Pickling with Sulphuric

[Another JohnSParticipant @anotherjohns]

Posted by Neil Wyatt on 19/08/2016 12:46:30:

Loads of organic acids that do the same job well enough I can't see why anyone would use sulphuric.

Agreed – for the last couple of decades I have used citric acid – purchased from those "wine making" shops. Cheap and easy.

John.

[MuzzerParticipant @muzzer]

Posted by Roderick Jenkins on 19/08/2016 11:20:28:

Posted by Martin Kyte on 19/08/2016 10:39:55:

The idea of adding concentrated acid to water instead of the other way round is when you get a splash it's dilute acid and not concentrated.

Well partly that. The reaction between concentrated sulphuric acid and water is violently exothermic – that means it gives off heat. If you add a small amount of water to the acid the chemical reaction quickly heats up and boils the water. The rapid evolution of steam causes spitting and spluttering which will eject concentrated acid. Because there is an excess of concentrated acid the reaction will continue until all the water has reacted. Conversely, if you add the acid to water, the reaction is rapidly quenched by the excess water and the whole process is much more benign.

HTH

Rod

Edited By Roderick Jenkins on 19/08/2016 11:21:20

Rod is spot on.

The point with water into acid is that the more violent it is, the more quickly the water is further dispersed in the acid and the quicker the reaction then proceeds – a positive feedback mechanism. If there were a violent reaction with acid into water, it would only act to dilute the acid, slowing down the rate of reaction.

The overall release of energy may be the same but the nature of it is quite different.

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by Martin Kyte on 19/08/2016 12:16:28:

Not convinced Roderick. The heat comes from the hydration of H⁺ ions to form H₃O^{+ .} Not as one may suppose from the dis-association of the acid.

So the heat generated is only dependent on the quantity of the input reagents. It really does not matter if the reaction stops because it runs out of water or of acid. The heat produced is the same. It then becomes a calorimetry question as to temperature rise. As the water has a higher specific heat capacity than the acid the temperature will go up less when the bulk of the liquid is water as when adding acid to water. So the heat is produced by the chemistry which is the same in either case (ultimately you add the same quantities of acid and water together to get the desired concentration) but the temperature profile is down to the physics.

I think we are essentially saying the same thing which is add acid to water and the worst thing that can happen is a splash with dilute acid.

Personally I find the dry salts sold by many of the suppliers work perfectly well and saves all the bother of hard to obtain wet acid whilst avoiding the dilution issues.

best regards Martin

You might think that the rate of the reaction is an issue – but not, it seems: **LINK**

The great thing about any theory is that it needs to be validated by experiment. I'm now convinced that there is very little danger, despite what my chemistry teachers told me. I've still got half a winchester of conc. sulphuric and will continue to add it to water as required. When that runs out I'll move to something more friendly.

Cheers,

Rod

[Martin KyteParticipant @martinkyte99762]

As I said Rod chemically there is no difference. Physically there is although I agree that the danger is overplayed. I was commenting on the reasons not the results.

regards Martin.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 19/08/2016 12:46:30:

Loads of organic acids that do the same job well enough I can't see why anyone would use sulphuric.

The advantages of concentrated Sulphuric Acid compared with the alternatives are:

• Much cheaper in bulk
• Can be diluted to a wider range of strengths to suit particular needs
• Fast acting (particularly important in Industry)

The disadvantages for hobby use are:

• Ignorance likely to be severely punished
• Lots of 'wrong way round' advice on the web
• Reacts with many household and workshop items
• May be difficult to buy
• Safety issues in use and storage
• Acid proof apron, gloves and eye-protection unlikely to be available.
• May be too aggressive for comfort

I have concentrated acid available but rarely use it. I agree that most hobbyists would be wise to start with a milder alternative unless they know what they're doing and have a good reason for using the real thing.

Cheers,

Dave

[JasonBModerator @jasonb]

This one of his gets a bit more exciting watch from about 8.30

**LINK**

[Russell EberhardtParticipant @russelleberhardt48058]

Nice video Jason. It reminds me of cleaning stubborn glassware in the chemistry department at University using "popoff". It consisted of conc. nitric acid with a few mills of ethanol added (in a fume cupboard!)

Russell

[Brian HParticipant @brianh50089]

Posted by Martin Kyte on 19/08/2016 10:39:55:

The idea of adding concentrated acid to water instead of the other way round is when you get a splash it's dilute acid and not concentrated.

Martin

The real problem is that mixing the two generates heat and if you are adding acid to water the heat is enough to create bubbling and splashing which can be VERY painful.

[JAParticipant @ja]

The beauty of citric acid for pickling is that I do not want to mess around with strong inorganic acids. I got that out of my system at school and since then I would only do so if someone paid me.

There are much more interesting dangerous substances you could mess around with if you want to.

JA

 

Edited By JA on 19/08/2016 21:00:35

Edited By JA on 19/08/2016 21:01:19

[Gordon Brown 1Participant @gordonbrown1]

When I were a lad I worked for a gap year in a pharmaceutical research lab and one of the regular jobs was to clean sintered glass filters using chromic acid. I forget the exact recipe but the basics were a winchester of concentrated sulphuric acid, a couple of hundred grams of potassium dichromate and a small quantity of water. The acid was added gradually and very carefully to the water and dichromate mix but it became very hot indeed. The stuff was mixed in a very large beaker and kept in a fume cupboard. One day a colleague had mixed up the evil brew and picked up the beaker to move it to one side when the bottom promptly dropped out of it. A wave of acid shot across the fume cupboard and washed over the front lip, hitting my colleague about one inch south of his tackle. I was close to the sink at the time and was able to quickly turn on the tap that had a hose permenantly connected to it and wash him down. Despite this he suffered moderate burns to his legs and his trousers, socks and shoes disintegrated about him. All he was capable of muttering repeatedly was, "thank god I'm not two inches shorter….."

I've tried to avoid contact with acids ever since and still regard pickled onions with suspicion.

[mark smith 20Participant @marksmith20]

The nastiest stuff i`ve ever used was conc, hydrofluoric acid , you certainly don`t want to get any of that on you ,as its absorbed through the skin, and the burns are the least of your problems. And chemically its not considered a strong acid.

[AjohnwParticipant @ajohnw51620]

Rod is correct about sulphuric acid when water is added to it. It depends on the strength of the acid but the reaction of the water when it's added can be more like an explosion rather than some quaint chemical reaction that generates heat. If the acid is strong enough mixing just wont happen. The water can boil instantly.

It's pretty nasty stuff in a highly concentrated form and even when diluted due to the levels it will eventually settle to in normal ambient temperature ranges. That is dependent on the moisture in the air but it's why it can be spilt on clothes and appear to do nothing at all, for a while.

I don't know what the concentration of commercial acid is but I suspect it's higher than the one that battery manufactures tend to use for bulk storage and later dilution for actual use in batteries. From memory the specific gravity was up past 1.3. They don't care about weight just volume but do this because it far more stable and easier to handle than the highly concentrated forms. Even their level needs diluting the right way and don't forget to stir while adding acid to the water.

In a nutshell it's best to dilute the right way round what ever the strength is really.

I do have an indication of just how strong the commercial stuff is. I had used a pipette to measure some out and decided to suck water up to clean it out. Plastic pipette with just a film of acid left in it and it exploded shattering the end of the pipette. I don't do it that way any more.

John

–

Edited By Ajohnw on 20/08/2016 11:15:15

[Sam Longley 1Participant @samlongley1]

Concentrated sulphuric acid is called oleum ( cannot remember spelling) & has had chemical make up changed from h2 so4 to something like h3so4 ( suppose i should have googled it first it has been 60 years) & that is really dangerous stuff. At school only the teacher could handle it whilst we watched. He used to dilute it to make h2so4. Then we all got to do experiments with the stuff!!!

Can you imagine that being on the shelves in front of kids at school today

Edited By Sam Longley 1 on 20/08/2016 12:28:30

[Gordon Smith 1Participant @gordonsmith1]

Oleum is sulphuric acid with added sulphur trioxide.

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by mark smith 20 on 20/08/2016 00:10:18:

The nastiest stuff i`ve ever used was conc, hydrofluoric acid , you certainly don`t want to get any of that on you ,as its absorbed through the skin, and the burns are the least of your problems. And chemically its not considered a strong acid.

Horrid stuff. I developed a process for chemically polishing and then anodising tantalum crucibles using a cocktail of acids, mostly HF. Fume cupboards, shoulder length gloves, face shields – the lot. Anodised tantalum is lovely, the colour depends on the oxide thickness which, in turn, depends on the voltage applied. I liked a nice rich golden yellow which impressed the production guys.

Rod

[mark smith 20Participant @marksmith20]

I believe HF should be totally banned from use outside strict laboratory environments .

You can buy it freely on ebay at 40 % conc. which is very strong.

<LINK REMOVED>

If you look at the ad ,its says in Italian NATURA SALUTE BENESSERE which roughly translates as `natural health and wellbeing!!`

Absolutely ridiculous.

I used it at 70% conc. to seperate radioactive actinides like uranium, caesium.plutonium,etc… in a nuclear laboratory.

Edited By mark smith 20 on 20/08/2016 13:27:05

Edit by Admin: Link removed, I agree with Mark and I don't want to help any fool get hold of this stuff by keeping a link here!

Edited By Neil Wyatt on 04/11/2016 18:43:38

[JAParticipant @ja]

Posted by mark smith 20 on 20/08/2016 13:26:31:

I believe HF should be totally banned from use outside strict laboratory environments .

HF is a very important industrial reagent. Amongst other things it is used in the production of PTFE and as a flux for brazing high temperature alloys.

It was used at the zinc smelter at Avonmouth, Bristol, until its closure. Very occasionally hydrofluoric acid would escape into the atmosphere and etch the cars in local car parks including the smelter's. One local environmental group tried to start a campaign but, this was before the internet, could not find out very much about HF. The response of the local media was little better.

JA

[AjohnwParticipant @ajohnw51620]

I had a look around to see what it might be used for considering the other items on offer. No clues at all. He also offers phenol. I can imagine what that is used for.

Some uses are "interesting"

**LINK**

One thing I am pretty certain of this that various chemical substances have maximums that can be sent by post.

Their comments on what to do when damaged packaging arrives are worth a read.

John

–

 

Edited By Ajohnw on 20/08/2016 14:25:21

[Raymond AndersonParticipant @raymondanderson34407]

Just had a look at the site that Mark linked to, Something not right there !! had a quick look at some of the chemicals he is offering, and there is at least 3 that come under the "restricted " list, the aforementioned HF, Chloroform , and Phenol. He has 100 % feedback, so god knows how they manage to get that types of Chemicals delivered.

[Raymond AndersonParticipant @raymondanderson34407]

Looking further into the list there is 96 % H2So4 and 67% HNO3. A lot of the items appear to do with cosmetics !!! The HF [or any of the other acids mentioned ] will certainly have an effect on the complexion. It certainly wont improve , it, but it will change it

[Sam Longley 1Participant @samlongley1]

Years ago my father won a contract for the bata shoe factory in tilbury to renew the steel supporting the asbestos roof over their chromadising plant. The steel purlins had corroded due to acid fumes & had to be replaced so contract was to replace the steel. They thought he would also replace the roof but he saved money ( & made a tidy profit) by raising the roof & sliding the steel out bit by bit & replacing. Then lowering the roof onto the steel & re fixing the hook bolts.

All done by me and a gang over a holiday. So we worked over an asbestos roof over some 2ft deep tanks that had some 9mm ply sheets over them supported randomly by 3×2 timbers. We were 25 ft above on the asbestos a couple of hammers had dropped through & disappeared into the baths between the gaps in the unfixed plywood

After the job was done & the management were inspecting they started to have the covering removed. I asked what was in the tanks. "Oh they are the acid baths for dipping prior to chromadising"

So much for H & S 45 years ago

Edited By Sam Longley 1 on 20/08/2016 16:43:13

[MuzzerParticipant @muzzer]

IIRC, HF is used for frosting glass. Nowadays they often just use stick-on film, the name for which is "manifestation". You can only speculate how that name came about! God only knows?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Muzzer on 20/08/2016 17:18:31:

… the name for which is "manifestation". You can only speculate how that name came about! God only knows?

.

I thought at first that it was a spellchecker error; for that fine old Jewish firm of window-fitters <Manny Fenestration>, but no; it's the real deal, enshrined in legislation.

http://www.windowfilm.co.uk/graphics/manifestation-legislation

MichaelG.

[John LintornParticipant @johnlintorn87585]

Just to add my 10p. When doing my boiler I have found that kettle/dishwasher de scaler works well. It’s great if you have a mate who can supply you a source of acid but for the average Joe it’s not so easy. Whereas kettle design scaler is easily found in Tesco 😊

[pgk pgkParticipant @pgkpgk17461]

Acid is ridiculously easy to source… Brick acid (hydrochoric) from any builders merchant or sulphuric as drain unblocker (I bought mine from Wilco). Local hardware shop also has conc hydrochloric as their drain unblocker.

I'm following the book on my minnie build and went with sulphuric – it's quick but commonsense and taking care are important. Dropping a yellow hot lump of copper into a bucket of the stuff isn't the right time to have a panic attack or decide you need to take a deep breath or start fishing about in the bucket with bare hands. A second bucket of water is a good idea.

I've also handled nasty items in my time – a calm respectful approach with a contingency plan..

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