Sciencemadness Discussion Board

External silvering of glass?

Toady - 18-11-2016 at 14:28

Here be a thought that just thunk itself.

Many times, although I don't as yet own one, I've seen various bits of silvered glass, usually condensers.

This is, is it not, in the internal surface of the outer jacket of the condenser?

Whilst I don't have the capability of course to open it and perform that operation on a jacketed column, is there any reason why it shouldn't be just as effective done externally as internally? or at least, if not equally efficient, then it should at least keep the temperature from rising somewhat.

Anybody know how well a pair of condensers of equal type, size and quality would perform side by side in identical conditions, the only variable being one silvered (with a single layer, on the inner layer of the coolant jacket) and one silvered on the external surface of the jacket?

Because I was thinking, why not buy a condenser, and use the Hg gilding process, evaporating the residual Hg within a chamber lined with gently sintered flowers of sulfur? just enough so it doesn't fall away as powder, but so Hg vapour can effectively enter it. Perhaps an initial solid coating of sulfur within a box, to allow adherence of the matrix-to-be, and then covering with a damp paste of calcium carbonate or bicarbonate and sulfur. Heating rapidly so as to briefly melt the sulfur, adhere it onto the layer bound to the chamber surface, and then dissolution of the carbonate/biicarbonate using dilute HCl (dilute so as not to evolve too much gas in too brief a time, thus leaving behind, after washing, a matrix of solid sulfur, although delicate, hopefully enough to allow for recovery of Hg, after gilding the surface of the glass with a silver mirror.

Thought being that it would be useful for thermal control in case of condensers, and flasks both, but in the case of a flask, if one were to fully gild the outside then it could be used as a flask dedicated for performing reactions with light-sensitive reagents or reaction precursors?

And a final thought that occurred to me right now, is creating a metal mirror of a more resistant metal, followed by covering in a suspension of calcium hydroxide, since its insoluble, with colloidal (insert precious metal of choice), for ambient and low-pressure catalytic reduction. Nickel even. Sort of like, after dissolution, and adherence of lightly sintered (since for a colloid it would take little energy to do so) the metal particles together, and adhere them onto the wall of the flask (internal surface) then dissolving away the support, or in the case of such a 'reduction flask' keep the particles of the colloid away from each other to a degree, prior to dissolving away the lime with acid?

Is this pointless, has it been done, or is it known to work.

Apologies for not UTFSE, but I am not at my own computer and must get off it literally, right this minute.

Thoughts on my ideas anybody?

Maroboduus - 18-11-2016 at 15:25

Brashear's process and the rochelle salt process would be much safer, and more likely to actually stay stuck on the glass.

I have never seen a silvered condenser other than the occasional Dewar condenser for dry ice/solvent uses.

Sometimes vacuum jacketed fractionating columns are silvered. You could save some money by silvering a vacuum jacket column yourself, but external silvering would be more vulnerable to mechanical wear and corrosion unless coated to protect it. Obviously the outside doesn't get very hot so even an epoxy would probably last in such an application.


You sentence structure is really screwed up. It hard to see what you're talking about at times.

Plating a catalyst on the inside of a flask: Why would you want to do that? Easier just to throw it in there. On a support if it needs it. A little charcoal has more surface area for catalyst support than a big flask does. And when the catalyst is spent, or needs regenerating scraping it off the inside of a flask would be a huge pain in the ass.


j_sum1 - 18-11-2016 at 15:29

First. Silvering using ammonia is so straightforward, I am not sure why you would go for an Hg process. https://youtu.be/ti_E2ZKZpC4?t=12m18s

Second. Silvering the inside of a container is pretty easy since you can just pour your solutions in and shake. I guess if you wanted to silver the outside you could immerse it in a large bucket and stir but that seems a more awkward process.

Third. One advantage of silvering the inside is that it is less prone to scratching. Sure you can protect it with an additional layer of something as you have suggested. I'd be looking up some methods that are tried and true for my specific purpose if I was to go in that direction. Why reinvent the wheel?

Fourth. Both forms of silvering that you have proposed are likely to have very similar reflective properties and so will be comparable.

Fifth. I am not really sure what your purpose is here. I know that silvering of reaction vessels is sometimes done and I think it was more common in bygone days -- you occasionally see antique glassware with silvering. But for a condensor, I am not at all sure what you are trying to achieve. A condenser works by conduction and forced convection of heat. Silvering limits radiation which in the context of a condenser will have a very small effect if any. I have really only seen silvering for light-sensitive reactions. But it does not seem like you have a clear purpose for what you are doing. We cannot possibly answer your question "Is it known to work?" unless we know what "working" actually means. And for that you need to have a defined objective.


[edit]
ninja'd by Maroboduus on every point. :)

[Edited on 18-11-2016 by j_sum1]

Maroboduus - 18-11-2016 at 15:50

Quote: Originally posted by j_sum1  
First. Silvering using ammonia is so straightforward, I am not sure why you would go for an Hg process. https://youtu.be/ti_E2ZKZpC4?t=12m18s



Second. Silvering the inside of a container is pretty easy since you can just pour your solutions in and shake.


[edit]
ninja'd by Maroboduus on every point. :)

[Edited on 18-11-2016 by j_sum1]


Not Quite. It never occurred to me that you could do the inside of something by just pouring the solution (or solutions) in there.
I was vaguely wondering how they do the inside of vacuum jackets as I wrote this, but didn't see the light.

Dr.Bob - 18-11-2016 at 16:34

All you need is silver nitrate and a reducing agent, aldehyde or sugar works. Silvering the inside of a vacuum flask protects the silver, as it dissolves in many acids and would tarnish quickly in most labs, so putting it inside the sealed vacuum part is the best way to keep it shiny. And catalysts need lots of surface area, so a smooth, shiny, plating would be terrible for creating surface area, so likely about as good a rock as a catalyst. That's why Suzuki's usually stop working if the Pd(0) plates out on the flask. And if you are trying to protect things from light Al, foil does well.

Toady - 20-11-2016 at 08:32

The catalyst-impregnated flask thing was pretty much an afterthought and that I hadn't much time (a minute or two) before someone needed the computer I was using.

Main thing I'd be wanting to do is reduce the heat loss from a dry ice condenser, to slow the loss of coolant when liquefying gases.