dessicant colour crystals

I have a tiny amount of blue-coloured dessicant crystals that I use to
dry telescope optics after cleaning. Does anyone know of a source of
these crystals? They turn pink when exhausted and can be heated to
re-generate them.

Lawrence Harris

"Lawrence" lawrence@astronomer wrote in message
s.com...
I have a tiny amount of blue-coloured dessicant crystals that I use to
dry telescope optics after cleaning. Does anyone know of a source of
these crystals? They turn pink when exhausted and can be heated to
re-generate them.

Been a long time since I did chemistry but I think what you are looking for
is Cobalt Chloride. Philip Harris www.philipharris.co.uk supply chemicals
to schools but I don't know if they supply to individuals. Failing that
approach the chemistry teacher at your local school (or get a parent to do
it for you) and see if they would give you some or order some for you.

Stan

"Lawrence" lawrence@astronomer wrote in message
s.com...
I have a tiny amount of blue-coloured dessicant crystals that I use to
dry telescope optics after cleaning. Does anyone know of a source of
these crystals? They turn pink when exhausted and can be heated to
re-generate them.
You have indicating silica gel. The indicating chemical is cobalt chloride
which is now considered to be toxic and is being replaced with other
indicators.

An indicating silica gel with none toxic indicator can be obtained from
GeeJay Chemicals Ltd. If you can't find a website then they are on 01767
682774. They are wholesale but will sell you small quantities at a
reasonable price. I think my 500 gram container of silica gel beads cost
around ten pounds. Instead of pink/blue the replacement indicator is
brown/green.

Hope this helps.

Sally

Many thanks Sally.

Lawrence


On Thu, 4 Dec 2003 15:00:11 -0000, "Sally"
wrote:


"Lawrence" lawrence@astronomer wrote in message
ws.com...
I have a tiny amount of blue-coloured dessicant crystals that I use to
dry telescope optics after cleaning. Does anyone know of a source of
these crystals? They turn pink when exhausted and can be heated to
re-generate them.
You have indicating silica gel. The indicating chemical is cobalt chloride
which is now considered to be toxic and is being replaced with other
indicators.

An indicating silica gel with none toxic indicator can be obtained from
GeeJay Chemicals Ltd. If you can't find a website then they are on 01767
682774. They are wholesale but will sell you small quantities at a
reasonable price. I think my 500 gram container of silica gel beads cost
around ten pounds. Instead of pink/blue the replacement indicator is
brown/green.

Hope this helps.

Sally

In message m,
Lawrence writes
I have a tiny amount of blue-coloured dessicant crystals that I use to
dry telescope optics after cleaning. Does anyone know of a source of
these crystals? They turn pink when exhausted and can be heated to
re-generate them.

Silica gel loaded with a cobalt chloride salt as indicator. Pink when
wet pretty blue when dry (and basis for a simple invisible ink).

There was a minor panic last year sometime about the cobalt salt being a
potential carcinogen. I don't recall what happened in the end. I think
it is still widely used in most chemical labs but the loose stuff is a
menace with optics.

Photographic shops sell them for keeping lenses moisture free.
(Ideally you want them in a sachet so silica dust can't escape)

Regards,
--
Martin Brown

Hello Martin

Sally sent me just the info needed (couple of messages back) and I shall
order a tub in the morning.

best wishes

Lawrence

On Thu, 4 Dec 2003 18:16:30 +0000, Martin Brown
wrote:

In message m,
Lawrence writes
I have a tiny amount of blue-coloured dessicant crystals that I use to
dry telescope optics after cleaning. Does anyone know of a source of
these crystals? They turn pink when exhausted and can be heated to
re-generate them.

Silica gel loaded with a cobalt chloride salt as indicator. Pink when
wet pretty blue when dry (and basis for a simple invisible ink).

There was a minor panic last year sometime about the cobalt salt being a
potential carcinogen. I don't recall what happened in the end. I think
it is still widely used in most chemical labs but the loose stuff is a
menace with optics.

Photographic shops sell them for keeping lenses moisture free.
(Ideally you want them in a sachet so silica dust can't escape)

Regards,

Martin Brown wrote:
There was a minor panic last year sometime about the cobalt salt being
a potential carcinogen.

Really? I had a test tube of the stuff in my first ever chemistry set
when I was about 8 years old.

Best,
Stephen

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In message , Stephen Tonkin
writes
Martin Brown wrote:
There was a minor panic last year sometime about the cobalt salt being
a potential carcinogen.

Really? I had a test tube of the stuff in my first ever chemistry set
when I was about 8 years old.

So did most of us in that era. Ditto for the asbestos heat proof tile.
And the Platinum pen secret agent invisible ink was cobalt chloride
solution too.

It was last year sometime that the proverbial hit the fan. Probably a
vast overreaction to what sounds like a very tiny risk. Web search
should get it.

In the Belgian chemical industry smokers theoretically have to file a
hazardous experiment notice before going outside the front door to smoke
tobacco (experiment involving atmospheric release of known carcinogens).

Regards,
--
Martin Brown

Stephen Tonkin wrote:

Martin Brown wrote:
There was a minor panic last year sometime about the cobalt salt being
a potential carcinogen.

Really? I had a test tube of the stuff in my first ever chemistry set
when I was about 8 years old.

Best,
Stephen

One of its effects only emerges decades later - the sufferer may
unaccountably fall asleep just before important events...

-----------------------------
Martin Frey
http://www.hadastro.org.uk
N 51 01 52.2 E 0 47 21.1
-----------------------------

On Thu, 04 Dec 2003 23:46:53 +0000, Martin Frey
wrote:

Stephen Tonkin wrote:

Martin Brown wrote:
There was a minor panic last year sometime about the cobalt salt being
a potential carcinogen.

Really? I had a test tube of the stuff in my first ever chemistry set
when I was about 8 years old.

Best,
Stephen

One of its effects only emerges decades later - the sufferer may
unaccountably fall asleep just before important events...

You just wouldn't let it lie would you!

--
Pete
Homepage at http://www.pbl33.co.uk
CCD/digicam astronomy