Re: pentahydrate or anhydrous?

From: Richard Knoppow ^lt;>
Date: 11/21/05-10:55:26 AM Z
Message-id: <001001c5eebc$626a8ea0$48685142@VALUED20606295>

----- Original Message -----
From: "BOB KISS" <>
To: <>
Sent: Monday, November 21, 2005 5:19 AM
Subject: RE: pentahydrate or anhydrous?

> Good question!
> The photo lab index seems to suggest that most formulae
> which call for Hypo
> or Sodium thiosulfate but do not specify which flavor are
> referring to the
> this correct?
> Please check my website:

   Formulas from old books generally specify crystalline
hypo, i.e., pentahydrate. I think this is because the
anhydrous variety was simply not available. Anhydrous works
fine in these formulas providing the weight is adjusted. If
anydrous is used the amount is 64% of crystalline.
   One other difference is that crystaline hypo is very
endothermic so its mixed with very hot water. Anhydrous hypo
has little heat of solution so should be dissolved in room
temperature water.

Richard Knoppow
Los Angeles, CA, USA
Received on Mon Nov 21 10:58:38 2005

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