Classic Kit: Dewar's flask
Sir James Dewar
© MARY EVANS PICTURE LIBRARY
Yet the first 'double-glazier' was a remarkable man, one to be revered rather than scorned. James Dewar, a Scot, was born in Kincardine-on-Forth in 1842. Growing up in colder times than we know today, he fell through the ice while skating. Confined to bed for almost two years, he learned to build violins, an activity to which he would later attribute his astonishing manipulative skills.
After university at Edinburgh, Dewar spent 16 years in Scotland, working variously as an assistant for scientist and parliamentarian Lyon Playfair, and subsequently for Crum Brown - who was amongst the first to draw molecules using circles and sticks. His work ranged from working (unsuccessfully) on structures of benzene, measuring the temperature of the sun and the action of light on the retina of animals, to determining the structure of pyridine and carrying out simple chemical analyses.
After two years of Cambridge unhappiness, Dewar accepted the post of Fullerian Professor at the Royal Institution in London. Where he had hated teaching to a syllabus, he now enjoyed the freedom of picking and choosing interesting topics for evening discourses. He was a brilliant lecturer.
In 1878 when Raoul Pictet and Louis-Paul Cailletet liquefied air, Dewar saw an exciting research opportunity - the search for absolute zero. He repeated the experiments in public and then pioneered the use of the Joule-Thompson effect - where the temperature of a gas drops as it expands - to reach ever lower temperatures. And his new double-glazed vacuum flasks - now made of layers of silvered glass, with the empty space between them evacuated using Sprengel pumps and cold charcoal - came into their own. But, missing a spectacular commercial opportunity, Dewar never patented the design. In 1904, when a German glassblower discovered that his baby's milk stayed warm for hours in one of the flasks, he began selling them under the name Thermos. Dewar, tetchy at the best of times, was furious, and sued, unsuccessfully, for damages.
In 1895, Dewar showed that, pre-cooled to -200°C and compressed to 200 atmospheres, hydrogen became liquid when squirted through a fine nozzle. Soon Dewar was making liquid hydrogen by the litre. The extreme nature of the work resulted in two of Dewar's coworkers each losing an eye in explosions while conducting the experiments. A painting depicting Dewar holding a flask of liquid hydrogen in the Royal Institution's packed theatre is all the more remarkable when one considers that the room was lit by gas mantles.
More, perhaps, than any other piece of kit in our labs, the mirrored dome of an upturned Dewar flask is a thing of rare beauty, which every chemist should have on the mantlepiece. And so, perhaps, should every double glazing salesman.
Andrea Sella is a lecturer in inorganic chemistry at University College London