The men wore evening dress complete with white tie and upturned collar. The ladies wore silk gowns and fur wraps. Although it was a chilly January evening, the whole of London society seemed to be heading for the Royal Institution. Why? Because tonight James Dewar was going to show off the strange properties of liquid gas.
The place was packed. As Dewar began to pour a little liquid air into a beaker of water, the audience leaned forward. There was a violent bubbling. And as the air boiled it swept up tiny drops of water vapour, creating clouds of white fog that enveloped Dewar almost completely. But for one person, Dewar鈥檚 vanishing trick was just a distraction. Agnes Marshall was more excited by what was going on in the beaker. As the air boiled off, the water left in the beaker turned to ice. Mrs Marshall was the most famous cook of her day, renowned especially for her ices and sorbets. Dewar had just shown her a way to make instant ice cream.
IN 1894, when London鈥檚 fashionable folk were flocking to the Royal Institution for an evening鈥檚 entertainment, James Dewar was a celebrity-a chemist who could hold an audience spellbound with little more than a few flasks and a theatrical flourish. Agnes Marshall, proprietor of Mrs Marshall鈥檚 Cookery School, half a dozen streets from the Royal Institution, was equally famous. She was the original celebrity chef and her culinary triumphs generated as many column inches in the newspapers as Dewar鈥檚 scientific ones. Her lecture tours drew audiences every bit as large as his. And there was something else they had in common: an enthusiasm for low-temperature chemistry.
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Dewar鈥檚 interest was purely scientific. By the time he took up his post at the Royal Institution in 1877 he was busy investigating how the properties of materials changed at low temperatures. To pursue this line of inquiry, he had to achieve extremely low temperatures-which meant he needed liquid nitrogen. That year, Swiss scientists made a few drops of liquid air. It took another 10 years for a pair of Polish chemists to fill an egg cup with liquid nitrogen-and then it vanished in minutes. But they had shown it was possible to liquefy gases.
In London, Dewar experimented doggedly, trying to find a way to make larger amounts of liquid gas. By 1894 he had built a machine that could produce several litres of liquid nitrogen or oxygen a day. He had also invented the vacuum flask which allowed him to store the liquid gas long enough to perform his experiments. He was ready to amaze the public.
鈥淔rom floor to ceiling the building was densely packed with visitors,鈥� reported the Daily Chronicle on 20 January. Piled upon the lecture table was a perfect forest of apparatus, and punctually at 9 o鈥檆lock the laboratory assistants bore in many flagons of that precious fluid, liquid air, of which so much has been heard of late.鈥�
Mrs Marshall鈥檚 interest in low temperatures was more down to earth. Agnes was the Queen of Ices. Her Book of Ices published in 1885 was a bestseller. Not surprisingly, she was keen to find a way to speed up the transformation of warm eggs, cream and sugar to ice cream.
The biggest problem in making ice cream had always been in cooling the mixture. In the three centuries since the first ices appeared on an English table, the technique hadn鈥檛 changed. A pewter bowl of ice cream mixture was lowered into a bucket of salted ice, which brought the temperature down to around -14 掳C-low enough to freeze the contents of the bowl. Until Victorian times, however, ice was so scarce that ice cream was a luxury only the wealthy could afford. The very rich had their own insulated icehouses to store ice collected in winter from frozen ponds and lakes.
In the mid-19th century ice cream became a treat almost everyone could enjoy. The influx of Italian immigrants, including skilled ice cream makers, fuelled the demand for ice. Hundreds of tonnes were shipped to England each week from Norway, where ice was 鈥渇armed鈥� from lakes and glaciers. The ice was taken by barge to storage pits, ready for sale to fishmongers, hospitals and ice cream sellers. Soon anyone could buy ice whenever they wanted from ice men who carted huge blocks around the city streets and chipped off pieces to order.
The other boon for housewives who wanted to make their own ices was the hand-cranked machine invented in 1843 by American, Nancy Johnson. This was simply a container set in a wooden bucket and fitted with a paddle and a handle. All you had to do was put your ice cream mixture in the inner tin and fill the gap between tin and bucket with crushed ice and salt. When you turned the handle, the paddle scraped the mixture from the walls of the tin, ensuring even freezing. It took around 20 minutes to make a good helping of ice cream.
Mrs Marshall was always looking for better ways of doing things. She quickly adopted new kitchen gadgets-and invented some of her own. She improved on Johnson鈥檚 ice cream machine with her own patent freezer. This was more of a flat pan than a bucket and reduced freezing time to three minutes. To keep the product from melting, she came up with the 鈥渋ce cave鈥�, a forerunner of the refrigerator cooled by an outer sleeve filled with ice and salt. Her other great invention was the ice cream cone. In her Book of Cookery, published in 1888, she describes how to make cornets filled with ice cream-16 years before they were 鈥渙fficially鈥� invented at the St Louis World鈥檚 Fair.
No one knows if Mrs Marshall was in the audience when Dewar first showed off his liquid air. But she certainly knew all about his ultra-cold fluids. When she saw-or read about-Dewar鈥檚 cloud-conjuring trick her thoughts sprang immediately to the dinner table. Here, she realised, was a way of making instant ice cream. By 1901, Mrs Marshall was extolling the virtues of liquid air in her magazine The Table.
鈥淟iquid air will do wonderful things,鈥� she wrote. 鈥淏ut as a table adjunct its powers are astonishing, and persons scientifically inclined may perhaps like to amuse and instruct their friends as well as feed them when they invite them to the house. . . Each guest at a dinner party may make his or her ice cream at the table by simply stirring with a spoon the ingredients of ice cream to which a few drops of liquid air has been added by the servant.鈥�
Further reading: Mrs Marshall: The Greatest Victorian Ice Cream Maker by Robin Weir and others (Smith Settle, 1998)