Temperature Scales

In the column http://www.straightdope.com/classics/a4_188.html
Cecil gives the oft-quoted value of 98.6 for the temperature of humans. Are three significant digits really appropiate?

Any midwestern kid understands the sensibility and utility of the Fahrenheit scale: Any weather above 100 or below zero means that school is cancelled. What could be easier?

Yep, 98.6F is the same as 37C, which is only two significant figures, as it was when the study was done originally, as I understand it. Are you sure Cecil never commented about this? I thought that’s where I learned it. Drop him a line.

Of course, 98.6 has become iconic.

Well, hell, I just looked up another reference, and it says that average human body temperature is in the range 98.4F to 98.6F, so maybe three significant figures is justified.

The real reason the temperature scale is 32 and 212:
Farenheit was using the freezing and boiling points of salt water. Salt water freezes at 0 and boils at 180. I’m not sure why 180 was chosen for the freezing point bu it is one half of the number of degrees in a circle (a semi-circle if you will). The circle is a perfect geometric shape, so this might be the reason.

John T.


Alone we can move buckets; together we can drain rivers.–Mike Brady, from the Brady Bunch movie

Midwesterners close the schools if the temperature cranks up above 100? Hell, where I went to school we didnt even notice it was warm until it got up above 105. But then, if it got below 50 we all thought we would die of frostbite. :slight_smile:


the Artist Formerly Known as Kara

[Farenheit was using the freezing and boiling points of salt water. Salt water freezes at 0 and boils at 180. I’m ]
the freezing pt. of a mixture of salt and water will vary according to the quantities of each.
sea water will freeze at a temp closer to 32 then 0, I think it is 28, but not sure. I do know that a canal on the inside of a barier reef island that I used to live along would freeze when temps were above 0, usally in the teens, sometimes in the 20’s depending on factios as sun/wind/current. now admittaly the water was not exactly sea water since it is an estuary, but it is pretty close. Also I would thing that salt water would have a higher boiling point then fresh.

0 Fahrenheit was quasi-arbitrary. IIRC, he was looking for a temperature that could be created but lower than which ambient temperature was not likely to go. Obviously, in the winter it got below the freezing point of water; it might even get below the freezing point of seawater.

What he set 0 at was the freezing point of a specific-proportion brine mixture. Exact components escape me, but it was not seawater but a more concentrated brine, with some other “antifreeze” component included.

Regarding the remark on boiling a salt solution at 180 (dgrs F - I assume).

A saline solution boiling at 180 F?
Not true! A solute surpresses the boiling point, thus the boiling point of any solution is elevated above the normal boiling point of the pure solvent. (Normal boiling point refers to boiling at atmospheric pressure.)
Hence, a salt solution will boil above 212 F.

And, if curious, the steam coming off a
salt solution will be superheated steam because the temp of the water vapor is now raised above the normal boiling point.

The parallel drawn between 180 dgrs in a semi-circle is bogus.

…But, don’t get all steamed up over this!


I’d rather have a bottle in front of me than a frontal lobotomy - Hawkeye 4077th

Slight Correction to above:
I meant to say “surpresses boiling” thus raising the normal boiling point.

I hope you got the gist!


I’d rather have a bottle in front of me than a frontal lobotomy - Hawkeye 4077th

Not to nitpick, but you mean “boiling point elevation”. The freezing point is what is supressed by a solute.


“I had a feeling that in Hell there would be mushrooms.” -The Secret of Monkey Island

My thanks to Diceman on the subtle clarification.

Yes, freezing point is suppressed and the boiling point of a solution is elevated by a solute. However, {see my submitted correction}, it is also correct to say that the physical ACT of boiling a solution is suppressed by a solute.

In the field, it’s quickly spoken of as “boiling is suppressed” which implicitly includes the fact that the boiling point is elevated.

Hope this helps clarify!


I’d rather have a bottle in front of me than a frontal lobotomy - Hawkeye 4077th

Tangentially, how do you interpret “turn down the air conditioner”? :slight_smile:

I ask the person if they want it colder or warmer.

The inventors of penicillin, the polio vaccine, and DDT.

What in the world was that about, drewder?

Sounds like a Carnac question…

Somehow got posted to the wrong thread. Odd because I don’t think I have ever looked at this thread before.