Acids

Still tidying up and sorting things out I went into my acids cupboard. Model engineers and pickling metals used to be pretty common. Dealing with them one at a time

I noticed some time ago that sulphuric seemed to be slowly eating into the plastic container that it was supplied in. I transferred it to a wine makers style demijohn and fitted a lab type rubber stopper some time ago. All ok.

When I did that the nitric was ok. Now it looks like something is happening to the plastic containers again. It has taken a long time, years.I think it's time to transfer that to a demijohn.

Hydrochloric which wont be concentrated but will be high strength no problem at all. Probably 80%. For what I need that for cement cleaner would probably do really.

I noticed an odd smell around the cupboard last week hence looking further. There were some metal parts in the same cupboard, all corroded suggesting fumes do escape even from screwed tight plastic containers.

My main reason for having these substances is diatoms and microscopes and I have received extensive training in the past about using them. Processing diatoms also involves mixing highly oxidising chemicals as well which really does need some care so please don't be concerned.

I am rather surprised about what has happened to the plastic though and some model engineers probably do still use strong acids and are also probably fully aware of what to do and not do with them. Odd thing is that some lab reagent bottles are plastic lined - I now wonder what happens to them. The one I have with sulphuric in it still seem ok. Why not make the containers from the same material. Cost I suppose plus most people who buy it probably use it quickly and or pour it into a vat of some sort.

John

-

John, when I worked with the acids you describe, they came in glass bottles with plastic caps/stopper. Hydrochloric and Nitric acids will give off fumes so the acids were stored in a ventilated cupboard, even then steel objects in the vicinity tended to turn brown. So yes, my experience is that strong acids may "penetrate" the stopper.
For pickling the few objects I braze I use citric acid, I don't any longer have a good place to store strong acids and citric acid works well enough for me.

Thor

Nitric and Sulphiric, isn't that Aqua Regia? Possibly vapours from both combining? Just a thought as I used Aqua regia to etch some very hard steel and the result was a total rusting of everything in the area! Even though ventilated.

Sulphuric acid doesn't fume, its vapour pressure at 25 degrees is barely measurable. HCl is the worst as it is a gas at room temperature.

Nitric acid boils at 83 degrees concentrated solutions will 'fume' unpleasantly and even less concentrated solutions can cause problems.

Neil

No. I think aqua regia is nitric and hydrochloric. I have noticed while using it that hydrochloric acid fumes and steel aren't a good mix.

It's pretty clear to me that the acid themselves are attacking the plastic without any help from the others. Sulphuric much quicker than nitric.

I'm currently waiting for another demijohn to dry for the nitric acid as tipping any concentrated acid into it wet wouldn't be a good idea at all.

John

-

I thought so and checked. Water in nitric acid raises the boiling point. I also think but haven't checked that both it and sulphuric acid are hygroscopic in concentrated form so absorb water from the air so 100% is nearly impossible to obtain. I vaguely remember seeing mention that 100% sulphuric is actually oily so concentrated doesn't usually mean what it suggests. Some nut cases process diatoms by boiling them in both to get round that. It wasn't a too bad a practice when people had coal fires as the fumes went up the chimney. Not sure what happens now.

John

-

Sulphuric acid is very non volatile and fumes will not escape from a plastic or glass bottle. Nitric and hydrochloric acids are volatile and the will escape through plastic but not glass bottles. If the plastic bottles are normal clear/translucent polyethylene bottle then at room temperature they should be unattacked by the acids. However, sometimes they are supplied in white polyethylene containers and these tend to be slowly attacked by acids. Chalk is often used as a pigment in white bottles and as the acid fumes diffuse into the plastic they react with the chalk liberating carbon dioxide and this causes the bottle to become covered with small blisters. This will happen fastest with concentrated hydrochloric acid and much more slowly with sulphuric acid solutions.

Mike

Mixture of concentrated Sulphuric and Nitric Acid is far nastier and more interesting, chemically, than Aqua Regia.

At school we used to dip pennies (old currency) into Aqua Regia and then Mercury. Then we would try to pass them off as half crowns. After two days in ones pocket the Mercury had disappeared and all you had was a bright clean penny.

In the sixth form we did use Sulphuric and Nitric Acid, as part of the classwork, to nitrate Benzene to make Aniline. I guess that this piece of chemistry is no longer part of the experimental classwork.

JA

The bottles were all translucent Michael. The first to look odd was the sulphuric. The nitric is now pretty opaque. Hydrochloric (80% ??) is still as it was but that probably came from a chemical supplier initially as it was to order. The others from an industrial supplier out of a tank.

There is also a small quantity of saturated oxalic acid solution in there but I don't think it would cause any of these problems at all. That's in a lab bottle anyway. That particular one will attack stainless to a certain extent. Also remove rust.

If I noticed that mercury had disappeared while in my pocket I would probably be a worried man. It's nasty stuff.

My father did the explode on touch stuff from iodine at school. I spent hours once trying to do that at home in early school days but did manage to make some nice fireworks, flour and coal dust explode but gunpowder just wouldn't work. Certain fertalizers too that didn't work. I'd guess no one does any of this sort of thing these days either.

John

-

> I'd guess no one does any of this sort of thing these days either.

Indeed, I feel like my daughter is missing out a whole chunk of a good education

Neil

JA In my days as a photographer I used to dip pennies into the exhausted fixer for a few minutes they came out silver plated, we also had to mix the used fixer with sawdust and send it off to reclaim the silver.re"> Neville.

These days people drink a lot of coke - that makes an excellent job of cleaning pennies. Probably useful after brazing copper too. Why not use coke instead and drink it afterwards. No point in wasting citric acid.

John

-

Might be better than missing a few fingers or other parts.

I don't think I would recommend drinking the coke after using it as a pickle. What would it have in it? Maybe copper phosphate? Is that poisonous? Copper compounds tend to be not good for you.
Mind you I wouldn't drink the coke before using it for a pickle either.

John

Copper compounds are toxic, so I wouldn't drink the coke afterwards either. And using coke would be more expensive than citric acid.

Thor

You took that seriously ?

As to the rest we are all victims of what is called the precautionary principle these days. The problem is that people apply it themselves and that in some areas it's applied by people that can't look at it logically and just think about what might go wrong and ignore any positives. In the extreme it might result in some people preferring not to even go out of the house or take extensive precautions if they do. There has even been signs of it on here - angle grinders. They can cause harm. They don't if used sensibly - that's the catch with many things. Lathes and milling machines are disappearing from schools because they have exposed rotating parts. Rather curious guards are fitted at times but the machines still go and get replaced by totally enclosed cnc machines. This happens because some one is worrying about what happens if some one stupidly grabs hold of a rotating part or runs the machine so fast that red hot swarf is flying off the machine so safety glasses are no longer adequate. And so it goes on and on.

There is a related side issue as well. One famous example is people at work being sent on a training course to teach them how to use a step ladder. Why - because a company may have to demonstrate that they have done everything they can to prevent people from falling off them. The lack of common sense by users isn't considered at all.

John

-

Edited By John W1 on 02/09/2015 09:59:18