Would any chemical other than water vapor make the air feel humid?
Not likely. Humid air feels humid because it inhibits evaporation of sweat from your skin, resulting in an accumulation of sweat (and heat) on your skin. The presence of other vapors in ambient air shouldn’t interfere with the liquid/vapor equilibrium of water, and so sweat should evaporate the same whether or not there’s a large concentration of chemical X in the air.
This doesn’t seem right to me. If the condensed state of a second vapor is well miscible with liquid water, quantitative properties for evaporation rate etc. are approximated by an ideal mixture, see here:
If a second vapor is immiscible with water I’m not sure how to think about it quantitatively, but if the properties of the compound and the amount of vapor present are such that it can condense onto your skin in any significant quantity, then it can surely also affect liquid water evaporation.
In practice I think that rather a lot of vapor would need to be present. You could certainly increase perceived humidity with other compounds, but is there any sufficiently benign compound that the primary noticeable effect might be that “it feels humid in here”?
We see clouds of chemicals which are not water on other planets, so if you could withstand the temperatures, the local atmosphere could indeed feel local version of humid.
I had the near misfortune of sticking my hand of heated vaporized ether…just before it ignighted:eek:
It did indeed feel like super humid steamy air. It was very warm so the temperature probably played a part in the hot humid feel
Not unlike leidenfrosting molten metal.
Former chemistry teacher nitpick:
The humidity in the air doesn’t actually inhibit the rate of evaporation of your sweat. Per unit of surface area, the rate of evaporation of a given liquid is dependent only on the temperature of the liquid. What is happening is that in a humid environment, the water in the air is simultaneously condensing on your skin. In a humid enough environment (100% relative humidity), you would have an equilibrium situation in which these two rates are equal, meaning that the net rate of evaporation is zero, and there is no net evaporative cooling effect (which is why humid environments feel so uncomfortable).
Yes, I am distinguishing between the rate of evaporation vs. the net rate of evaporation – I did say it was a nitpick. 
Which means that in an environment of non-water-humidity, the liquid on the surface of your skin might start out as mostly water, but it would end up as some mix of water and the other fluid.
That’s an unsound nitpick, in my opinion. You are conflating different levels of description, claiming that the molecular-level account of the process invalidates a perfectly good macroscopic description.
At a macroscopic level, the observation is that in high humidity your sweat evaporates more slowly. To say that high humidity “inhibits” the evaporation of sweat accurately describes the macroscopic phenomenon.
Your nitpick is that in the molecular-level account of the process, individual water molecules are not “inhibited” in their paths, rather it’s a dynamic two-way process. That’s correct, of course, but I don’t think it invalidates the macroscopic description. It’s a different level of description.
I disagree. In my nitpick, I’m describing what is actually happening (albeit at the molecular level), as opposed to what we think is happening, and by understanding what is actually happening, a greater and deeper understanding of the world around us is the result.
Again, I’m a former chemistry teacher. It’s quite useful to focus on the molecular-level description of evaporation, starting with rate of evaporation for a liquid in an open container, then moving on a discussion of evaporation in a closed container, and to then compare rate of evaporation to rate of condensation over time in that closed container. (The rate of evaporation remains constant, while the rate of condensation increases until equilibrium is reached). This not only leads into the first discussion of equilibrium in a typical chemistry class, but also covers the concept of vapor pressure in a closed container.
The upshot is that a lot of learning comes out of my nitpick, at least in an introductory chemistry course. YMMV.
I’m not disputing that the molecular account adds insight. I’m saying that there is no unique answer to what is actually happening, there are levels of description that can happily coexist for different purposes.
To take another example: the sun rises each morning in the east. An astronomical account of this would show that this is actually due to the rotation of the earth about its axis, not the movement of the sun. But it would be silly to conclude from this that the sun does not rise. They are different levels of description that can happily coexist for different purposes.
Again, I respectfully disagree. Of the two hypotheses that have been discussed in this thread, I believe there is one unique explanation here as to what is actually happening (though I admit that this statement is from the point of view of a former chemistry teacher, which is why I referred to it as a nitpick in the first place).
It would not be at all silly for someone who comes into the discussion and states at the outset that from an astronomical point of view, what is actually happening is that the apparent rise of the sun is due to the rotation of the earth about its axis.
There is a macroscopic observation that high humidity inhibits the evaporation of sweat, which is an accurate plain English description of what happens: your skin remains clammy and does not dry out. And there is a complementary molecular description that accounts for the macroscopic observation. These are not conflicting hypotheses, they are different levels of description, mutually consistent and both are correct.
Points of view is the entire issue. From the point of view of a couple taking a romantic morning stroll on the beach, the sun rises. From the point of view of the astronomer, the earth rotates around a stationary sun. These are not conflicting hypothesis, and one does not contradict the other, it explains it. The descriptions are consistent, both correct and appropriate in different contexts.
My counter-nitpick with you is with your insistence that the molecular level of description is the only valid one. It’s like saying: your feet are not really touching the floor, because electrostatic repulsion is stopping them.
And that’s what “touching the floor” actually means.
But I think that, especially in this context, the distinction between the two descriptions of the process is meaningful. If you have liquid water on your skin and walk into a highly-water-humid room, you’ll keep water on your skin: This much is explained by either description. But what if you instead walk into a room with high non-water humidity? In this case, saying that humidity blocks evaporation would lead to an expectation of dry skin, but the equilibrium description would imply that the skin would still remain wet, just wet with a mixture of both substances.
We seem to have settled into a discussion of semantics as to what is “right” vs. “wrong.”
This reminds me of the 1986 Isaac Asimov essay, The Relativity of Wrong, which can be read here in its entirety, or in an excerpt here. It’s worth a read.
Here’s an analogy you might find amusing. Think of molecules as hobos and heat as police enforcing anti-vagrancy laws. With lots of heat you only have individual hobos moving around. With less heat the hobos congregate (with individual hobos leaving and joining the group), and with very little heat they form a hobo camp.
Tricky. What you’re looking for is some nonideality in the mixture of gases in contact with your skin, which changes the equilibrium partial pressure of water. Since the interactions between the gas particles is already dominated by repulsions, by definition (since they’re in the gas phase), it’s hard to think of a way for an adulterant to lower the equilibrium pressure of water and make the air feel more humid. But perhaps a substance with a strong attraction to water, or which reacted readily with it in the gas phase, would raise the equilibrium pressure of water and make the air feel less humid.
Of course, given the general moistness of the body’s eyes, mucus membranes, lung tissue etc., being in contact with a vapor that has a strong chemical reaction with water sounds like a really bad idea, and the sensations produced by that reaction could be expected to overwhelm any perception of lightened humidity.
I think you are mistaken. Consider the case of a hypothetical compound X with virtually identical properties to water, fully miscible with water, closely approximating an ideal mixture. Adding the vapor of that compound will clearly have almost exactly the same effect as increasing the vapor pressure of water, and it will feel more humid.
As has been disussed, vapor X will begin to participate in the two-way process of evaporation/condensation at the liquid surface, leading eventually to a mixture of the two liquids on your skin.
What will happen in non-ideal cases where the two liquids are partially miscible or immiscible is more difficult to analyze quantitatively, but I think adding the vapor of any compound that has physical properties such that it will tend to condense on your skin will influence the evaporation of sweat to some degree.
Nitpick of a nitpick. The quoted statement is true only as a special case when the skin temperature is same as the environment’s temperature.