From: Bob Curtis <???????????>
Subject: P.D. request, submission

Steve:
I _think_ I recently sent you a request to add my name to your Pipes 
Mailgroup list - If not, please add me now.

I received the following forward from a reader of your group. He suggests 
I send you a re-print of several of my recent posts to asc for inclusion 
in response to a request on that mlist....

BTW, I've gotton a lot of good feedback on this series of posts - So far 
everyone who's responded is delighted with being able to callibrate their 
hygrometers. Feel free to edit/editorialize on this material - just don't 
change it's "technical" content!

>Date: Tue, 21 Mar 1995 12:54:31 -0500
>From: Marc Dashevsky <??????????????????>
>To: ???????????
>Subject: Pipes Digest Needs Your Help
>
>Bob,
>
>I think I recall you mentioning in a post that you don't get Steve 
>Masticola's
>Pipes Digest.  Anyway, the latest issue contains the following:
>
>| From: ????????????????
>| Subject: Prylene Glycol???
>|
>| Hi All,
>|
>|   I have heard alot of things about "Oasis" and Glycol to make a good
>| homemade humidors for cigars.  I have bought them both, and now don't know
>| how much of the glycol i should use with what amount of distilled 
>| water.. I
>| have heard 50-50. 20-80. but i don;t know.. If you could suggest 
>| something i | would appreciate it.. Thanks alot
>| David G.
>| (Please reply e-mail because i don't know how to get it otherwise)
>|
>| [ To whoever replies: I'd appreciate a copy for the next Digest, too!
>| -S. ]
>
>If you have the time, you might drop Steve a note at 
>????????????????????????
>containing your Propylene Glycol and Radio Shack hygrometer calibration
>posts to a.s.c.
>
>_Marc
------------------------------------------------------------------------
[submissions follow...]

Newsgroups: alt.smokers.cigars
Subject: Re: Buying propylene glycol
Date: 13 Mar 1995 19:06:52 -0500

Any solution with a fixed composition has a fixed vapor pressure at a
given temperature and total pressure.  If the solution has only one
volatile component (water), then the vapor pressure is caused by that
component only (i.e., you won't find PG in the vapor phase). By 
coincidence, the vapor pressure of a saturated solution of PG is about 
70%.

To put it more simply, PG is a hydroscopic substance - It absorbs moisture
from the enviroment (like a salt shaker does in humid weather). The
distilled water evaporates until the ambient humidity approaches 70%. At
that point the PG won't allow any more moisture in the air. This is called
"Vapor pressure". Conversly, if there is too much moisture in the air, the
PG solution absorbs the excess, bringing the system _down_ to 70% as well. 

PG is certainly not the only solution with a suitable vapor pressure for
cigar storage. As several posters have pointed out, a glycerine solution
will also work in a credo. Being a thicker substance, I feel that
glycerine solutions ultimately "plug-up" the pores of your medium,
reducing it's effective surface area. Both are non-toxic, but PG actually
has anti-bacterial properties, which means you may use it alone, where
glycerine should be mixed with some sort of inhibitor to prevent "nasties"
from growing inside your credo. (this is the "secret formula" in some 
glycerine based solutions).

--  
Newsgroups: alt.smokers.cigars
Subject: Re: Propylene glycol and distilled water?????
Date: 8 Mar 1995 23:07:34 -0500

> I have a few questions about this substance.. 
>I read a FAQ about humidors and this chemical came up alot.. Supposedly it
>is to be mixed with water and used to hydrate an "Oasis" foam.. Does the
>Propylene Glycon help make it so it will only humidify to 70%???

Yes, 71% specifically. PG is fairly hydroscopic. it will only allow water 
to evaporate till the ambient stabilizes at that level. It will also 
actually absorb moisture from a too-humid enviroment to stabilize at 71% 
as well. This makes it ideal for regulating a humidor.

>  I called the Pharmacy and it seems to be a big deal to get.. They said
>they would specially order it for me, and i have to sigh it out because it
>is not labeled for customers...  But they said they would get me a pint
>for 7.00.. is that good???

Hehehe. If you buy it mixed with water at a smoke shop, you'll pay 
upwards of $10/oz. Yes, I'd say $7/ pint is excellent! :-)

>How much distilled water do i mix with it??? 

50/50 to start.  It's not that critical, as the water evaporates
eventually anyway - the proportions are constantly changing because of
this. Don't forget to use distilled water to replentish is as needed. 

> Should i use the whole thing at once and hold onto the solution???  

It doesn't matter. Pre-mixed or not, it's a stable compound - It'll keep 
well for years. 

Good luck!

--  
Newsgroups: alt.smokers.cigars
Subject: Re: how oft. to add H2O to credo w. PG?
Date: 18 Mar 1995 15:25:22 -0500

??????????????? (ZARNOTT) writes:

>>I was fortunate enough to get a pint of propylene glycol from my local
>>pharmacy (after I explained what it was for) for $8.00.

>Why would you get the third degree about buying propylene glycol...do
>people use it in illegal drug production or something?

Pharmicologically (sp?), it's used as a solvent for oral and injectible 
drugs.... It also has many uses as a chemical solvent, as well as being 
used in many cosmetics.

And oh yea, it's also mixed with some pipe tobaccos and _cheap_ 
drug-store cigars so they won't require humidification (YUCK!!!).

--  
Newsgroups: alt.smokers.cigars
Subject: RS Hygrometer Calibration
Date: 19 Mar 1995 02:36:59 GMT

Well, here it is as promised - the long lost home callibration procedure
for the Radio Shack 63-855 Hygrometer, (also known as the "Airguide"
Hygrometer). Please read these instructions _very_ _carefully_ before
proceding - If you don't feel comfortable tinkering with sensitive
circutry, DON'T DO IT! 

Let's start with the safe part, checking it's callibration... Even if you
don't want to open it's case and adjust your hygrometer, you would be well
advised to check it's callibration. These are not the precision
instruments that some people think... The factory tolerance (given in it's
tech spec's) is plus or minus 5 points of humidity through the range
40-80%. That means your unit could read anywhere from 65 to 75% while in a
70% enviroment and _still_be_considered_in_spec!!! I've personally seen up
to an 8 percentage point difference between units before callibration. 

For a calibration source, we're going to use salt - NaCl - plain table
salt... Why salt? The following is a brief explanation of the chemistry,
originally posted to asc by Peter Shenkin of Columbia University. Don't
worry too much about the technical details - the point is that plain salt
will, when used properly will maintain an exact 75% humidity in a sealed
enviroment. 

>From Peter Shanken's original post:

"A saturated solution at constant temperature & pressure has a fixed
composition.  [[ Explanation in terms of the Gibbs Phase Rule omitted. ]]
Therefore, such a solution has a fixed vapor pressure. Thus, at constant
temperature, no matter how much solid NaCl and how much water are present,
the concentration of the NaCl in the water is fixed, just as long as both
the solution and the solid phase are present. Therefore such a solution
has a fixed vapor pressure. 

Now, it just happens to turn out that the vapor pressure of a saturated
solution of NaCl in H20 is about 75% of the vapor pressure of pure water
at any temperature close to room temperature.  This means that at
equililibrium, if there were nothing present except this solution and a
vapor phase in contact with it (no air), the pressure above the solution
would be about 15 mm_Hg, in round numbers, using 20 mm_Hg as the vapor
pressure of water near room temperature, again in round numbers.  As
mentioned earlier, the only gas providing the pressure abover the solution
would be water vapor."

OK, class dismissed - you've got it now, right? :-) Now to procedures.
You'll need a zip-lock baggie or other see-through container, about a
teaspoon of salt, and a small, shallow open container for that salt (a
shot-glass would be good) Gee, I love this high-tech lab gear.... ;-)

Place a teaspoon or so of salt in it's container and add a few drops of
water to get it wet. You don't want to disolve it, just get a good wet
pile of salt in your shot-glass. As the technical explanation above says,
you want the salt present in both a liquid _and_ solid phase - salt mush.
Place it in the baggie, along with your hygrometer. CAUTION - DON'T SPILL
ANY SALT ON YOUR INSTRUMENT! Be sure the Hygrometer isn't in it's "min" or
"max" mode, BTW. 

Seal the baggie with some air trapped inside (so it's not tight against
the hygrometer) and let it sit. Allow this to stabilize for _at_least_ 6
hours. (don't rush it!). After the internal "system" has stabilized, check
your reading WITHOUT OPENING THE BAGGIE. It should be _exactly_ 75%. If
not, note the deviation - this is how much your hygrometer is out.  Don't
be surprised if your reading up to 5 points out - unfortunately, that's
the factory tolerence of this instrument. 

Now that you know how far your instrument is out, you _might_ want to
adjust your hygrometer. CAUTION! Mess-up here, and you could ruin it!!!
There is no simple callibration knob to turn. To adjust this instrument,
you'll be re-adjusting the bias current of the sensor, then comparing it
to your callibration reference - the salt in the baggie. 

Remove the battery door, the batteries, and finally the back of the unit.
along the top edge of the PC board inside, you'll see two round, flattish
metal disks (micro-potentiometers). don't touch the left one, you'll be
working _only_ with the one on the right. First, look at it closely.
You'll see a tiny indent for a tiny screwdriver blade across the middle.
Sketch it's exact position carefully - this procedure might take several
days, and you _will_ forget the original orientation if you don't write it
down! 

You'll be turning this _right_ potentiometer (pot) a tiny amount to change
the humidity reading (1/8 turn might change your reading by 3 or 4%). Use
a very small screwdriver (like a jeweler's screwdriver), and don't change
it by much! If you were reading _above_ 75% in the callibration test, turn
this pot _clockwise_, again only a tiny amount... If your reading was low,
turn it slightly counter-clockwise... 

You can leave the back off to save some effort, and put the batteries back
in now. Be sure the "min" and "max" functions are turned off, and place
the hygrometer back in your baggie with the salt. Again, let it stabilize
for 6 hours, and DON'T LET IT TOUCH THE WET SALT! Check your reading, and
re-adjust if necessary. Be patient, you may have to try a few times to get
it right. If you feel you're getting nowhere, set the pot back to exactly
where it was when you started. 

When you're satisfied with your setting (set it to +- 1% of 75%) remove
the batteries, re-assenble the unit, and give it one final check. Once
you're done, light up one of your best cigars - you'll deserve it! 

OK, that's the clearest description I can write of this simple procedure!
I expect _somebody_ out there is going to screw it up and blame it on me,
so let me remind you now that you are doing this yourself - I won't take
any responsibility for your mistakes... Personally, I've re-callibrated 5
units now with this procedure. Even if you don't re-callibrate it, I'd
recomend that you test your hygrometers with the "salt standard". Just
knowing it's deviation might be enough for many readers. 

-------------------------------------------------------------------------

Whew! That's "the-best-of" my PG posts. Use whay you like, combine, 
editorialize, whatever.... And add me to your list!

--  
Bob Curtis <???????????> 
"smoke 'em if ya got 'em..."

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