From: "\"Uncle Al\" Schwartz" <UncleAl0@ix.netcom.com>
Newsgroups: sci.chem
Subject: Re: School Child (and Father) need help
Date: Wed, 12 Feb 1997 15:13:45 -0800

Chuck Mugford wrote:

> My 13 year old daughter did an experiment measuring the time it took for
> different brands of non-coated asprin to start disolving in different
> temperatures of water. Now, of course, she wants to know what she was testing.
> 
> Could/would someone please direct us towards the type of reference materials
> we should be looking for? I assume the experiment had to do with with
> solubility(?) and the effects of temperature. Please keep in mind, this is
> only for an eighth grade science class.
> 
> Thanks in advance.

Talk to the FDA or the American Society for Testing Materials (ASTM). 
There are standard assays for tablet disintegration or dissolution
time.  http://www.search.com/

Getting a tablet to survive the world until ingestion and then rapidly
crumble is no small trick.  Once crumbled it can proceed to dissolve. 
Many formulations contain "cross-povidone."  This is a crosslinked
poly(vinyl pyrrolidinone) dust which would be very water soluble if its
molecules were not all welded together.  It is not hygroscopic, but it
swells like a champ in liquid water.

The tablet hits the juice, the polymer swells, everything crumbles, the
greatly enlarged surface area aids in rapid dissolution.

There are other strategies.

-- 
Alan "Uncle Al" Schwartz
UncleAl0@ix.netcom.com ("zero" before @)
http://www.ultra.net.au/~wisby/uncleal.htm
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