Yes and no. Tyndall alone cannot tell you anything. That is because it
varies linearly with the concentration.
Tyndall varies to the 4th power of particle size (diameter)
Tyndall varies linearly with concentration, as does number of particles
with constant size
Concentration varies to the 3rd power of size given a certain number of
particles. (4/3piR^3 for a sphere)
Given those, we find the tyndall will vary linearly with particle size
if you maintain the same concentration (whereas it varies to the 4th
power if you maintain the same number of particles). This is because
if you double the particle size, you will get 16 times the tyndall off
of each particle, but you will only have 1/8 as many particles, thus
tyndall will also double.
That means that two solutions with the same tyndall, one 5 ppm, and one
20 ppm, will have sizes which are 4:1 different as well.
In addition the brightness of the laser can vary significantly from unit
to unit, and with battery life. A third problem, particles will not be
of a consistent size, but will have a range of sizes. The larger
particles will contain both more mass (% of the silver) by the 3rd power
of their size, and more tyndall by the 4th power. So larger particles
can increase the tyndall beyond what it would be if all particles were
the average size. And additional problem, especially if you add H2O2 is
that gas, often oxygen, will form on each particle, making it appear
larger and giving off a lot more tyndall. This in the extreme can cause
some CS (generally above 20 ppm) to almost appear milky when H2O2 is
added and have an extremely strong tyndall, although the actual
particles are really quite small (I believe typically 2 atoms each).
Marshall
On 5/11/2011 7:58 PM, Neville Munn wrote:
["Little TE means very small particles. Remember that the Tyndall varies
to the 4th power of the particle size, so if you halve the size, the
Tyndall goes down by 16:1."]
Marshall, or anyone else if they feel inclined, I'd like to run
something past you.
As ridiculous as this question may seem, I'd still like to hear what
you may have to say.
I've broken my Tyndall cone effect into five catagories...Nil, Faint,
faint/Good, Good, and Strong.
Not being the sharpest knife in the draw regarding mathematics, by
using your calculation as mentioned here, is it possible to get an
approximate {and I repeat, an *approximate* or Wild Arse Guess if you
like} particle size using the strength of laser beam through solution?
Eg; Faint may be 'x' particle size, Good may be 'y' particle size etc
etc, and praps all WAG's as I have indicated.
N.
