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Ever hot The 1950s Thermal Teapot. Snippet Of The Day Number 4

Ever hot The 1950s Thermal Teapot.

Ever hot The 1950s Thermal Teapot. Snippet Of The Day Number 4

Do you know how a ‘Thermos’ flask keeps your tea warm, or any thermal mug or flask for that matter? Well, this remarkable ‘ever hot’ phenomenon is based on the principle of the vacuum flask invented by James Dewar in 1892! A very simple design, which basically comprises a sealed double walled container, made of e.g. glass or metal, with a partial vacuum between each layer. As shown in the schematic below.

Ever hot The 1950s Thermal Teapot.
Vacuum Flask. Double wall insulating container sealed at the neck, with a partial vacuum between the two layers.

The presence of the vacuum slows down the heat transfer by conduction and convection from the inner container. Rate of heat loss can be assessed thermodynamically but that is a bit more complicated and definitely outside the scope of this blog!

Dewar decided not to patent or copyright his invention, which was soon improved, superseded and copyrighted by the German company ‘Thermos’. Hence, you are more likely to hear vacuum flasks called ‘Thermos,’ in a domestic setting.  In  Science Laboratories and in industrial settings, they are often still referred to as ‘Dewar flasks.’

Ever hot The 1950s Thermal Teapot by Perry, Bevan and Co

Most tea drinkers know about the problems of lukewarm tea when making a ‘proper’ cup of tea in a teapot. You warm your pot with boiling water and then brew your tea for at least three minutes. In that three minutes your tea can lose an awful lot of heat due to heat loss from the teapot itself. If you want a second cup from the pot you had to find a way of reducing the heat loss.

Until late Victorian times, this was achieved via the tea cosy. {The designs and shapes of this very useful household item deserves a blog in its own right! I have fond memories of my Grandmother knitting or crocheting a tea cosy to fit the 2-cup, 4-cup and 8-cup Brown Betty teapots she owned.}  This was until the 1950s when Perry, Bevan & Co. patented the Ever-Hot tea service. At the time, Ever hot The 1950s Thermal Teapot was a very innovative design negating the need for the lovely knitted or crocheted tea cosy!

This is a contemporary advert for the patented Ever-Hot tea service by Perry, Bevan and Co. They were based at 133 Priory Road, Aston, Birmingham. The company was listed as Brass Founders in the 1940s, in addition to manufacturers of Chrome ware.

ever-hot-advert-tiff

The earthenware teapot comprises a felt-lined chrome plated insulating casing, with a built-in lid. This doesn’t create a vacuum in the same way as a thermos/ dewar flask, but does provide some insulation with its two layers. Some teapots also had a separate tea strainer, that sat inside the pot, so that you could add the tea leaves directly to the pot. The felt could be removed and washed too! Needless to say that this design was also superseded by the arrival of more modern manufacturing methods and materials.

1950s Vintage Everhot Tall Teapot, Milk Jug, Sugar Bowl
1950s Vintage Everhot Tall Teapot, Milk Jug, Sugar Bowl

 

 

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