which composition would produce a white incandescence. Auer first patented a gas light with a mantle made of a mixture of magnesium, lanthanum and yttrium oxides in 1885, but its fragility and sickly green light meant that it remained unpopular. However, by 1891, he found that thorium and cerium oxides mixed in the propor- tions of ninety-nine to one gave a satisfactory white light (thorium is not a rare earth but is the heavier— and, unknown then, radioactive—cousin of cerium). Mantles made of this material were more sturdy and quickly caught on. Unusually for a scientist, Auer was an astute businessman, and his name soon became more widely known even than Bunsen’s. For while the bunsen burner had its place in the laboratory, the bright new Auerlicht, as it was known, was of utility to all, and was rapidly distributed across a grateful continent by various Auer companies. Some 90,000 Auer mantles were sold in Vienna and Budapest alone in 1892; twenty years later, annual production stood at 300 mil- lion units. It can have done no harm to the inventor’s prospects that Auer, a variant of the prefix Ur-, is an archaic German word for the dawn. At the exact moment when the first of Auer’s bright gas lamps was lit outside the Opern Café in Vienna on 4 November 1891, Auer’s countryman Gustav Mahler, no stranger to the place, was composing a song that would be incorpo- rated into his second symphony, called ‘Urlicht’—pri- mordial light. Auer clearly acquired a taste for appending his name to his inventions. He followed up the success of the gas mantle with an osmium electric filament, the Auer-Oslight—even as he perfected his gas mantle, Auer was hedging his technological bets by experi- menting with materials for the electric lamps that he already suspected might one day replace them. From pages 366–368 of the book Periodic Tales: A Cultural History of the Elements, from Arsenic to Zinc by Hugh Aldersey-Williams (©2011 by Hugh Aldersey-Williams). First published in 2011 by Viking, an imprint of Penguin Books Ltd, London. Reproduced by permission of Penguin Books Ltd.
