How to dry NaCl?

luxikon · Nov 23, 2009

I guess my NaCl absorbed water because the bottom of the batch sticks to the paper after weighing. Is it possible to dry it in a microwave without damaging it? If yes, how long will it take to dry about 10 g?

Marco B · Nov 23, 2009

Well, to be honest, I am probably one of the last persons on this globe not having a microwave, but NaCl is just plain household salt. So although you can just as well buy a new bottle in your local supermarket, putting it in your microwave shouldn't hurt... Unless you've seen your microwave going up in smoke last night trying to heat your ready-made heavily salted supermarket lasagne!

luxikon · Nov 23, 2009

Marco,

I know that salt from the supermarket is not pure NaCl. It contains at least iodide if not other ingredients. So I can't use it for my self made Perceptol. The NaCl I bought was more expensive than just salt. So for me it's worth drying it.

By the way: I use the microvave only for photography/laboratory purposes.

Klaus

Nicholas Lindan · Nov 23, 2009

In the US, salt sold for pickling/canning is pure salt without any additives. It can be used successfully to make Microdol.

To dry: put the salt in a flat pan; put the pan in a warm oven for a few hours; pour immediately into a glass jar; and put on a tight lid.

Marco B · Nov 23, 2009

luxikon said:
Marco,

I know that salt from the supermarket is not pure NaCl. It contains at least iodide if not other ingredients. So I can't use it for my self made Perceptol. The NaCl I bought was more expensive than just salt. So for me it's worth drying it.

By the way: I use the microvave only for photography/laboratory purposes.

Klaus

Ok, I wasn't so much aware of NaCl being a key ingredient of some developers. But to be honest, I neither mix my own photographic chemicals, nor had a really good look at "ingredient lists" for doing that.

I am pretty sure that here in the Netherlands, you can buy both Iodide containing, and non-Iodide containing salt in the supermarkets, although the first are more common on the shelves. Anyway, is in terms of quantity, the impurities in salt really relevant (at least the industrially purified, non sea-salt versions)? I think even plain house hold salt is already very pure.

And if I look at my Iodide containing household salt, and do the calculation right, it contains about 150 microgram of Iodide per 6 grams of salt, that is less than 0.0025%!

Would that really matter :confused:

Marco

Anon Ymous · Nov 23, 2009

Marco B said:
...And if I look at my Iodide containing household salt, and do the calculation right, it contains about 150 microgram of Iodide per 6 grams of salt, that is less than 0.0025%!

Would that really matter :confused:

Marco

I was thinking about it lately and had a look at my table salt. It contains KI at 48ppm, E536 (Potassium Ferrocyanide) at 10ppm maximum and an unknown amount of Sodium Carbonate. Would it be really that bad?

BTW, how much did your pure NaCl cost Klaus?

luxikon · Nov 23, 2009

The problem is not the costs but how to get my NaCl dry again. Or is the quantity of water absorbed by the salt also neglectable? I need 6.66 g for the formula.

I've got my formula from another thread of this forum:
Here is Edgar Hyman’s Microdol Substitute Formula:

Metol....................................5 grams
Sodium Sulphite, anhydrous........100 grams
Sodium Chloride (iodine-free)... 30 grams
Water to make.......................1 litre of stock solution.

Robert Hall · Nov 23, 2009

Look for Kosher salt. It is pure salt. It will have the "U" in a circle on the package. (small print, like the copyright symbol, but a U)

mightyomega · Nov 23, 2009

Kosher salt with a capital K and kosher salt with a lowercase k are different things. Many table salts bear the circled U symbol, which indicates that the product is under rabbinical supervision for kosher-keeping people. Capital K Kosher salt is a coarsely ground salt used for preparing rabbinically supervised meat, and is the one that is iodide and additive free. Look for the package to say "Kosher Salt" prominently on the package. In the UK, it's sold as "Koshering salt".

luxikon · Nov 23, 2009

@ Nicholas

Does it go faster over a Bunsen burner?

Jordan · Nov 23, 2009

luxikon said:
I guess my NaCl absorbed water because the bottom of the batch sticks to the paper after weighing. Is it possible to dry it in a microwave without damaging it? If yes, how long will it take to dry about 10 g?

I strongly advise you not to try microwaving moist salt. Salt is a phenomenal absorber of microwaves and things will get out-of-control hot very quickly.

Dave Pritchard · Nov 23, 2009

Non-iodized salt is available in USA grocery stores. It is also available from aquarium supply stores. It is used to clean aquariums, and to supply salt for salt-water aquariums.

Photo Engineer · Nov 23, 2009

Jordan;

Although I agree with you, it turns out that several companies make "spiced" heat pads that are spices mixed with table salt in a muslin bag. These are intended to be heated in the microwave and then used on the neck, arm, wrist and etc. My wife has used one of these for several years. They seem to work just fine and don't overheat. I was kind of nervous about them, but they work.

I think that the difference might be related to moisture content. These things are very dry and remain dry.

Or, there may be a mixture of salt in the bag. Since it is not meant for human consumption, there is really no spec on these.

PE

Fanshaw · Nov 24, 2009

There is no problem drying sodium chloride in an ordinary oven. It is extremely stable to heat.

luxikon · Nov 25, 2009

Regarding purity Photo Engineer wrote in another thread:

Impurities in most all cases tend to inhibit the desired reactions.

Cases in point include halide salts where NaCl contains some Iodide, and therefore the photographic is changed. Varying Iodide content from batch to batch varies the effectiveness of NaCl.

Loris Medici · Nov 25, 2009

Here in Turkey you can buy both coarse kosher salt and refined iodine-free salt in the markets. Refined iodine-free salt will definitely contain some other ingredients such as sodium aluminosilicate or other anti-caking agents and even a substantial amnt. of potassium chloride if it's a low sodium product. Therefore if you're not absolutely sure, it's best to use pure sodium chloride - which is also very cheap here; something like USD 1.25 per kg! I'd try to microwave it for 5-10 minutes, depending on the amnt. in question.

Regards,
Loris.

Photo Engineer · Nov 25, 2009

Thinking about this, I find no reason for the salt to absorb so much moisture. Usually, Sodium Chloride sticks to itself and clumps, but does not go on to form a "slushy" material that sticks to other things than itself. My bottle is stored in a rather damp place (my DR), and has clumped but that is all. It still feels dry to the touch.

PE

Rick A · Nov 25, 2009

Seal your salt in a jar with a dessicant packet(silica) this will remove any moisture as well as keeping any more from entering.

Rick

lxdude · Nov 25, 2009

I think it would be preferable to to dry it in a regular oven because the moisture released will be vented away, unlike with any microwave oven I've owned.

Martin Aislabie · Nov 25, 2009

Why not use a conventional kitchen oven to dry your salt

Empty the remaining salt into something like a Pyrex dish, spread it out to maximise the surface area and put it in your oven

Set the oven temperature to something well above boiling point and leave for a few hours.

The hotter the oven then quicker the water will boil off

Pre-heating the oven will help reduce the water uptake as the salt sits in the open atmosphere

NaCl doesn't melt until aprox 800C and is an extremely stable compound - so it is almost impossible to damage it with domestic equipment

Allow it to cool in the oven (keep the oven door closed to help reduce (moist) air currents

A glass jam jar with a decent lid is a good a storage vessel

The process can be repeated indefinitely

Martin

How to dry NaCl?

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