exchemist

Anyone who wears spectacles will know that you need a microfibre cloth to clean the lenses properly so that you don't get reflections, glare in sunlight etc. I don't know what an Apple cloth is but I suspect what you need is a cloth for cleaning lenses, not just any old piece of fabric. At any rate, that is what I use to clean the screen on my laptop.

Im not an expert on this but I wonder if the valves may not work so well with a compressible medium as they do with an incompressible one. If the %volume change of the pump chamber over its operating cycle is not that great, the pressure differences it creates may be too small to actuate the valves properly. This could explain why, when the pump is wet, you get better pumping, due to the moisture helping to seal round the edges of the valves, or else that it lubricates them so they function more smoothly. Whereas, when the pump is operating with a liquid medium, the pressure from whatever actuates the diaphragm will be instantly transmitted in full to the valves, because the fluid is incompressible, making the valve action more positive. But this is only speculation on my part, based on dimly remembered experience of dismantling an SU electric fuel pump on a Morris Minor I owned in the mid 1970s, when I was a student.

What is the Mohs scale hardness of each of these? What is artaclase?

If one thinks of the most widespread mineral material used by early man for building and for early artifacts, the rest can be confirmed fairly easily, using Moh hardness as a check.

Well of course. That's what several of us have been saying: when gases accumulate in hollows or high points, they do so because they are not mixed, i.e. before they have a chance to diffuse away into the general body of the atmosphere. The point we are taking issue with is your apparent contention, earlier in this thread, that mixtures of gases can spontaneously separate, or stratify, at least partially, under the influence of gravity. It is this that I am saying is not supported by your references.

Thanks. I've had a look at these but none of them seem to me to assert anything about gases concentrating themselves from a mixed state.

Well I am open to being corrected on the basis of solid evidence if you have any. If you have had to deal with methane accumulating in buildings you should find it easy to point to a standard, building regulation or paper that says methane or hydrogen will become more concentrated, i.e. with molecules moving against the concentration gradient due to difference in molecular weight. On the face of it, though, this seems ridiculous to me, though I do acknowledge that at very high artificial g forces, in a gas centrifuge, you can see a bit of partial separation due to this. This scenario will be where @sethoflagos's thermodynamic analysis has a practical application.

I've already answered this. If the gas is released as a stream (i.e. unmixed with air), it will do what you say until it diffuses into the surrounding air. Once it has done that it will not do what you say. This was also true of poison gas in WW1. After a while it dissipates. But this will be relatively slow for gases with high molecular weight, due to lower molecular velocity. There is no way that mixed gases will separate appreciably under the influence of gravity. You can do that sort of thing - very partially - in a gas centrifuge, but that involves very high multiples of g. You have yet to offer any reference supporting your contention that heavy and light components in the atmosphere will spontaneously separate , at least partially, under the influence of gravity.

Now it is you that is avoiding my question. What reference can you point to that says the atmosphere stratifies by gravitational separation of its constituent gases.

The lighter gases will diffuse downward. I do not believe they will spontaneously separate at high points, as you suggest. However if a stream of a light gas is introduced, that may rise initially, until diffusion or other processes dissipate it into the general body of air. This will be quite rapid, especially with hydrogen, due to the low molecular weight and consequent high average speed of the molecules. Have you a source for this idea that atmospheric composition changes with altitude, because of density differences between its component gases? I have not come across this. The compositional variations I am familiar with are due to chemical processes, e.g. ozone formation. If this indeed does occur, it must be a very small effect, detectable only over altitude differences of many km. Not something you would ever see in a building.

What intrigues me is how the risk of the microwave beam going off-target is managed. I see the beam is said to be too diffuse to harm living organisms. But I wonder about that, if the power being beamed is several GW in intensity. I can see they should be able to avoid the most obviously dangerous parts of the microwave spectrum, e.g. water absorption region, but it still seems a bit glib to me.

But again this is not spontaneous separation by density. Diffusion alone will mix gases of different density eventually. This should be obvious if you think what happens to a dense gas released into a vacuum chamber. It does not all collect at the bottom. That shows that molecular speeds are sufficient to far outweigh the effect of gravity on individual molecules. What may cause confusion is that the mean speed of molecules with greater mass is lower, at a given temperature. So their rate of dissipation by diffusion will be lower.

OK, give it a try then and let us know how it goes.

I don't think CaCl2 is too bad a health hazard, compared to alternatives. I can't help you with particle size of the CaCl2 as this will depend on where you get it from. As soon as it starts to absorb water from the air I think the particles will clump, suppressing any dust. But I wonder how effective your dehumidifier will be. The moisture of saturated air at 20C is 17g/m³, so in a room that is, say, a 3m cube you have about 450g (1 lb) water present. if the relative humidity is 100%. That will need quite a lot of CaCl2 to remove. You won't be able to collect any water, as what it does is absorb the water. As it is deliquescent, you will eventually have a concentrated liquid solution of CaCl2.

Yes I ignored that detail. (I too have done those courses, at my time on the refinery......)

A few things seem not to stack up here:- - If absorption were to increase "by logarithmic reciprocal", the absorption would get less with increasing concentration (partial pressure). That does not make sense. Can you post the formula you are referring to and provide a source for it? - According to my admittedly limited understanding of this subject, the CO2 slows down the rate of IR radiation loss to space by absorbing and re-emitting IR radiation as it ascends from the surface of the earth. If you double the partial pressure of CO2 I would think you would double the average number of absorption and re-emission events an IR photon encounters on its path to space. So the CO2 would trap double the amount of radiation. - The statement that CO2 will be a poison before it becomes a serious threat due to heat seems to fly in the face of everything that modern climate science is telling us. If you are asserting everybody is wrong and you are right about this, you have an uphill struggle on your hands to convince people. You will need to provide a very sound rationale. - While there are many gases in the atmosphere, we do know its composition pretty accurately and we know the IR absorption characteristics of all the components present. The challenge is in the complexity of the meteorological processes, e.g. interactions between atmosphere and oceans, clouds formation, icecaps etc, not the composition of the atmosphere. Nobody has ever pretended any of the models is "definitive" but they do all show the same basic trend - and we are seeing the predictions coming true. This is not about anyone "selling" anything. It is science.

What point are you making here?

I must say I see little value in this. By the way Quetta is a city in Pakistan.

No idea. Why don't you check it for corrosion?

They are the same, because rotation around a single bond is possible - unless there are specific steric hindrances from very large substituents, which a methyl group is not. Don't forget that the bonds in an sp3 hybridised C atom project in 3D, towards the corners of a tetrahedron. They don't stick out at 90 degrees in a plane, as shown in typical 2D representations like those in your example. If there were a double bond between C2 and C3 then rotation would not be possible and you could then speak of cis and trans isomers, depending on whether the substituents were on the same side or on opposite sides. In an sp2 hybridised C. atom, there are 3 bonds at 120degrees to each other in a plane, one or more of the bonds having some double bond character.

Petroleum jelly is the classic way, I believe.

Thanks for the explanation. I have to confess I have not used this stuff for about 40 years so I'm very rusty on the maths of it all, now, but the concepts intrigue me still. But I see @joigustakes issue with what you have said, so I'll sit back now and watch the debate. I don't know about editing equations on the forum. On the rare occasions I post one, I just do the best I can with regular text and the symbols library on my laptop.

So according to your link, CIA reports now take the form of handwritten bullet points that have no explanation and make no sense. For some reason the image of a hovercraft full of eels comes to mind...........

Hmm. I had understood it is the time-independent version that is an eigenvalue equation, which corresponds to a wave equation for standing waves, so it is not surprising that its eigenstates are purely oscillatory. Whereas it is the more general, time-dependent version that has the attributes of a diffusion equation. Well, not quite just electrons in atoms and molecules, but also molecules in vibration or rotation - and not forgetting the angular momentum of atomic nuclei, too. But mostly stationary states, it is true, though we do concern ourselves with the perturbation of the these states by EM fields and radiation, as in spectroscopic transitions and phenomena such as refractive index and magnetic properties of substances.

This is interesting. As mere chemists, at university we never delved into the significance of it being a diffusion equation. In most chemically relevant applications the time-independent version suffices, so there was perhaps little reason to do so.