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Can a *gas* be visible to the naked eye?

  1. Jan 28, 2008 #1
    I found this: https://www.physicsforums.com/showthread.php?t=105106

    But it the question was never really answered there. So I'd like to ask a *similar* question again.

    Are there any gases at STP, (without being "excited" or "liquefied"--see other topic, above) that are visible to the naked eye?

    My high school chemistry teacher told me that one of the defining properties of gases is that they are invisible, but I can't find any corroborating information. Google coughs up surprisingly little on this subject.

    Thank you.
  2. jcsd
  3. Jan 28, 2008 #2
    Chlorine and bromine are quite visible, although you don't really want to check. Likewise iodine and you just might find a picture of an old time vet sprinkling iodine crystals in a horse's hoof with the fumes just rolling out.
  4. Jan 28, 2008 #3


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    Look at the sky. It's blue. You're seeing gas. Were it invisible, the sky would be just as black during the day as during the night, and you'd be able to see stars.

    Your teacher is wrong, "invisibility" is by no means a defining characteristic of gases.

    - Warren
  5. Jan 28, 2008 #4
    Gas being a state, yes. Anything nearly can go to a gaseous state. Including water as steam, which is visible.

    Inert gases, which he may be referring to are a bit different. Some refer to them as the 'gases' because they resist other states and are quite rare. On the surface, anyways.

    Under most conditions, the inert gases are hard to detect. And are referred to as gaseous elements within the periodic chart. The do tend to be indiscernible when concentrated, unless reactions have caused them to link with other elements.
  6. Jan 28, 2008 #5


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    Steam is not visible.
    What are you talking about? You're misusing the word "inert." Perhaps you mean the noble gases which are indeed all invisible.
    There are many elements which are gases at STP and which are visible (most of the halogens, as has already been mentioned).

    - Warren
  7. Jan 29, 2008 #6
    Some gases have color such as halogens or NOx. You can see them in glass bottles or in types of fume, even leaking etc..
    Anyway, if you were in a medium of a colored gas, you could not see it.
  8. Jan 29, 2008 #7


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    It sounds to me as a very silly "defining property". What does it mean for something to be "visible" ? It means to be able to interact with light: absorp some of it, scatter some of it, or interact with it more coherently (refractive index).
    For instance, is glass "visible" ? Yes, mainly because of its refractive index. If the glass is of good quality, it doesn't scatter much light, nor does it absorb it.
    Well, gasses do have a non-trivial refractive index. It is the effect you see in summer when looking at a hot road, for instance. Now, their refractive indices, because of their low density, are small of course, much smaller than those of solids or liquids, but they are there nevertheless.
    You could just as well take as "defining property" of a gas that it doesn't have mass !

    Most definitely, gasses interact with light. Not as much as solids and liquids, but they do interact. BTW, if you take the ratio of the interaction with light of a gas with that of a liquid, and you take their ratios of their masses, then you find comparable numbers (order of magnitude). That means that saying that they are "invisible" (do not interact with light) is an error of the same magnitude as saying that they are "massless".
  9. Jan 29, 2008 #8
    I see steam out of things like a boiling tea kettle, when it screams. Am I crazy?
  10. Jan 29, 2008 #9


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  11. Jan 29, 2008 #10
    Note to other posters:

    There seems to be a trend in ~! of the Boolean order of a tautology.

    Please refrain in this...
  12. Jan 29, 2008 #11


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    What you can see is condensing liquid water vapour droplets (basically cloud), if you look just above the spout you will see a transparent gap where the water is still steam. Don't get too close -it's hot!
  13. Jan 29, 2008 #12
    So you have redefine what steam is. If steam is water in the gas state or vapour, then it is invisible. The 'steam' coming from a boiling kettle is water vapour plus very fine water droplets which you can see.
    You have a bucket of liquid nitrogen, and it also makes clouds which are merely fine droplets of water.
  14. Jan 29, 2008 #13
    Back to the point that seems most defied.


    as you can see in this readily applicable phenomenon, even metals may attain gaseous form, and do so easily. You see them line the street.

    Perhaps, rather than oblique yourselves, maintain an approach discipline.

    As, anyone that wishes may steam up there bathroom, and I assure you it's more of a gas than liquid. The two states are distinct. You;re convulsing with evaporation, and condensation.

    Being convolute as it where...
  15. Jan 29, 2008 #14
    Thank you.

    Thank you.

    This answer kills the idea of *all* gases being invisible, with a picture to confirm:
    TVP45: "Chlorine and bromine are quite visible, although you don't really want to check."

    And this answer may have been what my teacher meant, perhaps I misunderstood:
    chroot: "...Perhaps you mean the noble gases which are indeed all invisible."

    I'm 42, high school chemistry was a long time ago and it was the extent of my education in that area. I've held this incorrect idea about gases all this time. The subject came up for me when my son came home with a science project that involved states of matter.

    Thank you for helping clear this up (so to speak).
  16. Jan 29, 2008 #15
    No, you're thinking of water in the evaporative state: ie, humidity. Which typically invisible, unless it's dense enough to form clouds.

    Seeing through scope visioning as I can, you've tended the tendency. To blow everything up.

    When clouds are in a tempered environment. Guess What? The __gaseous__ state re-achieves the liquid state, and the more dense form falls to the Earth; yes! as rain.

    Now, if you can reasonably argue something massive as say a large cloud, that is definitely lighter than air when at an altitude, is nothing more than mystic water, then do it. I want to know you're logic, not contradiction.

    You're wanting to control the flow, of one state from another: Ice, Water, Water Vapor.
    Which, according to you, is something that can never be seen. In that line of logic, what state, may I ask, then is the cloud of which I spoke. It doesn't behave as a liquid, and there's a great deal of mass.
  17. Jan 29, 2008 #16
    Perhaps an objective lesson in the qualities of the 3 common states of matter:


    Where gaseous forms tend the general nature the 'dance' is around of:
    2)flows easily

    Whereas liquids don't tend to compress well.
    This is the 'key of' factor that is non-issued in this discussion.

    Many chose to assume it of themselves to go ahead an condense for everyone. But, I know for certain among many liquids the application of heat tends to create a less dense form at the surface, for most liquids.

    This causes, given conditions, an excited state where many molecules will escape surface tension. And, before diffusion sets in if allowed, be visible.

    Now, if one where creating 'pressure' of their own accord, then yes you could assume yourself the magna-Jason's Golden Fleece owner. And, things would behave in your depicted realities.

    But, as I now the process of distillation, this can't be. It relies to heavily on matter in the gaseous state. Which by the way can be substituted as vaporous. Since, there will always be interaction between molecules. And, they will attempt homeostasis.

    So many these days eat up time by assuming a critical process incorrectly to throw away 'Old Lines of Thinking'. But, an increase in heat will cause evaporation, and intense heat speeds it up. Until the escaping vapor becomes dense enough to be seen. But, as someone pointed out, only temporarily. A visible sign of diffusion, of which most gases readily behave.
  18. Jan 29, 2008 #17


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    pixel01 is correct, and you are not. Steam is, at atmospheric pressure, in excess of 100 degrees C. It is invisible. It will cause severe burns, instantly, upon any exposure.

    When someone says they've "steamed up the bathroom," there's no actual steam involved. They've really filled the bathroom with a fine mist of tiny suspended water droplets. The hot water from the shower evaporates readily, increasing the humidity in the bathroom until water begins to condense out into tiny water droplets -- a cloud.

    pixel01 described the process perfectly. You need to stop arguing about things you do not understand, as we do not take the spreading of misinformation lightly here.

    - Warren
  19. Jan 29, 2008 #18


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    Not sure what the point of all this rambling is, but it is incoherent.

    Here some information on steam...


  20. Jan 29, 2008 #19


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    Not to mention that it does not address the OP in the slightest. Steam is not a gas - it is the vapor phase of a compound. And yes, after years as a process chemist in a pulp mill, I can vouch for the fact that some gases are quite visible. We used a Rapson Generator to produce chlorine dioxide for pulp bleaching, and if the operator of that generator got a little impatient and added catalyst to the mix while you were sampling the product and trying to resolve the imbalance, you would be chased down the stairs by a colorful yellow-green cloud. Those wimpy little escape respirators were good for one breath, at the most, so you'd better be in shape. Of course, your underwear could be colorful, too. The sound of that huge steel pressure-relief lid slamming back into place was like a bomb going off.
  21. Jan 29, 2008 #20


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    I realize you're taking a beating here, but I'd also caution against using this as an example too. Though the OP just said "invisible", the implication was that s/he thought gases should be transparent. Since discharge and black-body radiation are completely different from the typical optical properties of transparency, I'd avoid this for clarity if nothing else.

    Of course, to be even more pedantic, we could even say that these lamps (and the sun) aren't filled with gases, but plasmas.
  22. Jan 29, 2008 #21

    is among the info on steam.

    in it...
    "...to transform a given quantity of a substance into a gas..."

    Everything I know of steam dictates it's a gas. Not what the temperature is, although that does indicate you shouldn't handle it.

    I realize, there again, the whole of the place doesn't turn to a sauna, where it is in a more contained dense area. And, that although in that particular incidence, there is condensation, your missing the point entirely.

    Of the original post, which was no gas is visible, you jumped. And, accelerated through "diffusive" tactics.

    If steam were just tiny droplets of water, I don't know, pressured past the normal state; then I think the term is mist. Not a gas, no. But steam contains more energy, and you simply have to see the difference amongst the water from which it came.

    I'll say this: Your of your opinion, I'm of mine. I'm unsubscribing this area for this post. The run has become insignificant to me.
  23. Jan 29, 2008 #22
    I know that the OP has already been answered but subsequent posts have produced confusing conclusions so I thought that I would add a few tidying details to clean things up a bit.

    As stated before, steam (in physical chemistry) is a gas and a completely invisible gas at that. There is a good amount of it in the air just as invisible as can be, all the time.

    As stated before, the visible component of the discharge of a teakettle so erroneously in our youth referred to a steam is actually tiny water particles, which is of course visible to the naked eye.

    In common speech as before alluded to, steam refers to the mist that accurse over boiling water. But in this context cannot at all be considered a gas.

    A cloud is made of water droplets, ice and gas. And although the water and ice is much more dense then the air around it, it stays aloft by the relatively warm air surrounding the partials making the overall density less then the air around it, there are other mechanisms as well. In short when you look at a cloud you are not seeing the water in its gaseous state but water droplets and ice.

    I hope that this post helps


    My references are both wikipedia articles as they are free and easy to reference. They can be found under "cloud" and "steam"
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