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Old 17th Aug 2022, 8:04 am   #1
mark_in_manc
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Default 'Spirits of Salts' as soft solder flux?

Hi folks - not sure where to put this, but I'll try here.

I have a vague memory of an old, now-late, friend telling me he used 'spirits of salts' as a soldering flux - in his case for soldering nipples onto the end of oily old cables for things like bicycle controls.

Having struggled with an OT soldering job lately, and failed with what I would view as 'normal' brown flux, I guessed that someone here would have experience with this, and some ideas to offer. Its suitability for electrical soldering, soldering to dirty chassis, tin-plate sheet work, as well as nipples on cables (perhaps an occasional UKVRRR need to do this) would all be of interest to me.

Thanks
Mark
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Old 17th Aug 2022, 8:10 am   #2
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Default Re: 'Spirits of Salts' as soft solder flux

Another good tinning agent is ammonium chloride. It is quite possible that brown flux does contain a trace of HCl, given the green residue which can occur when used for soldering copper pipe, if the joint is not cleaned after soldering. The key to any soldering job is to ensure that the items to be soldered are clean & bright to start with and if using additional chemical agents to help, ensuring that the job is wiped clean afterwards.
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Old 17th Aug 2022, 8:12 am   #3
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Default Re: 'Spirits of Salts' as soft solder flux

"Spirits of salts " is hydrochloric acid. But what are you calling "normal" flux? The flux suitable for electronics is rather mild. An acid soldering flux for mechanical soldering will be much the same in effect as HCl and is also very corrosive.

It makes the soldering easier but the cleaning up afterwards much harder!
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Old 17th Aug 2022, 8:19 am   #4
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Default Re: 'Spirits of Salts' as soft solder flux

Having learned my chemistry from obsolete textbooks originally owned by my grandfather, I recall that ‘spirits of salt’ is the old name for hydrochloric acid. ISTR it being the original flux used when I was taught soldering by my father with a big gas-ring-heated iron. Later, in my apprenticeship, it was used in sheet metal soldering. I’ve always found it very effective, but it does need washing off thoroughly!

I have seen bottles of descaling fluid labelled ‘spirits of salt’, but haven’t tried it as a flux.

Martin
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Old 17th Aug 2022, 8:53 am   #5
Denis G4DWC
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Default Re: 'Spirits of Salts' as soft solder flux?

The first time I came across this term was when an elderly friend, ex RAF, and now departed, explained to me how he made a radio whilst in a POW camp during WW2. Amazing how resourceful some of these guys were.

He assisted the Camp Dentist so was able to export!! a few items including some Hydrochloric Acid which he mixed with Vaseline, that came in the Red Cross parcels, to make a soldering flux.

Denis
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Old 17th Aug 2022, 8:54 am   #6
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Default Re: 'Spirits of Salts' as soft solder flux?

Rather than try to use plain hydrochloric acid as a flux, the best flux for soft soldering steel is "killed spirits" or zinc chloride. Commercially available as "Bakers fluid", it is easily made by dissolving small pieces of zinc in hydrochloric acid untill no more will disolve then straining the solution. It is still corrosive, so does need rinsing afterwards. I use it regularly for soldering nipples onto motorbike control cables. As with all soldering operations, the cleaner the parts, the easier it is to get a reliable bond.
Rod
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Old 17th Aug 2022, 9:03 am   #7
John M0GLN
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Default Re: 'Spirits of Salts' as soft solder flux?

A safer flux to use than 'Spirits of Salts' is 'Killed Spirits of Salts', it's made by adding Zinc to Hydrochloric Acid to get Zinc Chloride, Bakers Fluid and Fluxite I read contain Zinc Chloride.

John

Edit, I see I've come in second again.
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Old 17th Aug 2022, 10:25 am   #8
emeritus
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Default Re: 'Spirits of Salts' as soft solder flux?

On the workshop course Plessey sent me on at the local technical college, the flux used for soldering tinplate in the sheet metal module was killed spirits. I still have, and use, the tinplate oil jug and funnel I made there more than 50 years ago, so I guess I must have cleaned away the excess flux effectively!

A few years ago there was an item in an electronics magazine about a US firm that decided to experiment with environmentally-friendly replacements for some of the chemicals they were using. Apparently they found that lemon juice made an excellent flux for electronics circuit boards assembly, as long as the boards were washed after soldering, which they were anyway.

Last edited by emeritus; 17th Aug 2022 at 10:40 am. Reason: typos, lemon juice added
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Old 17th Aug 2022, 12:51 pm   #9
Roger Ramjet
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Default Re: 'Spirits of Salts' as soft solder flux?

Aah memories of soldering motorbike cables, especially when "Ape Hangers", became the fashion after the Easy Rider Film was released. I did several conversions & got along fine with normal plumbers brown flux although of course these were brand new cables that had not been oiled.

To get back on thread, what is wrong with today's multicore solder ? I can never seem to get a good joint which was neveer a problem in the 70's & 80"s. Rog
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Old 17th Aug 2022, 1:02 pm   #10
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Default Re: 'Spirits of Salts' as soft solder flux?

Quote:
Originally Posted by Roger Ramjet View Post

To get back on thread, what is wrong with today's multicore solder ? I can never seem to get a good joint which was never a problem in the 70's & 80"s. Rog
It might be the dreadful 'unleaded' stuff that's being sold now. You need to look for the good old 60/40 leaded solder that we've grown up with.....
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Old 17th Aug 2022, 2:47 pm   #11
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Default Re: 'Spirits of Salts' as soft solder flux?

Get yourself a tin of Telux plumbers flux like this one.

https://www.unitedindustrial.co.uk/i...html?vid=46805

I actually bought it to solder the last mm or two of the steel cables on my sons bike so I could easily dismantle it. I never liked the idea of those crimp on nipples.

It is a paste so is much easier and safer to use than having corrosive liquids running all over the place. You still have to wash off any remaining flux under the tap as it is still slightly corrosive.

Don't use your best soldering bits as it does erode the plating quite quickly. Ideally an iron like the old Henley solon with it's solid copper bit is the way to go.

Al
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Old 18th Aug 2022, 6:35 am   #12
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Default Re: 'Spirits of Salts' as soft solder flux?

If you do use any of the corrosive fluxes, especially "Spirt of Salts", Hydrochoric acid, be very careful not to breath the fumes.

Peter
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Old 18th Aug 2022, 7:24 am   #13
mark_in_manc
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Default Re: 'Spirits of Salts' as soft solder flux?

Thanks all. I obtained some SoS sold as drain cleaner and yes, it fumes like hell. It also came in the post, which surprised me as it is 25% HCl. So I'll have to try a little with some scrap wheel balance weights in (which when they are not steel, are now zinc thanks to control of lead regs) and compare the two.

I guess failing to neutralise the flux leads to corrosion - maybe a little alkali (I have some caustic soda) might be appropriate, though I can imagine an unstable feedback situation where my workpiece 'hunts' wildly around PH7 as I hit it with one after the other!
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Old 18th Aug 2022, 8:03 am   #14
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Default Re: 'Spirits of Salts' as soft solder flux?

Quote:
Originally Posted by mark_in_manc View Post

I guess failing to neutralise the flux leads to corrosion - maybe a little alkali (I have some caustic soda) might be appropriate, though I can imagine an unstable feedback situation where my workpiece 'hunts' wildly around PH7 as I hit it with one after the other!
Washing Soda which is Sodium Carbonate is much safer to use.

John
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Old 18th Aug 2022, 9:56 am   #15
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Default Re: 'Spirits of Salts' as soft solder flux?

And, Mark,
Don't forget to advertise the fact that you have used acid flux to solder.
It would just be nice to know that in a year ot two my precious amplifier, purchased in Manchester, with said transformer has dissolved into snot on the corner of the chassis.
OT I "figure " is output transformer??. Try a little 600 or 800 grit wet n dry paper. NO ??
try a fine small file. Abrasive file maybe.
WHAT sort of varnish was used in the original construction of the said OT ?.

With all my suggestions meant in best humour.

Joe
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Old 18th Aug 2022, 10:23 am   #16
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Default Re: 'Spirits of Salts' as soft solder flux?

If it's metal chassis soldering, Mark, then you may simply not have enough heat to get whatever flux you hae tried fully active. A brute of a soldering iron is needed.... 200W or so.

As plan B a bolted solder lug is a viable alternative, even if not original looking.

If it's wire out of a transformer, then "heavy formvar" varnish doesn't solder through and no flux will touch it that wouldn't destroy the copper. The usual tool is a set of motorised spinning blades which machine off the varnish. This is the varnish for proper serious transformers, designed to run hot and survive.

David
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Old 18th Aug 2022, 11:45 am   #17
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Default Re: 'Spirits of Salts' as soft solder flux?

Quote:
Originally Posted by John M0GLN View Post
Quote:
Originally Posted by mark_in_manc View Post

I guess failing to neutralise the flux leads to corrosion - maybe a little alkali (I have some caustic soda) might be appropriate
Washing Soda which is Sodium Carbonate is much safer to use.

John
It is.

Neutralise a strong acid with a weak alkali - which washing soda is.

Use it to a sensible excess - flood the area - so that you know all the acid is gone. Then all you've got left is the excess of weak alkali, which is relatively benign.

If you use caustic soda, you'd have to use the exact amount (difficult to know!) and also you'd have to be sure there weren't any acid-rich or alkali-rich areas (also difficult). Because, remnants of caustic soda are as corrosive as remnants of hydrochloric acid!
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Old 18th Aug 2022, 8:35 pm   #18
mark_in_manc
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Default Re: 'Spirits of Salts' as soft solder flux?

Great! OK, Washing soda it is. The current task is OT (sorry Joe, I meant 'off topic' not output transformer !) for this forum, but thanks for all your good advice. David's advice of a brute of a soldering iron made me smile, because that is what I used - after my (three!) horrible cheap Chinese mini-butane-torch thingies all packed up, and the oxy-propane setup I have totally refused to stay lit using anything other than a large acetylene nozzle (small ones just go out) resulting in way, way too much heat. Luckily the biggest electric iron I have (a 1" diameter copper bit of unknown power) was just about up to the job (nipples, is all I am saying ).
Thanks again
Mark
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Last edited by mark_in_manc; 18th Aug 2022 at 8:42 pm.
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Old 18th Aug 2022, 9:37 pm   #19
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Default Re: 'Spirits of Salts' as soft solder flux?

AHH!!!, now I know what you are doing!!. Yes killed spirits is the right product to use on those pesky nipples used on conveniences of a velocopedic nature. Wash with plenty of water afterwards. Still requires a 200 watts or so soldering iron. Using a gas flame is much faster but softens the metal in the "wire " and it will break there first. I know, I have persued many items that used those nipples.

Joe

I should also mention, 50:50 solder is required, 60:40 is too soft.

Last edited by joebog1; 18th Aug 2022 at 9:38 pm. Reason: additional information.
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Old 18th Aug 2022, 10:00 pm   #20
60 oldjohn
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Default Re: 'Spirits of Salts' as soft solder flux?

Hi Mark, it is Lead Tin solder you are using? not the lead free stuff. I once picked the wrong stuff off my bench and did not realise for a few minutes. Another thought, the type of copper wire I expect you may be using can go rotten and black, just before it goes black it is very difficult to solder.

Crossed with Joe, if nipples please ignore last comment.

John.
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