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peach
Bon Vivant
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Hmmmm
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blogfast25
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Quote: Originally posted by not_important  | | I'd like to see references for that. From what I've read the main sources are byproduct HCl from chlorination of organics (which contains iron from
attack on the pipes and so on), from burning H2 and Cl2 from electrolytic production of NaOH, from controlled incineration of chlorine-containing
organic waste. |
I don’t have any, not_important, I was merely going by the fact that nearly all HCl I’ve ever bought is yellow coloured (demonstably by Fe3+), I
didn’t realise they carried on that tradition with by product HCl! 
| Quote: Originally posted by peach | You could try a silicone stopper instead, or painting silicone caulk over the whetted surface of the natural rubber. You could even bed PTFE tape over
the silicone before it cures.
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Hmmm… silicone is about the worst choice you can make: it’s hydrolysed very quickly by wet HCl, as witnessed in my tests linked to above. At that
time I only had silicone tubing and used it for that set up. After about two runs the silicone had turned basically to SiO2 and had to be replaced!
It would probably resist a lot better to perfectly dry HCl.
[Edited on 25-1-2011 by blogfast25]
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Arthur Dent
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What would be the best tubing material for HCl gas and/or Cl ?
Teflon would be best ideally but I shudder just at the thought of the cost of teflon tubing. How about black neoprene? Would the orange rubber stuff
be any good?
I have a lot of transparent PVC tubing but I must admit I have never used it for HCL / Cl gas. I've seen the pictures of what bromine does to that
kind of tubing (turning it opaque red), and before attempting an experiment with HCl gas or Chlorine, I want to make sure my vessels are connected
safely together...
Robert
[Edited on 25-1-2011 by Arthur Dent]
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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entropy51
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I don't know what would be best, but the generic clear plastic tubing from the hardware store works just
fine. It will eventually deteriorate, but not after a single exposure, in my experience. In the distant past I even used rubber stoppers on my HCl
generator, but since I have ground glass now I use that instead. I've tried other ways, but I still like the inverted funnel for HCl absorption.
Cool the absorber in ice water if making strong HCl.
I do think that it is necessary to heat the HCl generator to obtain a decent yield of HCl. I add the H2SO4 dropwise from an addition funnel and then
heat it when gas production slackens.
When NOT making anhydrous HCl gas I find that adding just a little water to the NaCl helps to reduce the foaming that occurs when the sulfuric is
added dropwise. Coarse NaCl in lumps seems to foam less than finely ground table salt.
I dislike using CaCl2 instead of NaCl because I don't like to let CaSO4 (or any insoluble solid) go down my drains. I neutralize the slag left in the
generator with Na2CO3 before flusing it down the drain.
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blogfast25
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Robert:
Neoprene, PVC, EPDM (ethylene propylene copolymer elastomers) are all good. NR will degrade quite quickly but not immediately. None will last forever
but most of these for quite a while. Teflon is serious overkill for HCl… Even cheaper fluoropolymers like Viton elastomers aren't needed by a long
shot.
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peach
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Teflon tubing is not only expensive, it is not easy to make connections with due to it being a rigid polymer, as opposed to an elastometer, and not
particularly flexible by comparison. This problem is only made worse by the fact it won't thermoform (that is such a bitch!), so you can't easily melt
connections together - as they do with the underground mains pipes in the road.
I have used fluoroelastomer tubing with HCl(g) before. When combined with halogenated solvents, it too can turn opaque, but the mechanical properties
of the tubing don't change.
I have been playing around the last few days building a generator out of HDPE bottles, hydroponic fittings and, what I suspect to be neoprene, tubing
- using concentrated sulphuric onto table salt.
Test number one was a failure in terms of getting clean hydrogen chloride out of it.
I drilled the holes for the little barbs dead on - they were 5.3mm in size according to the micrometer, so I chose a 5mm bit for a push fit. I then
siliconed the barbs as they went in, to try and get a gas tight seal around them - letting it cure overnight.
All seemed to be going to plan, until fixing the tubing and filling it came to fruition. For a start, the silicon bond to the smooth caps on the
bottles was not great. Trying to push on the, now fairly rigid, tubing (having been out in the garage at 4C) caused the seal on the top bottle to
start peeling away as I wiggled it. I thought... oh well, it's probably still plugged well enough inside the hole. And, it didn't matter anyway, given
what happened next.
On filling the top bottle with the sulphuric, the silicone seal utterly failed - within seconds it was peeling apart.
In addition to that, I was trying to think of an easy way to control the flow rate, and had tried bending the tubing over on it's self and clamping it
with one of the free arms on the retort. Again, with the tubing being so dense and cold, it obviously hadn't cut it off anywhere near well enough, as
the acid drained far too quickly into the salt. With the bottles being tall and thin, the salt foamed and went over into the water I was using to
collect the gas.
Rather than simply hose the entire thing down and bin it, I am leaving it alone to finish, as it can still provide useful feedback on how compatible
the other components are given that they're now exposed to the salt, concentrated acid and hydrogen chloride.
I seem to recall sauron saying PVC will ignite in the presence of hydrogen chloride. I'm not sure about that, as I've never seen it do it and the cole
parmer resistance guide actually rates it A for compatibility - maybe that was a joke that passed me by. It rates it as A, excellent, for all
sulphuric acid up to 75%, then D, severe, for anything above. As with everything science and engineering related - TEST IT YOURSELF
In terms of neoprene, again, a D for concentrated sulphuric. I've just been dipping a length of it (or what I assume to be a length of it) in
sulphuric and not seen any problems. There is no data available for hydrogen chloride. I have used it with hydrogen chloride a number of times before
and not seen any immediate problems - it did have a major problem when it was also in contact with DCM.
You can only buy into the resistance guides so much. They are VERY broadly speaking and heavily application dependant. For example, a piece of tubing
that is constantly being flexed in an aeroplane's wings and that needs to last for a decade supplying fuel to the engines is much more of a problem
than a piece that's going be exposed for a few hours, not manipulated and then rinsed - or possibly binned after ten or so goes doing an experiment in
the garden. You will also note that every single resistance guide you find will say "These are approximations and our experiences, we assume no
responsibility, check it yourself, lazy"
Whilst this attempt has entirely died on it's arse, I'm not all that bothered as there are things I can note about this that could lead to being able
to do a lot better with another go. I also don't need the resulting gas or hydrochloric.
The goal was to see if the far harder to break and cheaper plastics could be used over glass. If a compatible setup is found, you could scale this up
and run it in 1/ 2 / 5 / 25l HDPE containers. That would be useful for producing larger quantities of anhydrous salt or for drying such salts.
I need to have another look at the plastics once it's had time to sit out there and stew, I'll leave it overnight I expect.
But, the observations thus far!
1.) The HDPE doesn't seem to care. I have so many chemicals turn up in HDPE - including 34% hydrochloric and concentrated sulphuric. Before I check
the bottles outside, I can be almost certain the HDPE will be fine, as it's fine when it turns up in bottles made of the same polymer. This in line
with Cole Parmer's guide, listing even LDPE as fine for the sulphuric and hydrogen chloride.
2.) Crimping the tubing is not an excellent method of controlling it, unless you're using a fine control clamp, and one that's light enough it's not
going to pull on the tubing
3.) Coloured drain acid is good because the HDPE is opaque, making the bright pink / red stand out well
4.) DO NOT bother with silicone anywhere that it will come into contact with the sulphuric. Silicone tubing will likely go the same way. I would go
further and suggest you don't use it at all, as you'll probably end up with the acid on it at some point and then be wondering why the generator
isn't working, but everything around you is rusting.
5.) Rather than crimping and clamping the tubing, one could use a PE or PP stop cock, as is used on garden watering system, wine siphons, jerry cans
and so on
6.) Do away with barbs and use screw in fittings
7.) You could consider using either HDPE or Polypropylene tubing in place of PVC and neoprene, as both the formers are more resistant to what's
happening. Like Teflon, however, they tend to be rigid. Unlike Teflon, they are thermoformable; you can melt connections together.
About as successful as my attempts to woo Kelly Brook by hiding in her garden every night
I removed the equalising tube and stuck that in the water as well, after realising this wasn't going to work and watching the salt bottle foam up.
Even with that tube gone and the barb being a tight fit, there was sulphuric dripping out around the fitting on the top bottle where the silicone had
previously been. You can see the acid on the green plastic bin it's sat on; look between the front right of the clamp stands base and the volumetric
flask
The main offender - silicone, sliding off like an egg on a greased up frying pan
Does anyone remember the kid's TV show called "It'll never work". Well, that's never going to work. But the bottle and plastic barb don't seem
to mind, or the (probably) neoprene tubing. The place I bought the tubing from didn't say what it was, but that spongy, shiny surface looks
familiar
Crimping over the tubing didn't block the tubing off anywhere close to how well it should be. I don't think this is a stellar method, using
any form of clamp, crimp, adjustable pliers and so on, as they tend to be for on / off control and struggle to do it finely; more so when the tubing
is tough (they can get significantly more rigid with changes in the weather). It would be better with an actual stop cock there (check online garden /
pet / fishy stores)
The silicone on the lower bottle is a liar. Because it wasn't subject to much movement and wasn't in direct contact with the sulphuric, it's
pretending it'll be okay.
Even though the pile of salt in the bottom isn't taking up much room, you can see the water in the collection flask is pink, from it foaming.
The foaming would be less of a problem if most of the acid hadn't drained through in a minute or two. I would also suggestion caution if you're going
to have a go at doing this without any previous experience making the gases in glassware, and dealing with them, as something at these early stages of
testing fittings could potentially clog and then pop - blowing the acid all over you and the inside of your house, along with releasing a decent
quantity of hydrogen chloride. You certainly wouldn't want to start testing your ideas by generating ten moles of something very toxic or flammable -
e.g. hydrogen sulphide, acetylene, monoxide, hydrogen cyanide...
Concluderoodo
I was quite pleased with it personally. I think there's potential there.
I'm sure I saw a plastic stop tap in the house that was PP.
Plumbing fittings are PEX and PB. PEX is cross linked HDPE. And you can also get pushfit PEX pipe. The only problem could be the rubber seals in them.
The only way to find out is to try breaking one. 
Hmmmmm^2
---> Opens catalogues
[Edited on 27-1-2011 by peach]
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blogfast25
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To try and prevent foaming you might want to try adding some mineral oil.
I also wonder if rate of evolution could be better controlled by using a slurry of saturated brine (36 g NaCl/100 g water) mixed with the same amount
(say about 36 g) of finely crushed NaCl. It should be much easier to mix the acid with the salt slurry than with dry salt.
Silicone? Forget it. Hydrolyses like mad and bonds very poorly, especially to non-polar substrates like most plastics. If you really want to try some
‘poor man’s’ bonding/sealing system, try contact glue. Real contact glue (the stringy, pale yellow stuff that stinks of chlorinated solvents) is
based on high crystalline polychloroprene (CR, aka Neoprene). CR resists most acids well but the high crystalline CR isn’t very flexible (but it is
very tough – high tensile strength). And CR based glues are usually formulated for a wide field of bonding applications, although PE probably
isn’t one of them. I used that quite successfully in the past to cobble together a CO2 generator from non-lab glassware and brass tubing, as a
sealant. Not perfect but just about did the job...
But for the drop funnel for the acid, I really think people should invest in a proper glass drop funnel or separating funnel: not much point having
your acid drip all over your apparatus and fingers, real messy and hard to clean up. For those who just want to make hydrochloric acid solution (the
rate then isn’t very important) adding all acid at once without drop funnel probably works (it did for me).
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peach
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Submitted to Barclays PLC for consideration of loan approval to Mr John
S2 = You'll want a hole in the top of the upper bottle to equalise the pressure between the two. Having a hole in both the top and bottom makes
filling it with concentrated acid, not easy. Hence, a stop tap here to close it off when filling.
S1 = Start the acid flowing
T = Rather than drill yet more holes into the bottles, I'd prefer to keep all of the connections in the caps, with those being thick and rigid. There
is only so much space on the caps, fewer holes means not only means fewer sealing problems on the bottles but more chance of being able to fit the
fitting on there in the first place. I am, therefore, considering taking the gas off from the same connection that equalises the bottle pressures.
Tubing to floating plastic fittings is usually a lot more durable than tubing to rigid plastic to wonky, thin plastic
G = I also considered not making any holes anywhere other than the caps, by having the pressure equalising tube go up through the top bottle cap.
Problem! 1.) needs a double sided connection 2.) will 100% ruin your work if the connection comes loose inside or the tube gets sulphuric in it
W = An optional dry bottle. Would also serve to catch and mistakes if option G was used. However, even with W in place, if G failed, you would still
have to refill the generator. Decisions, decisions!
Addendum
I am thinking it may be best to avoid using plastic plumbing fittings.
1.) They have rubber seals, as mentioned above - possibly not a problem
2.) The smallest bore they come in is 10mm, and the 10mm range doesn't usually have many components available for it. The next up is 15mm, which is
starting to get big
3.) The pipe is so rigid it's annoying to bend. If the generator wasn't fixed rigidly together, any knock or misalignment would stress the connections
to the bottles, and likely open them
Why not get that HDPE Kipp's Generator Mossydie linked to?
That is an AWESOME deal. The whole thing is HDPE and done for you.
However, it also has a fixed volume, and you will tend to be using dilute acids with one given the large volumes needed.
This method would allow you to use both concentrated acids - for maximum space saving - and very large containers, if you like it so phat it needs
spelling with a p.
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peach
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| Quote: | | To try and prevent foaming you might want to try adding some mineral oil. |
Will give it a go. Foaming hasn't been a problem when I've been adding the acid carefully. But, if it helps, it's worth a try.
| Quote: | | I also wonder if rate of evolution could be better controlled by using a slurry of saturated brine (36 g NaCl/100 g water) mixed with the same amount
(say about 36 g) of finely crushed NaCl. It should be much easier to mix the acid with the salt slurry than with dry salt. |
Given the massive solubility of hydrogen chloride in water, using water in the generator is likely going to reduce the yield by a decent amount. I
thought I was being Ghetto by not suggesting people redistill the acid to 98% and then bake their salt in the oven. 
| Quote: | | If you really want to try some ‘poor man’s’ bonding/sealing system, try contact glue. Real contact glue (the stringy, pale yellow stuff that
stinks of chlorinated solvents) is based on high crystalline polychloroprene (CR, aka Neoprene). CR resists most acids well but the high crystalline
CR isn’t very flexible (but it is very tough – high tensile strength). And CR based glues are usually formulated for a wide field of bonding
applications, although PE probably isn’t one of them. I used that quite successfully in the past to cobble together a CO2 generator from non-lab
glassware and brass tubing, as a sealant. Not perfect but just about did the job... |
There's a tube of that in the plastic bag in the picture above, where I have the bits on the surface in the kitchen. Like.... bummer, dude!
But I wouldn't have considered it had you not mentioned what it is. I have a bin full of glues, sealants and caulks - literally tens and tens of them
all the way up to epoxy anchor cartridges. Some of the newer glues, like StixAll, Sticks Like Sh1t, Pink Grip and so on use novel polymer systems
which may be possible options. I bought all of them thinking I'd do a head to head review.
There's also epoxy, no idea right now precisely how well that'll fair.
I chose silicone for the initial test as I've not noticed it doing much when I clean the work surface with sulphuric. I was also thinking, there'll be
guys in Australia, the US, Mexico, Africa, Russia and all over the place who might want to try this. By using some UK only brand of glue, it'd mean
they'd then have to start testing the seals themselves, again. Silicone seemed like a universally available option, and something people might even
have in the garage already. As we have seen, it's not even close to acceptable for this.
A better option is to forget the glues and either melt the plastics together or use screw together fittings with sealing washers.
| Quote: | | But for the drop funnel for the acid, I really think people should invest in a proper glass drop funnel or separating funnel: not much point having
your acid drip all over your apparatus and fingers, real messy and hard to clean up. |
I'd have to disagree there, armed with four glass equalising funnels ranging from half a litre down to 25ml.
Glass is the universal standard for laboratories, and this plastic 'funnel' has entirely failed in this example. However, it's only failed due to the
silicone. For the cost of experimenting with a few different methods and plastics, I think it would benefit many of the people here who can't afford
that kind of glass.
I'd use the plastic method if it works, saving the glass for things that really need high purity or for use with solvents that will
leech plastics.
[Edited on 27-1-2011 by peach]
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blogfast25
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Well, I'd consider the plastic bottle method too (of course) but it still isn’t clear to me what bonding/sealing solution you have for the bit
between ‘G’ and ‘S1’…
Re the solubility of HCl in water and consequent losses of hydrogen chloride gas to water in the generator, don’t forget the saturated brine
solution is approximately 6 M in Cl- and will stay that way because without serious heating you only get the first displacement, so the rest of the
(solid) salt replenishes the solution. Is HCl equally soluble in conc. NaCl? Or will it salt out the salt?
My own tests, using dry NaCl and 94.5 w% H2SO4 yielded only about 50 %, based on NaCl + H2SO4 === > NaHSO4 + HCl. Much of that poor yield was due
to the visible fact that much of the salt hadn’t even seen acid due to poor mixing!
So whilst I haven’t tried this, what I’m hoping is that better mixing and contact between salt and acid would amply offset any loss of HCl as
solution in the generator.
The ratio of brine/solid salt is of course not set in stone: higher salt content may still result in better mixing, only experiment can show that...
[Edited on 27-1-2011 by blogfast25]
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watson.fawkes
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| Quote: Originally posted by peach | | A better option is to forget the glues and either melt the plastics together or use screw together fittings with sealing washers.
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If you're using polyethylene in any of its forms, plan on heat fusion for joining it. You can get plastic
welding rods in PE for filler material. A good adjustable heat gun with a fine enough output tube (perhaps self-made) is adequate. No need for a
purpose-built plastic welder unless you're doing a lot of it; there the ergonomics matter more.
As for fusing barb fittings, I imagine that a small jig could be constructed with a piece of drill rod down the center so that you could get the
fitting hot without too badly deforming the inner diameter.
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blogfast25
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Yep, that reminds me of hot melt adhesives based on thermoplastic Styrene Butadiene Styrene (SBS) block copolymer elastomers: MP just about 100 C
(IIRW), very strong, good bonders and gun applicable...
[Edited on 27-1-2011 by blogfast25]
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peach
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The hot method is perfect in terms of keeping the number of materials down. I was hoping to find a 'squeeze it out the tube' solution for others to
repeat, but I'd be perfectly willing to try melting it. I wonder how a hot glue gun likes having HDPE rods stuffed into it.
In terms of the mixing, when you generated it, could you actually see white salt left in the generator?
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blogfast25
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| Quote: Originally posted by peach | The hot method is perfect in terms of keeping the number of materials down. I was hoping to find a 'squeeze it out the tube' solution for others to
repeat, but I'd be perfectly willing to try melting it. I wonder how a hot glue gun likes having HDPE rods stuffed into it.
In terms of the mixing, when you generated it, could you actually see white salt left in the generator? |
SBS is much, much better as a hot melt adhesive, it is in fact THE hot melt adhesive of choice. The gun and SBS rods are dirt cheap, I picked one up
from a charity shop years ago and forgot all about it! It will now get a new lease on life. SBS is a fascinating material that can be thermo moulded
into artefacts with hugely varying hardnesses, always with high durability. Formulated with tackyfiers and such like it's a very versatile 'glue'
which 'dries' to a tough, highly flexible, fatigue and chemically resistant bond/seal. Try it!
Salt left in the generator? Yes, lots, why?
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peach
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SBS, I'm used to painting it on the walls prior to plastering, rendering and tiling.
I should have said, dry unreacted salt. I tend to add the amount of salt I want then slightly more acid than is needed. It can take an hour or more
for it to get through quite a small pile of it. I have seen generators still producing fumes days later - albeit lots slower than
they initially were. Obviously, that's only the visible material around the sides of the glass as well, and liquids tend to go for the sides first (in
fact, many things do - e.g. people standing by the walls of an entrance to a football stadium get in faster than those standing directly in front of
it, due to a constriction of the axes they can move on).
This (long delay and tapering off in production) is likely why guys who make large quantities of drugs love hydrogen chloride cylinders so much
they're willing to DIY a half cylinder half generator bastard child version using salt cakes, empty propane tanks and blow torches - to get a constant
stream of it on tap.
I have read around that a fair bit, including a police report on them which included many photos, descriptions, one they built themselves and methods
for getting rid of them. Whilst the pressure they can build up is not extreme, the pressure in combination with the ad hock mix of materials and
highly corrosive gas is (for certain) not something I would encourage people to do.
I've just ordered a new pH probe. Once that turns up, I'll be able to provide some pretty graphs of temperature and pH from the generators.
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peach
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Attempt, two
This time I'll be using some PVC tubing and these little HDPE taps
Leaving a sample of the tubing in some concentrated sulphuric overnight
The tubing was tan / brown / amber by the morning, and would later go opaque when rinsed. However, the tubing has not become brittle to my hands
Neither has it's wall thickness changed by any sizeable quantity. I decided to try PVC since it's so easily available and transparent, so I can see
what's going on as I test this
This is the last generator, which has been sat outside since I posted the pictures of it above. You can see unreacted salt, despite there being an
excess of sulphuric. Likely as a result of so much of the acid ending up outside the bottles. There are still faint fumes licking out of the opening.
I tried to photograph them, but they weren't playing
The resulting cake, not budging after three rinses with cold water and me squeezing the bottle. It is from a NaCl generator. The cake did later break
up when I filled the bottle with some hot tap water and gave it another squeeze
Mmmmmmm, cake
Washing the first generator out, I see no signs of wear and tear on the bottles, tubing, cap liners or fittings
I'm going to try melting the fittings into place with a hot pin first, practising on the first generators caps and fittings. I have been using arc and
gas welders since I was 13 or 14, and soldering things since before my teens. But plastic ain't metal
The first attempt, I only did the edges of the fitting and it broke away with little effort. I then put more effort into blending the fitting into the
base material of the cap and got a better result
I purposefully set about trying to snap the fittings, to see how well they'd bonded 8^o
The hot pin method wasn't exactly great, so I tried the soldering iron and hey presto, it works beautifully. Despite having zero temperature control
and costing about £3. I've stuck a bit of copper wire in the end but later switched it to an old tip instead. This is a 40w iron. The temperature is
just high enough to get the plastic flowing, not high enough to instantly cut through it and not high enough to easily burn it
The third ever intentional plastic weld I've made in my life
Bingo! The fitting has snapped before the bond. Mission complete!
The finished bit of tubing. I decided to have the equalising tube come up through the cap and a bit of tubing inside the bottle because I wasn't at
all happy with the bond it was making onto the base of the top bottle. I was worried a lot of sulphuric would end up in the equalising tube as I
turned the top bottle upside down to drain, and so put a tap on there. I found this worked perfectly well, there was no sign of acid in the gas line
once the bottle was flipped
Not pretty, but not presently the point
I've removed the cap liners so I could melt the fittings and caps together on the inside as well. Which means I will need to wrap the threads in PTFE.
Good job I remembered that seconds before turning the bottle upside down.
Everything is looking good! Been for dinner, no leaks!
The taps are controlling the acid brilliantly. It's held it at that position for the fifteen or twenty minutes I've been away
Oooooooo! Close, but not yet! Everything is fine, but it looks like that tap had a rubber seal in it, which is now toast. I've again set the generator
outside and, once it's calmed down, I'll snap open that tap and have a look. Again, I should point out, the rest of the fittings are absolutely sound.
The only leak is from the seat of the tap it's self. The tubing isn't going to fall off those connections easily, it's ID is about 2mm smaller than
the barbs and I had to force it on after a dunk in boiling water
[Edited on 31-1-2011 by peach]
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Melgar
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| Quote: Originally posted by blogfast25 | | Hmmm… much of the world’s hydrochloric acid sloshing around is still produced by heating conc. H2SO4 and NaCl in cast iron pans, hence the Fe
contamination that’s still so common in ‘hardware store muriatic acid’. |
Most hardware store muriatic acid is a byproduct of the steel industry. It's also made via the chlorination of hydrocarbons. Honestly, the stuff is
an industrial waste product, and they should be paying you to take it.
CaSO4 is a bitch to clean up afterwards. NaHSO4 on the other hand dissolves away. Using CaCl2 is more economical per unit of H2SO4, but NaHSO4 is
easier all around.
[Edited on 2/5/11 by Melgar]
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blogfast25
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John:
Where did you get those neat little taps anyway? They could be VERY useful elsewhere!
Why not try a good old fashioned Hoffman clamp to control the acid flow? Or a glass tap from an old burette or cracked separating funnel? Most of us
have these laying around...
I don't see the point to the second tap: potentially dangerous even: close it with acid in the generator and you've got pressure building up!
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peach
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Someone else has asked about the taps as well, for an entirely different purpose to what they're being put to here.
They're Hozelocks, the micro-irrigation things you find at B&Q in the garden section. They're £4 or so for two. But they are very nice when
they're not full of acid, they open and close very smoothly and, even in the example above, they provided a positive on and off, and fine control in
between. You can find them cheaper on eBay, no name brands, where they're about £1.50 but, by the time you pay the pound or more of postage, it's the
same price and you may as well get the Hozelocks at B&Q. Unless you're doing the entire garden as well.
You may also run into Gardena brand micro taps in the shops.
I have thought about using a Hoffmann clamp yes. I wanted to try the little taps because I thought they'd give better control, particularly if the
tubing is cold, which makes it quite a lot more rigid. As is clearly evident, even though they're designed to work on about 15psi for the garden
irrigation from memory, these rubber sealed taps are not suitable around strong acids; and not just a bit, but entirely.
I also thought about using glass taps, but thought I'd try the plastic ones first as they're cheaper and easier to come by and, provided they don't
melt, not so brittle.
I have seen plastic taps that don't use washers, as you'd find them on lab glass, but finding them is a bit more effort - which is why I haven't tried
it again yet (I'll need to find some). If all else fails, I will use glass ones yes.
The second tap is there because I needed to make the connection to the top bottle (to equalise the pressure) through the cap, as melting the plastic
of the walls and bases doesn't work very well at all - it's too flexible. Because of that, the equalising tube has to be dunked into the acid as the
cap gets screwed back on. I was worried that a decent amount of acid would then run straight into the lower bottle (through the equalising tube) as I
turned the top one upside down. That extra tap there prevents that.
What is likely to happen if you forget to open it is that pressure will build up in the bottom bottle, and then stop any more acid coming down.
Provided the bottom bottle is open to the experiment, pressure shouldn't build up in the top bottle; a vacuum will, which will also prevent more acid
coming down. But you are right, you'd be best making sure it was open before starting.
The WORST thing to do would be to put a tap on the exit of the generator. That would allow the acid to come down to the salt, and it'd sealed, so
pressure would most certainly build up; in both bottles.
Here are two things I thought might also interest you;
Chemglass, and others, make addition funnels with a tap on the equalising arm for isolating the sample from the atmosphere in the glass at
specific points in the work. You imagine the fun that involves if you forget to open or close one at the right time!
QuickFit, and others, make these variants on the Hoffman clamps which feature a little roller on steps, so tubing can be proportionally
clamped off. I'm sure you can find these from RC model stores cheaper than QuickFit will sell you one for.
[Edited on 6-2-2011 by peach]
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blogfast25
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Definitely off the B&Q/eBay for some of these Hozelocks. The Aquarium People do some neat little (very proportional) air valves (needle, I
believe) w/o washer too. For use with silicone or PVC tubing. Not sure about RC shops: tend also to be expensive!
Nice bit of ‘plastic welding: almost all plastics are immiscible, the only popular case of miscible polymers is NBR/PVC. Even PE/PP is two phase,
even PP/EPR and LDPE/EPR…
Still not entirely convinced the tap in the equalising tube is really necessary.
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soma
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Came across this after doing a search on google. If anyone has access to the Journal of Chemical Education (A Convenient Way to Generate Hydrogen
Chloride in the Freshman Lab, Francisco J. Arnáiz, Journal of Chemical Education, 1995, 72 (16), 1139.) I'd appreciate a copy of the article.
http://curlyarrow.blogspot.com/2009/03/how-to-make-dry-hcl-g...
How to make dry HCl gas
[...] The standard approach that I’m guessing most chemists still use is to add conc. sulfuric acid to sodium chloride or conc. HCl. However,
avoiding the use of conc. sulfuric is desirable because it’s nasty and you’ll have to clean up afterwards. So in the interest of safety I would
recommend the addition of conc. HCl to calcium chlorid. It’s cheap, the HCl gas that you generate is completely dry, it’s relatively easy to clean
things up and the reaction is very easy to control. Here’s the original reference:A Convenient Way to Generate Hydrogen Chloride in the Freshman
Lab, Francisco J. Arnáiz, Journal of Chemical Education, 1995, 72 (16), 1139.
On the photo you can see one of my recent set-ups. Here I am adding conc. HCl to calcium chloride with a pressure equalising addition funnel and
bubbling the HCl directly into my reaction flask. Please note the use of a Pasteur pipette for bubbling the gas into the reaction flask. Do not get
tempted to use a metal needle. Also I often add a wash bottle between the reaction flask and the gas source in case of unexpected suck backs. D!
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Poppy
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Does the bubbles still disappear before leaving the catcher water when it is already nearing 37%?
HCl might be useful for:
precipitation of the common ion> for example bubbling through FeCl3 until it precipitates out as a solid
replenishing dissolving baths.
Halp
This way you can accomplish usefulness of the compost other that trying to creat a 90% solution out of it
[Edited on 3-26-2012 by Poppy]
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elementcollector1
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Another method (cannot remember source, think it's on YouTube) is to take the impure stuff from the hardware store, and place it in a sort of
dessicator-box setup, with distilled water in another beaker. Then you'll have a pure solution of half the concentration of HCl.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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annaandherdad
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I remember the source
| Quote: Originally posted by elementcollector1 | | Another method (cannot remember source, think it's on YouTube) is to take the impure stuff from the hardware store, and place it in a sort of
dessicator-box setup, with distilled water in another beaker. Then you'll have a pure solution of half the concentration of HCl.
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It's Robert Bruce Thompson, Home Scientist. You can find it under Youtube's search. As I recall he waited a month for the HCl to equilibrate between
the cheap stuff and the distilled water. And of course the final product will be less concentrated than the original.
Any other SF Bay chemists?
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AJKOER
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For those experimenting with Oxalic acid (H2C2O4) a more expensive route is reacting aqueous CaCl2 and H2C2O4:
CaCl2 + H2C2O4 --> 2 HCl + CaC2O4 (s)
where the Calcium oxalate is just about completely insoluble.
Oxalic acid is also sold in hydrated form, H2C2O4.2H2O, a white crystalline solid. Upon heating with dry CaCl2 and condensing the vapors should yield
pure concentrated HCl. EDIT: Or, given the reported (per Oxalic acid MSDS) reaction of H2C2O4 with strong oxidizers, even heating the dry hydrated
form of Oxalic acid may produce an accelerated decomposition (or explosive) reaction given the nature of anhydrous CaCl2 reaction with water.
Employing CaCl2.xH2O, or avoiding the reaction all together and proceeding with an aqueous synthesis, is advised.
MSDS Sources:
http://www.soest.hawaii.edu/krubin/MSDS/oxalicacid.html
"Incompatibilities with Other Materials: Reacts with furfuryl alcohol, silver, sodium chloride, and sodium hypochlorite. Contact with oxidizing
materials may result in an explosive reaction."
Also:
http://www.nilechemicals.com/OxalicAcid%20msds.htm
"Explosion: Reacts explosively with strong oxidizing materials and some silver compounds."
Also:
http://www.labchem.net/msds/75425.pdf
"Forms explosive salts with silver compounds, reacts explosively with chlorites, hypochlorites."
Also:
http://msds.orica.com/pdf/shess-en-cds-010-000030127001.pdf
"Hazardous reactions: Reacts exothermically with alkalis. Accelerated decomposition occurs when mixed with strong oxidising agents."
"Chemical stability:Vigorous reaction may occur with alkalies yielding heat and pressure, and with acid chlorides producing toxic fumes. May react
violently with alkali metals producing flammable hydrogen gas. Reacts strongly with oxidising agents, especially sodium chlorite and sodium
hypochlorite. Can react with some silver compounds to form explosive silver oxalates."
[Edited on 29-3-2012 by AJKOER]
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