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Let's say I want to have the vapor pressure of mercury, as a function of temperature. I know that this information is available, for any specific temperature, from Wolfram Alpha, and I can also get the information in Mathematica by using natural language recognition, and typing something like "vapor pressure of mercury at 100C", say.

However, is there a Mathematica function I can use to, say, plot the vapor pressure as a function of temperature? If so, how would I be able to discover it? ElementData and ThermodynamicData do not seem to have that information.

I see that, if I type something like "height of Eiffel tower", it gets converted to something that has input form Entity["Building", "EiffelTower::5h9w8"][EntityProperty["Building", "Height"]], so in this example I can figure out what Mathematica function I could call to get the data I want.

However, if I ask for the above vapor pressure, all I get is a number with units. If I ask for just "vapor pressure of mercury", I do get Entity["Chemical", "Mercury"][EntityProperty["Chemical", "VaporPressure"]], and I found that I can ask for ChemicalData["Mercury", "VaporPressure"], but I'm not told under what conditions this vapor pressure holds (if I do ChemicalData["Mercury", "VaporPressure", "Conditions"] I get no information), and there seems to be no way to get the pressure for a specified temperature.

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    $\begingroup$ If push comes to shove, you can manually implement the equation detailed here. For serious work, I wouldn't use Alpha's values unless there was an explicit description of what formula (e.g. Antoine's) was being used, which it doesn't have. $\endgroup$ – J. M. will be back soon Oct 2 '16 at 7:06
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    $\begingroup$ WA uses many custom functions no present in the WL, and this is one of those cases, since "Mercury" is not an entity in ThermodynamicData. I believe the source in this case is here $\endgroup$ – Jason B. Oct 3 '16 at 14:20

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