Pickle

You can also buy glacial acetic acid from auction sites and dilute to your choice. Take some commonsense care.

pgk

That's good advice Russell and I'd suggest taking even more precautions when handling strong Acetic Acid. Chaps seem all too happy to believe dilute Sulphuric Acid is hideously dangerous while Acetic Acid is completely safe: far from it!

No excuse these days for not looking chemicals up on the Internet. Read the Material Safety Data Sheet (MSDS) for the item concerned and take due precautions. Acetic Acid has a cuddly safe reputation because we're familiar with Vinegar. Yes you can eat Vinegar in small quantities, no you wouldn't want it in your eyes. Strong acetic acid is a lot nastier: it can burn skin, blind, and you don't want to breath the fumes.

Gloves, googles, careful pouring, good ventilation and other simple precautions are often sufficient to de-risk most operations. I suspect most Model Engineers are careful in practice, even those gung-ho about H&S on the forum. My other hobby (Amateur Radio) is a good deal more dangerous. Not due to electrocution as you might expect, more usually inexperienced chaps falling off something high whilst erecting antennae.

Dave

Edited By SillyOldDuffer on 22/07/2018 10:26:38

Noo! Not quite! Take all precautions to avoid spilling any concentrated sulphuric acid on oneself. There should be no chance of ‘splashing’ it directly onto skin. Even 5% acid splashed on the skin requires plenty of irrigation to avoid irritation - or worse.

Concentrated sulphuric acid simply removes water from wherever it might get it - even as water combined chemically in tissue, leaving behind carbon as solid, in many cases. So on skin, it removes water from it.

Try it on sawdust - you will be left with charcoal! Or perhaps best not to try it.

Concentrated nitric acid on sawdust will likely cause it to go up in flames.

One is a desiccant, the other an oxidising agent. We used conc sulphuric as a desiccant in chemistry-type desiccators when it was appropriate.

Concentrated hydrochloric acid is pungent but probably not as dangerous as the other two (as long as not affecting the eyes!). Dissolves most metals, especially if there is nitric acid, as an oxidising agent, in it (aqua regia) when it will even dissolve precious metals. As an aside, hydrochloric is usually used with chlorine (as an oxidising agent) for dissolving precious metals these days - recovery of the last traces of dissolved precious metals, from the bulk solutions used, is impossible while any oxidant is present. BTDT.

Agreed, so what are you objecting to? I have found from experience that 5% sulphuric acod splashed onto the skin is not problem if washed off within minutes however I always wear goggles and gloves when pickling copper. In school metalwork in about 1960 we were not even supplied with those, just tongs.

Russell

Russell,

Sorry, but you were not too ( no, ‘not absolutely&rsquo clear, referring to concentrated sulphuric acid and 5% in the same paragraph.

Someone reading that may not understand that there are differences between the former and latter. As I said - not quite!

Yes, I’ve washed my hands in dilute hydrochloric acid before now (rinsed off, afterwards), but some may have far more sensitive skin than I had back in those days. I also know that sulphuric acid is non-volatile and will concentrate somewhat from a dilute solution, as the water evaporates. So after rinsing in water any splashed clothes really need an alkaline rinse is required to avoid holes in those clothes, later.

Directions for use of chemicals needs to be clear and totally unambiguoius. Having dispensed hundreds of 50 litre carboys of acids and alkalis into reaction vessels, I know not to mix concentrated and dilute warnings in the same paragragh, as you did. I’ve seen the effects of chemical mishaps, and prevented a few, in my lifetime.

I hope that is clear.

.

What on earth are those pesky 'auto-smiley' things up to now ?

MichaelG.

Hi guys, I have been doing jewellery for many years, I am not sure what metals you require the pickle for, but for silver the safest by a country mile is aluminium sulfate. 90% of all jewellers use it nowadays.

It is sold as "Safe jewellers pickle" and because they fail to leave out the msds, they charge far more than it is worth, but it is nothing more than aluminium sulphate. I am sure it will work on copper/brass and bronzes to.

I hope this helps someone,

Pete

residents of Camelford might not agree with that.

Hi thanks, aluminium sulphate seems easy to get and safe but what concentration do you need. I notice the stuff on eBay says it's 17%.

A question for the chemists please;

I have about a 2 1/2 litre bottle of 95% sulphuric acid that is about 30 years old and I have noted the new laws to come into force in November.

I can very carefully dispose of the contents by heavy dilution etc but does anybody know how to safely dispose of the bottle that will now have traces of the acid inside. There are warnings about adding water to the acid if I was to rinse it out. Can any of the chemists out there explain how to do it please?

Phil H

I also have both part used and unused sulphuric about. Should I need to dispose of it then dilution and subsequent neutralisation is the way to go (as in add something like chalk). As for the bottle... lower it into a bucket of water with sensible care; mouth of jar away from you and decent washing up gloves/glasses.

pgk

The hazard of adding water to concentrated acid is if you get a splash it's an concentrated acid splash. This doesn't really apply if you are rinsing out a bottle where the acid is very much less than the water you are pouring in.

regards Martin

There is a danger with dilute sulphuric acid. if it is splashed on a surface the water tends to evaporated leaving concentrated acid. Watch how you hold lead acid batteries, I remember that if held against my overalls, the front of them got eaten away in a fairly short time. The supposedly "spill proof" batteries that we used in aircraft weren't.

Ian S C

OK, thanks guys I will do that and I also have some home brew citric. I might do a comparison test (sulphuric vs citric) with some dirty copper to see how it goes. I suppose the very least I could do is to make an acid bath (below 15% sulphuric) before disposing of the sulphuric bottle.

Phil H

No need to test it Phil, Sulphuric Acid out-performs (ie works faster) than Citric Acid, even hot Citric Acid.

The ideal pickle is cheap, reacts quickly with oxides, and doesn't produce toxic waste, or leave an insoluble mess on the item being cleaned. Dilute Sulphuric Acid, if you can get it, is good stuff. Industry use it in large quantities because Sulphuric Acid is fast, cheap, easy to clean off, and the waste is manageable. If you're lucky enough to own some sulphuric acid, why not buy some bigger plastic containers and dilute what you have down to pickling strength, store it somewhere safe, and use that?

Hydrochloric Acid isn't ideal as a pickle because it breaks the 'easy to clean off' rule. Unlike Sulphuric Acid which has an affinity for water and is straightforward to rinse, Hydrochloric leaves difficult to remove chloride ions inside the metal's pores creating corrosion sites. After a few years any surface protection is punctured from underneath allowing water and air to get in and finish the job.

I think I understand why Aluminium Sulphate would clean Silver, but not why it might be good for steel. Anyone tried it?

Dave

Thanks Dave, I am beginning to think that way. When I had a go at a boiler many years ago, I had an old, plastic paint type container safely under a very robust bench. It could take half a boiler length in one dip and lasted for ages. And you are right - I could store a large container down the side of the house 'SAFELy' of course - as long as my wife doesn't know about it.

Phil H

Sorry for hijacking the thread but if there are 2 litres of 95% acid and I mix them 10:1 with water (to be diluted to 30:1 when needed) that would give 2 off legal 10l storage bottles. Is that about right?

Phil H

If (big if) I got the sums right, that's OK

You can't legally own stronger than 35% by weight.

As 2 litres of fully concentrated acid weigh 3.7kg you need about 10 kg of water to dilute it to 37%. 10 litres of water weighs 10kg, and your acid is 95%, so job done.

Dave

When is this army of government inspectors going to search every hobby-shed?

Of course we live in a society of mind-numbing rules where every A&E dept has to have a green first aid kit.

pgk