They fill the container with pure air made by evaporating liquid nitrogen and liquid oxygen, and add water vapour and some trace gases.

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By footling round with centrifuges and liquid nitrogen they were reducing food to a set of mental hurdles, as though there weren't already enough traffic lights and zebra crossings in life.

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The helium, which by then will have risen to about minus 15C, is pushed through a liquid nitrogen "boiler" to bring it back down to its run temperature, before looping back into the pre-cooler.

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