Below X °C/°F or below -X °C/°F?

Question

In a text about fluorine, a sentence reads:

It is stored as a super-cooled liquid (below –200°C/–392°F) in nickel or copper containers, which do not react strongly with fluorine.

While there is a sentence in the Wikipedia page about fluorine that reads:

Fluorine can be stored in steel cylinders that have passivated interiors, at temperatures below 200 °C (392 °F); otherwise nickel can be used.

I was not sure which one is right, so I checked the dictionary. Under the entry "below", one of the definitions is:

under zero on the temperature scale

I also search the Internet a bit, and all examples seem to support the Wikipedia sentence.

However, the Chinese version of the Wiki page clearly states that it means "less than 200°C/392°F".

From all I've searched, I'm quite sure that the English Wiki page is the correct usage, while the Chinese version and the other text are wrong. After all, Wiki pages are not translated by professionals. Also, I know fluorine has to be stored in a very low temperature, which means "less than 200°C/392°F" is just not cold enough.

But I still want to be absolutely sure. So please confirm if I reasoned it right or not. Thank you!

P.S. Also, can I place "below" after the number? For example, is "below 200°C" = "200 below"?

Answer 1

"Below 200°C" is not the same thing as "200 below".

• "200 below" means "-200°C". It refers to the specific temperature that is 200 degrees below zero degrees Celsius.

• "Below 200°C" refers to any temperature less than 200°C; it would include e.g. 150°C, 100°C, 0°C and -100°C.

"–200°C" and "200 °C" are simply two different temperatures, so "below –200°C" and "below 200°C" mean completely different things.

• "below –200°C" means (any temperature) "below 73 Kelvin" or "below -328°F".

• "below 200°C" means (any temperature) "below 473 Kelvin" or "below 392°F".

"below –200°C/–392°F" doesn't make sense in any context, because these are two different temperatures. Are you sure the text didn't say ""below –200°C/-328°F"?

The Wikipedia sentence, from the "Production" section of the article "Fluorine", doesn't seem to be talking about liquid fluorine. As far as I can tell, what it is saying is that steel is an adequate material for storing fluorine gas at temperatures below 200 °C (392 °F).

Industrial

Moissan's method is used to produce industrial quantities of fluorine, via the electrolysis of a potassium fluoride/hydrogen fluoride mixture: hydrogen and fluoride ions are reduced and oxidized at a steel container cathode and a carbon block anode, under 8–12 volts, to generate hydrogen and fluorine gas respectively. Temperatures are elevated, KF•2HF melting at 70 °C (158 °F) and being electrolyzed at 70–130 °C (158–266 °F). KF, which acts as catalyst, is essential since pure HF cannot be electrolyzed. Fluorine can be stored in steel cylinders that have passivated interiors, at temperatures below 200 °C (392 °F); otherwise nickel can be used. Regulator valves and pipework are made of nickel, the latter possibly using Monel instead. Frequent passivation, along with the strict exclusion of water and greases, must be undertaken. In the laboratory, glassware may carry fluorine gas under low pressure and anhydrous conditions; some sources instead recommend nickel-Monel-PTFE systems.

Answer 2

You haven’t read the English Wikipedia fluorine article properly. This says:

Fluorine can be stored in steel cylinders that have passivated interiors, at temperatures below 200°C (392°F); otherwise nickel can be used.

Nothing about super-cooled liquids! This is high temperature storage — I don’t know where you got it from, but the supercooling is wrong, and we are talking about a temperature below 473K, not one below 73K (to make it perfectly clear — absolute zero (0K) is –273˚C).

And below simply means below — in this case, below 200°C means from 0K to 473K.

In common speech one sometimes says “twenty below”, meaning “twenty degrees below zero”, as in the example from Merriam-Webster, below:

(4b) below zero — the temperature was 20 below

But never scientifically.