I was discussing temperatures with someone a few days ago, and since they were American they wanted to change the numbers into Fahrenheit. Naturally I pointed out it was a silly old fashioned scale to use, but I couldn’t remember much about it’s origins. So onto the internet:

According to wikipedia:
According to an article Fahrenheit wrote in 1724, he based his scale on three reference points of temperature.[7] In his initial scale (which is not the final Fahrenheit scale), the zero point is determined by placing the thermometer in brine: he used a mixture of ice, water, and ammonium chloride, a salt, at a 1:1:1 ratio. This is a frigorific mixture which stabilizes its temperature automatically: that stable temperature was defined as 0 °F (−17.78 °C). The second point, at 32 degrees, was a mixture of ice and water without the ammonium chloride at a 1:1 ratio. The third point, 96 degrees, was approximately the human body temperature, then called “blood-heat”.[9]

Well first of all I realised that the Fahrenheit scale made much more sense than I had thought it did.
Then I noticed the use of ammonium chloride brine. NH3Cl was probably discovered in the middle east and spread by Islamic alchemists from the 8th century or so onwards. It can be used to clean metal or make various chlorides such as Mercuric Chloride and plays an extremely important role in European alchemy.

Therefore, amazingly enough, because of its use by alchemists, then chymists and finally chemists, it was readily available and someone had worked out that a brine solution of it had such an interesting property as reaching a regular, predictable stable temperature. Without the this inheritance of substances and how to manipulate them, Fahrenheit may not have been able to produce his scale in such a way.

The term ‘frigorific’ is explained a bit better here:
Seems to be an interesting blog on chemistry with a tag line at the top that I should steal – “Chemistry is not a world unto itself. It is woven firmly into the fabric of the rest of the world, and various fields, from literature to archaeology, thread their way through the chemist’s text.”

So, a new word and a nice connection through substances between modern chemistry and alchemy.