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Making Bleach

Little_Ghost_again - 3-10-2015 at 07:58

This is a rerun of the experiment I did making chloroform with IPA, I still cant find answers to some of the observations I had.
So I want to try again and see why things didnt turn out as I expected.
The bleach I have is somewhat degraded but I have alot of it, so my options at the moment are to try and concentrate this bleach or make my own.
As I understand it I can make bleach by bubbling chlorine into dilute sodium hydroxide, is this correct and what kind of concentration of active chlorine can I expect?
Is there anyway to increase the strength of the bleach I have by bubbling chlorine into it?
I am also trying a couple of other things but I will wait and see how they pan out

hyfalcon - 3-10-2015 at 08:13

Use some of that MMO I sent you with close temperature control. One of the side reactions of hypochlorite and I don't remember the temp and charge density it must be run at that favors that side reaction but it shouldn't be to hard to find.

deltaH - 3-10-2015 at 08:14

You're not using electrolysis? If you want to use chlorine gas, then you best add sodium carbonate to the solution, else the pH will become too acidic and you will stop dissolving chlorine. Try to keep the pH just above 12.

Also, make sure the solution doesn't get warm or you will make chlorate. Cool with ice!

ave369 - 3-10-2015 at 08:32

A question for someone who tried making bleach.

How intensely does chlorine react with a concentrated alkali solution? Should I bubble the gas through it very slowly to avoid having unreacted chlorine? Specifically I'm talking about potassium bleach as precursor to potassium ferrate.

Little_Ghost_again - 3-10-2015 at 09:06

Quote: Originally posted by hyfalcon

Use some of that MMO I sent you with close temperature control. One of the side reactions of hypochlorite and I don't remember the temp and charge density it must be run at that favors that side reaction but it shouldn't be to hard to find.

Ah I cant do multiple quotes!!!
I hadnt thought of electrolysis, can you expand on this a little please. I am willing to try several methods, those MMO grids have been great. I cut two small sections off one the larger ones and they still seem to be growing strong! One is now getting a bit darker in colour in colour to the other but still going strong

.
I chose to cut 4cm lengths so I had more if things went wrong.

I dont have sodium carbonate at the moment, I have magnesium carbonate or sodium hydroxide. I might have some sodium Bi carb but will need to go check on that.
I know this will seem pointless but in the IPA experiment I did I added sodium Chloride and sodium Hydroxide when making the chloroform, I am wondering what happens if you saturate the bleach with salt? I have a flask with bleach and salt in at the moment.
I know its not real science but I am trying to find out what actually happened last time
Thank you for the answers

UC235 - 3-10-2015 at 09:30

Chilled sodium or potassium hydroxide solution is very effective at absorbing chlorine gas until you get close to equivalence. It's easiest to track chlorine absorption by weight and with NaOH, 12%ish by weight is a good target. It is very exothermic from what I remember so you'll need quite a lot of ice.

Existing bleach can be made stronger (in fact it will save you a lot of hassle and reagents to do so) by adding cooled conc. NaOH solution and adding chlorine gas until desired weight gain. Heavily degraded bleach might end up saturated or precipitating salt though, so proceed carefully if that is a problem. Addition of salt has basically no effect on bleach and it probably contains a fair bit anyway leftover from the electrolysis brine.

[Edited on 3-10-2015 by UC235]

Little_Ghost_again - 3-10-2015 at 10:01

Quote: Originally posted by UC235

Chilled sodium or potassium hydroxide solution is very effective at absorbing chlorine gas until you get close to equivalence. It's easiest to track chlorine absorption by weight and with NaOH, 12%ish by weight is a good target. It is very exothermic from what I remember so you'll need quite a lot of ice.

Existing bleach can be made stronger (in fact it will save you a lot of hassle and reagents to do so) by adding cooled conc. NaOH solution and adding chlorine gas until desired weight gain. Heavily degraded bleach might end up saturated or precipitating salt though, so proceed carefully if that is a problem. Addition of salt has basically no effect on bleach and it probably contains a fair bit anyway leftover from the electrolysis brine.

[Edited on 3-10-2015 by UC235]

Thanks I will set this up and give it a try.
In case the chlorine generator gets out of hand and at the end of the reaction if I need to get rid of the chlorine will bubbling it into thiosulphate get rid of it? I know thiosulphate neutralizes bleach so I am wondering is a solution of it will get rid of the chlorine?

UC235 - 3-10-2015 at 10:12

Quote: Originally posted by Little_Ghost_again

Quote: Originally posted by UC235

Thiosulfate would work, but the path of least resistance is easiest. Use an inverted funnel over some more dilute NaOH solution as a scrubber.

deltaH - 3-10-2015 at 10:47

Interestingly, chlorine passed through ice cold water precipitates transparent crystals of a chlorine hydrate. According to attached paper, it has an empirical formula of 6Cl2.46H2O.

This is easily reversed and the crystals effervesce chlorine when thawed.

I wonder if the chlorine hydrate can first be prepared by bubbling chlorine straight into a snow/crushed ice slush, decanting, then slowly and carefully adding alkali solution to this with cooling to make a really concentrated bleach.

I see this is something best done in winter

Attachment: chlorine hydrate structure.pdf (701kB)
This file has been downloaded 413 times

[Edited on 3-10-2015 by deltaH]

Little_Ghost_again - 3-10-2015 at 11:17

Quote: Originally posted by UC235

Quote: Originally posted by Little_Ghost_again

Quote: Originally posted by UC235

Thiosulfate would work, but the path of least resistance is easiest. Use an inverted funnel over some more dilute NaOH solution as a scrubber.

Yes a much better idea!! I will be using an aquarium pump to push the chlorine left in the reaction vessel out, as I dont have a fume hood at the moment I was looking for a way to empty the reaction vessel of chlorine, never occurred to me to just make a weak bleach with the excess gas.
Its late now and I have lost the light so will continue this in the morning.
Delta H thats got to be worth a try

, I might give this a go after I have tried the other ways. I have some ice made with sodium chloride I could crush, its reading -18 on the IR thermometer so I might try this, I use milk bottles filled with saturated salt solution then frozen for cooling water in buckets etc, I have several of these so might try this out

deltaH - 3-10-2015 at 11:20

Well the nice thing of first forming the chlorine hydrate is that you knock out the heat of fusion and the hydrate itself melting has a heat of fusion, so all this makes for much better temperature management when you add the NaOH, plus the chlorine is about as concentrated as you could get it, short of working with liquid chlorine.

But be prepared that the hydrate may decide to thermally run away and vent all its chlorine in one go! PRECAUTIONS! PRECAUTIONS! PRECAUTIONS!

A gas mask with ability to absorb chlorine would be a good idea!

[Edited on 3-10-2015 by deltaH]

Little_Ghost_again - 3-10-2015 at 11:38

Just as a side thought, seeing as I have a lot of hydroxide prills and no sodium carbonate, I take it I can just leave some the hydroxide prills out and wait for them to dry out again, i take it this way I should be left with sodium carbonate. Or I guess I could just bubble co2 into prills that have turned liquid in air.

Little_Ghost_again - 3-10-2015 at 11:43

In the morning I will post some pics of my set up, if it looks ok I will give it a go and try for the hydrate. No gas mask but I can do it outside.
I will probably leave some of the ice water with the hydrate and drip the hydroxide into that, it might help with keeping it cool, if I can find a big enough container I will fill that with crushed ice as well

deltaH - 3-10-2015 at 12:03

It's wise to work on a small scale first. I suspect it's not that easy to form the hydrate.

I'd fill a small flask with finely crushed ice and lead in the delivery tube from the chlorine generator and then for good measure, put the ice containing flask in a bucket of ice slurry, but I wouldn't salt it.

I don't know what you're using for a chlorine generator, but I'd use just enough there so that it can be started and then get well away while it's delivering the chlorine. When it's all done, you can approach it again, but make sure the flask is sitting in a bucket of ice slurry at all times, else chlorine will start evolving rapidly!

My gut feeling is that salted ice might mess things up. I'd just work with ice slurry at 0C.

I strongly suggest you try to get a gas mask, even if working outside. It just takes the weight off one's shoulder.

In the second step, I'd slowly add the sodium hydroxide while swirling and cooling in the ice-slurry bucket. This stage is where I think you really need a gas mask because you will be near the chlorine!

If chlorine starts venting, immediately move away far upwind!

I wouldn't use carbonate if using the chlorine hydrates, just sodium hydroxide solution.

You will be targeting a pH of a little over 12 eventually. This is the pH of regular bleach, not sure if it's a good pH for a concentrated bleach?

[Edited on 3-10-2015 by deltaH]

Little_Ghost_again - 3-10-2015 at 12:19

I will have a look and see if I can use an addition funnel and maybe use something like a 3 neck flask. that way if chlorine does evolve it can be scrubbed. I prefer to try and avoid it getting out in the first place

.
The mask i have definitely isnt upto chlorine, I will see what I can rig and if it isnt adequate then I will wait until I can get a mask.
I need another fume cupboard really, but that isnt going to be soon.
I really appreciate the help. The salt bath I will use just for cooling, I will go make some plain ice now so its ready for the morning.

deltaH - 3-10-2015 at 12:27

Working with chlorine hydrates is just a hypothetical alternative, but I love to look for new and possibly better ways to do things. If all else fails, simply bubbling chlorine into chilled alkali will work.

[Edited on 3-10-2015 by deltaH]

Little_Ghost_again - 3-10-2015 at 12:46

Quote: Originally posted by deltaH

Working with chlorine hydrates is just a hypothetical alternative, but I love to look for new and possibly better ways to do things. If all else fails, simply bubbling chlorine into chilled alkali will work.

[Edited on 3-10-2015 by deltaH]

I will try both ways, I use Chloroform for some extractions so finding a way to make stronger bleach or even making a decently strong bleach would be good. No harm in trying it out!!
What is the theoretical limit to the strength of the bleach using hydrates?
If it works the being able to make Chloroform using less liquid makes the whole thing easier, at the moment I use a 15 ltr carboy and pouring off the solution to get to the small amount of chloroform is a bit of a pain.
I am wondering if you could use IPA with sodium hydroxide and then bubble the chlorine in, but thats probably pushing it lol. Contrary to popular belief I do experiment a fair bit, but I am not great at maths and working out formulas I find hard, so I dont post most of the things I do as it makes me look stupid when I cant do the working out and formula stuff.
I also have an update for the iodine thread, I cant get pics until the morning but I had a couple of surprises

Bot0nist - 3-10-2015 at 13:11

Off topic.

LGa, have you tried the haloform using OTC bleach and acetone? A few of us had moderate success in this thread. Is Isopropyl just much easier to find or cheaper to use for you.

Using a 15gal carboy would be hell to cool properly, is that hurting your yeilds. You should post a chloroform writeup, in that thread, or elsewere. I'm curious of the reaction conditions and yeild.

[Edited on 3-10-2015 by Bot0nist]

deltaH - 3-10-2015 at 13:14

Theoretically, let's say you isolate 6Cl2.42H2O and remove all excess water. Then let's say you add 50% sodium hydroxide solution on a weight basis, on a mole basis, that 1 NaOH to 2.2 H2O.

Cl2 + 2NaOH => NaClO + NaCl + H2O

6Cl2.42H2O + 12NaOH + 26.4H2O => 6NaClO + 6NaCl + 284.4H2O

That's 7.5% NaClO on a weight basis... so not that high.

[Edited on 3-10-2015 by deltaH]

Little_Ghost_again - 3-10-2015 at 13:20

Quote: Originally posted by Bot0nist

Off topic.

LGa, have you tried the haloform using OTC bleach and acetone? A few of us had moderate success in this thread. Is Isopropyl just much easier to find or cheaper to use for you.

Using a 15gal carboy would be hell to cool properly, is that hurting your yeilds. You should post a chloroform writeup, in that thread, or elsewere. I'm curious of the reaction conditions and yeild.

[Edited on 3-10-2015 by Bot0nist]

I have a couple of old threads I did on it on here, I will see if I can find them. IPA was what I had at the time and I found very little in the way of temperature rise. I cant remember off hand but I am sure in the thread I noted it was only 3 or 4c rise (I think???).
This thread is actually about another attempt at making Chloroform with IPA, last time I observed a few things I just couldnt understand as i added salt and sodium hydroxide and didnt measure much, this time I want to do it and measure everything. I used IPA because I had alot of it at the time, looking at others yield maybe mine wasnt so bad after all. One thing for sure if I had removed the Chloroform earlier then I would have had much more, it wasnt the temperature I think it was the amount of sodium hydroxide I added.
But bare with me this thread will turn into a chloroform write up, I am trying first to see if I can increase my bleach strength. The bleach I got was 20 ltr but its sat for a while and seeing as it cost me £21 I want to use it

Little_Ghost_again - 3-10-2015 at 13:44

one of the other chloroform threads I did was this one http://www.sciencemadness.org/talk/viewthread.php?tid=33930
its crap and I am sure I messed up the temperatures, looking back aga was right about the IR thermometers, so I wouldnt rely on the temps I gave. what I can tell you is the solution barely got warm, certainly less warm than I normally get mixing hydroxide with water, but that itself seems a bit odd. Anyway this attempt will be documented better, i am interested in one of the by products i got because i couldnt find out what it was.
It proved to be a great solvent though

hyfalcon - 3-10-2015 at 17:58

Download the pdf at the bottom of the thread LG. Good read.

http://www.sciencemadness.org/talk/viewthread.php?tid=43266

AJKOER - 3-10-2015 at 19:13

Here is a form of solid bleach from one of my prior threads, "Preparation/Exploration of Mg(ClO)2.2Mg(OH)2, a Solid Hypochlorite", at https://www.sciencemadness.org/whisper/viewthread.php?tid=26... that you may find of value.

Not strong enough? You may try treating the moist compound with chlorine (which I have not tried) with the intended goal of the monobasic magnesium hypochlorite, sometimes described as Mg(OH)OCl, as the pure magnesium hypochlorite apparently does not exist (see, for example, discussion at https://en.m.wikipedia.org/wiki/Hypochlorite .

[Edited on 4-10-2015 by AJKOER]

Little_Ghost_again - 4-10-2015 at 02:26

Thanks I will start reading, not had a great start this morning, suggestions for chlorine generation? I would prefer a solid and drip a liquid onto it, guess which one I have tried so far

. 7.5% is less than I can buy, I would like to aim for 15%+ is that going to be possible? Having said that if I add the hydrate to the bleach then maybe it will help as the bleach is used up. I better go read instead of just guessing.

Little_Ghost_again - 4-10-2015 at 02:40

Quote: Originally posted by hyfalcon

Download the pdf at the bottom of the thread LG. Good read.

http://www.sciencemadness.org/talk/viewthread.php?tid=43266

that is a good read, I will get bogged down if I try too much at once. So plan is to stick to the hydrate first, then try the others one by one using IPA. I figure we should find a decent way to make chloroform with IPA and a way to make the bleach strong. Yes I know people use acetone but I did have some good results with IPA and I would like to see where it goes.

deltaH - 4-10-2015 at 03:32

I may well have goofed up the calculation, so feel free to check it, but the problem is that the hydrate has a lot of water intrinsically associated with it. There also seems to be some confusion as to what the empirical formula of the hydrate should be, different sources give different ratio's. I trust the one I used a little more because it came from a paper which determined it's crystal structure from XRD.

Little_Ghost_again - 4-10-2015 at 04:00

Thats ok Delta H, I dont have a clue yet how to work these things out, but I am trying to learn. I want to try as many methods as I can, so it dosnt matter too much about yield. I am more interested in seeing if any of the bleach making methods improve chloroform with IPA and if/what side products are made.
Rain has stopped play for the moment, I dont fancy having have electrical stuff outside in the pouring rain

, but it gives me a chance to read some the pdfs posted

Bot0nist - 4-10-2015 at 04:18

TCCA has been praised as a great and efficient material for use in a chlorine generator. A quick search of the forum should provide countless discussions and setups. IIRC, woelen dished out some great advice and experience about it in a couple places. As always, UTFSE, and be safe. As I'm sure you know no, making large amounts of chlorine can be a bit troublesome for your, and others help.

Good luck, and keep us posted.

Little_Ghost_again - 4-10-2015 at 04:29

excuse the ignorance is TCCA Trichloroisocyanuric acid? I dont have any if it is.

Little_Ghost_again - 4-10-2015 at 04:36

Safety could be an issue, so major glass cleaning operation while the rain is bad! I intend to try and keep things as closed as I can, might be overkill but with limited equipment I figure glass rods and any joins done with PTFE wrapped over the joins and held tight in place with heat shrink tubing.
Dropping funnels and 3 neck flasks, 3 way glass valve so if needed I can dump excess chlorine to thiosulphate was bottle, its new and has a glass frit so i didnt fancy using hydroxide in it for the first outing lol.
Aquarium air pump to push any excess chlorine from generator into wash bottle, I havnt figured the ice slush yet but probably crystals in a flak and a drop funnel for adding the hydroxide, 3 neck again to wash bottle if chlorine is evolved and gets out of hand.
I will also set up a mini chloroform run the way i tried before and this time try and weigh things more accurately, i have a good temp data logger I can leave on the side of the flask and track the temperature over night.

Little_Ghost_again - 4-10-2015 at 07:04

Unfortunately Trichloroisocyanuric acid is pool shock? I live in Scotland and I doubt there is more than 2 home pools in the whole of Scotland!! Apart from living in a very rural area I think it likely only one or two cities here would even have a pool supply shop.
I will look online and see how much ebay wants to fleece me for some, failing that anyone got any other ideas for producing chlorine?
Looks like potassium permanganate and hydrochloric acid, I could clean up some manganese dioxide from some of the old cells I have but I dont trust the contaminants.
This is a real PITA, I was hoping to have a easy way with what I had at home, I would use electrolysis but that means making something to stick the electrodes through so I can seal the container.
Anyway lunch is over the parents are out and the kitchen is free

, so best I catch up on the glassware cleaning.

[Edited on 4-10-2015 by Little_Ghost_again]

Bot0nist - 4-10-2015 at 08:54

Sorry, I took for granted that TCCA is readily available and cheap in my area. A few pool shock pucks of TCCA could probably be had cheaply online. I have seen them in little foil packets. Or get a 5 gallon bucket of the powder if you need a lot of chlorine.

Little_Ghost_again - 4-10-2015 at 09:43

1kg is about £16, not too bad but cleaning up battery gunk is free (ish) and I have 7ltr conc hydrochloric acid. I also have permanganate.
Its a tough one because I have a limited budget but then again I want to give this a good shot. if I can find a way to make the container then electrolysis of Brine would seem the best way. Wikipedia dosnt mention oxygen being off at the Anode but other sources mention it.
I didnt get to do much today, I had a great deal of backed up glassware and still more to clean. Since being banned from the kitchen I have got lazy with cleaning, I also dont have hot water in the outbuilding I have been kicked out into.
I confess with some of the thicker walled really dirty glassware I washed out best I could then added water and some sodium hydroxide, instant hot water lol, its cleaned the glass nicely.
I didnt leave the solution in very long though. I am going to read all the info I have been given before going further, I really want to get this right. I found a 2 ltr flask with the waste from a chloroform run, I used alot of IPA and the top layer smelled like a solvent but not IPA or acetone.
Now it smells closer to acetone, I will distill it and see what the boiling point is. I also found a few bits of glassware in a box that I have no idea what they are for, I might post pics later and see if anyone has any idea what they are.
Thanks for the help, its really appreciated. I doubt anyone is going to take it seriously but the very first run of chloroform I did with IPA bleach,salt and sodium hydroxide worked really well and I started at room temp, I didnt get very hot temps and I think most of that was actually from the hydroxide.
This time I will document it, the bleach is kind of a side project from that.

I can do much as its getting dark but I might try and draw what I have in mind, I did think sulphuric acid and salt would give me chlorine but that didnt work too well

[Edited on 4-10-2015 by Little_Ghost_again]

Little_Ghost_again - 4-10-2015 at 14:29

I started reading the PDF and the bit near the start where it talks about absorbing chlorine gas into dry calcium hydroxide caught my eye, it says upto 70% chlorine is possible, I doubt I would go anywhere near that and I dont have calcium hydroxide. BUT in the back of my shed from long ago is an old 10 ltr carboy with hydrochloric acid in and dissolved seashells, I was making calium chloride that I then reacted with sulphuric to get calcium sulphate.
To be honest I forgot all about it until tonight.
I then found this video online https://www.youtube.com/watch?v=MdIHl2JnD-I
In it the guy makes calcium hydroxide by reacting calcium chloride with sodium hydroxide, I have a shed load of sodium hydroxide as I make soap. My calcium chloride is a bit erm rough, the pics make the vessel look small but I had to take the picture with a lamp as the container is in a shed with no light.

It dosnt look like it but the white powder under the dirty layer is very white, the solution still dissolves sea shells so I assume its still pretty acidic. Now its all settled out I could hoover out the dirty layer with a large glass tube connected to a vessel and vacuum pump, then hoover some of the clean powder and wash it.
From that I could mix with sodium hydroxide and get my calcium hydroxide?
Its hard to tell from those pics but there is a fair bit of powder in there, also if I drip some of the liquid into sulphuric acid I get a white precipitate form, so I am assuming I do actually have calcium chloride in the main vessel.
Thoughts welcome as always.
The bit I got it from in the PDF in this thread says the following about it....
In 1799 C. Tennant and C. McIntosh developed a process for the production of bleaching powder by absorbing chlorine onto dry calcium hydroxide. This bleaching powder was
much more stable than previously obtained
bleaching products. In 1906, G. Pistor succeeded in producing highly concentrated bleach-ing powder with more than 70 % available chlorine.

It dosnt say exactly how you get the powder to absorb but I havnt read it all yet. in some ways this would seem safer, but I dont want to go too far as obviously making chloroform with it for the first time will be small scale.

Just as a side note the shells were mainly razor clams and had alot of organic crap around them, I heated the shells in a pan on a open fire to try and heat alot of it off. Thats where I think the dirty layer comes from, the powder thats white settled pretty quickly after fizzing and left a dirty solution, but over time the solution has cleared alot and the fine crap layer has settled on top

[Edited on 4-10-2015 by Little_Ghost_again]

hyfalcon - 4-10-2015 at 14:39

Do you have access to pickling lime? If so, you have calcium hydroxide, or calcium oxide which upon adding to water...

Little_Ghost_again - 4-10-2015 at 15:02

Quote: Originally posted by hyfalcon

Do you have access to pickling lime? If so, you have calcium hydroxide, or calcium oxide which upon adding to water...

Never heard of it but a trip to the super market will reveal if we can get it

. If not do you think the method I outlined above will work?
I know its a long route but in case I cant get the pickling lime....
I might ask mum about it she would know if pickling lime was in the shops, she does pickling and stuff like that
I know the pics look grotty but the dirty layer is very thin, I can definitely suck up some the white powder and wash it? Oh it just occurred to me I better see how soluble it is in water!!! If washing is a problem then maybe drying by heating it? the HCL should decompose first shouldnt it?

[Edited on 4-10-2015 by Little_Ghost_again]

Thanks guys I am really having fun with this

[Edited on 4-10-2015 by Little_Ghost_again]

Little_Ghost_again - 6-10-2015 at 13:57

Ok no end of problems!! I need some different tubing for a start, we have two weeks off starting next week so..
The plan is two do small scale Chloroform using IPA and a few variables of the method I used, I will use the bleach I have at the moment and order some better tubing for the chlorine, if this comes in time I will re run with the new bleach I make.
I thought this would be easier than its proved to be!

aga - 6-10-2015 at 14:12

With charcoal, a short length of steel pipe (fence post) and a hairdryer you can get up to some insane temperatures (1500C ?) albeit briefy.

It's messy as the airflow blows crap all over the place, however i've seen this simple setup melt about 30g of Steel easily.

I was trying to melt copper in a steel pot at the time.

The copper may have alloyed with the steel, lowering the melting point (depressed eutectic !) or something like that - i do not know.

The Copper certainly melted, so that's 1085 C right there, and there was a big hole in the steel pot where it;s metal used to be.

Little_Ghost_again - 6-10-2015 at 14:38

Not sure what went wrong but one of the plastic aquarium airlines just went black and started to leak, so better tubing or the chlorine is going to get out. My little oven based on charcoal gets pretty hot, a bit like yours but I use a small bouncy castle fan for the air flow.

Little_Ghost_again - 10-10-2015 at 08:03

Quote: Originally posted by UC235

I mentioned somewhere or rather asked about adding salt.
I originally added salt when making chloroform from IPA, I think the original idea was to see if I could salt out any water from the IPA or bleach.

The information given back was adding salt dosnt do anything. Because the whole point of doing all this is to see what happened when I made chloroform with IPA I decided to add salt to IPA and in another flask add salt to bleach.

The flask with bleach I added enough salt to saturate and leave a very fine layer on the bottom of the flask, nothing weighed as this was merely a lets see what happens thing.
This was a couple of weeks ago now and for the first week nada, nothing, no change. Then starting yesterday I noticed that the top of the flask 'MAY' be a lighter colour, this is very subjective at the moment and the difference is very tiny.

Whats interested me is there are definite vey very tiny bubbles on the top of the salt crystals, these bubbles are evolving at a slow rate and so far I would say most of the top of the salt layer has these very tiny bubbles.
The flask has been sealed all this time with bubble wrap, upon taking of the bubble wrap the smell of bleach is less. But that makes me think that maybe this is down to the lighter coloured layer (if it exists).

Now I know there is probaly a reasonable explanation for this but the number of these tiny bubbles makes me wonder what is going on