Sep 202013


Today is the birthday (1842) of Sir James Dewar FRS, Scottish chemist and physicist. He is probably best known today for his invention of the Dewar flask, which he used in conjunction with extensive research into the liquefaction of gases. We now know the Dewar flask as the Thermos flask. He was also particularly interested in atomic and molecular spectroscopy, working in these fields for more than 25 years. Dewar’s scientific work covers a wide range of topics: organic chemistry, hydrogen and its physical constants, high temperature research, the temperature of the sun and of the electric spark, electro-photometry, the chemistry of the electric arc, and the properties of liquefied and solidified gases.

With Professor J. G. McKendrick, of Glasgow, he investigated the physiological action of light, and examined the changes which take place in the electrical condition of the retina under its influence. With Professor G. D. Liveing, one of his colleagues at Cambridge University, he began in 1878 a long series of spectroscopic observations, the later of which were devoted to the spectroscopic examination of various gaseous elements separated from atmospheric air by the aid of low temperatures; and he was joined by Professor J. A. Fleming, of University College London, in the investigation of the electrical behavior of substances cooled to very low temperatures.

NPG x5199; Sir James Dewar by (Mary) Olive Edis (Mrs Galsworthy)

His name is most widely known in connection with his work on the liquefaction of the so-called permanent gases and his researches at temperatures approaching absolute zero. His interest in this branch of physics and chemistry dates back at least as far as 1874, when he discussed the “Latent Heat of Liquid Gases” before the British Association. In 1878 he devoted a Friday evening lecture at the Royal Institution to the then recent work of Louis Paul Cailletet and Raoul Pictet, and exhibited for the first time in Great Britain the working of the Cailletet apparatus (for producing droplets of liquid oxygen).


Six years later, again at the Royal Institution, he described the researches of Zygmunt Florenty Wróblewski and Karol Olszewski, and illustrated for the first time in public the liquefaction of oxygen and air. Soon afterwards he built a machine from which the liquefied gas could be drawn off through a valve for use as a cooling agent. About the same time he also obtained oxygen in the solid state.


By 1891 he had designed and built, at the Royal Institution, machinery which yielded liquid oxygen in industrial quantities, and towards the end of that year he showed that both liquid oxygen and liquid ozone are strongly attracted by a magnet. About 1892 the idea occurred to him of using vacuum-jacketed vessels for the storage of liquid gases – the Dewar flask – the invention for which he became most famous. The vacuum flask was so efficient at keeping heat out that it was found possible to preserve the liquids for comparatively long periods, making examination of their physical properties possible. Dewar did not profit from the widespread adoption of his vacuum flask, however. In fact he lost a court case against the Thermos company concerning the patent for his invention. While Dewar was recognized as the inventor, because he did not patent his invention there was no way to stop Thermos from using the design and profiting from it.


He next experimented with a high pressure hydrogen jet by which low temperatures were realized through the Joule–Thomson effect, and the successful results he obtained led him to build at the Royal Institution a large regenerative cooling refrigerating machine. Using this machine in 1898, liquid hydrogen was collected for the first time, solid hydrogen following in 1899. He tried to liquefy the last remaining gas, helium, which condenses into a liquid at ?268.9°C, but owing to a number of factors, including a lack of helium with which to work, Dewar was preceded by Heike Kamerlingh Onnes as the first person to produce liquid helium, in 1908. Onnes would later be awarded the Nobel Prize in Physics for his research into the properties of matter at low temperatures. Dewar was nominated several times but never successful in winning the Nobel Prize.

(c) National Galleries of Scotland; Supplied by The Public Catalogue Foundation

[Image courtesy: National Galleries of Scotland]

In 1905 he began to investigate the gas-absorbing powers of charcoal when cooled to low temperatures, and applied his research to the production of high vacuums, which were useful for further experiments in atomic physics. Dewar would continue his research work into the properties of elements at low temperatures, specifically low-temperature calorimetry, until the outbreak of World War I. The Royal Institution laboratories lost a number of staff to the war effort, both in fighting and scientific roles, and after the war, Dewar had little interest in restarting the serious research work which went on before the War. Shortages of scholars necessarily compounded the problems. His research during and after the war mainly involved investigating surface tension in soap bubbles, rather than further work into the properties of matter at low temperatures.

Dewar died in London in 1923 at the age of 80, still holding the office of Fullerian Professor of Chemistry at the Royal Institution, and still involved in research.

Thermos Cooking

Nowadays with microwaves everywhere the Thermos flask has lost its usefulness to a great extent, although it still has a part to play when out hiking and such.  I don’t recall a time when I have been without a Thermos.  When I was a boy we had one that we carried to picnics and the beach in a beautiful buff leather, cylindrical carrying case with a long shoulder strap.  I think the whole kit came from Argentina from around the time when I was born.  The thermos is an essential part of yerba mate drinking here because you need a constant supply of hot water to refill the gourd as you drink.  Every household has at least one; I have two.  My mum needed ours for family outings because she could not survive without her 4 o’clock cuppa and a biscuit.

Cooking in a Thermos was quite common at one time, particularly in situations where other cooking equipment was limited, such as in battlefield conditions. The principle is very simple.  You place the uncooked ingredients in the Thermos surrounded by boiling water or other liquid, close it up tight, lay it on its side, and let the contained heat do the cooking.  It’s like a crock pot except you do not need an external heat source.  It’s a green resource that could use a comeback.   You just need some basic equipment.  First you need a high quality Thermos that can hold its heat reliably for 12 hours or more (even if you are cooking for a lot less time).  The best will give you 24 hours.  It should be a quart capacity or better in order to make a good amount of food.  You also need a canning funnel to get the boiling ingredients in without dangerous spillage.  You can make soups or pasta within 20 to 30 minutes this way.  You can also make long cooked stews using the toughest meat. These will take overnight, but you put no effort in except at the beginning.  The two cardinal rules are:

1.    Pack the ingredients well and leave as little air space at the top as possible.
2.    Heat the interior of the Thermos well with boiling water prior to doing the cooking so that the actual cooking liquid is not cooled significantly when it is put in the flask.

Here’s a simple recipe for one of my favorite soups – leek and potato – an old English standby. The ingredients are just ratios because you will have to adjust for the size of your flask.  Some people like to blend this soup like a hot vichyssoise, but I prefer it as is — flavored broth with distinct vegetables. The potatoes thicken the base enough for me.  If you want vichyssoise then make vichyssoise.

Leek and Potato Soup

Thermos Leek and Potato Soup


1 part leeks, sliced thin
1 part potato, peeled and diced small
chicken stock


Mix the leek and potato bits together and fill the Thermos with them. Push down gently to be sure they are packed well and add more to fill. Add cold stock to the very top of the thermos. Then empty the entire contents into a saucepan adding a small amount more of stock to be sure you have ample to refill the flask.

Boil a kettle of water, fill the thermos with boiling water and cap tightly.  Meanwhile bring the stock and vegetables to a boil.

Empty out the boiling water from the flask (maybe into a tea pot or drip coffee pot so as not to waste it), and, using a canning funnel, fill the flask with the boiling soup.  Cap tightly and lay the flask on its side.  The soup will be cooked in slightly longer than it takes to simmer it on a stovetop – about 25 minutes for me, longer if you want softer vegetables.