You do have a good point there. I just did a regression on the silver data ( on line java applet for that is at http://intrepid.mcs.kent.edu/~blewis/stat/lsq.html ). The linear does not fit very well, and the quadratic fits pretty well, The cubic fits very well, but it has a minimum around 25, which we know is incorrect. So I think the quadratic is probably the best representative of the three..
The formulea is: y = 411.1764282955657 + 0.3112651021088278x + 0.005722307218039878x^2 This produces the table shown at http://silver-lightning.com/cgi-bin/silver.pl Now one thing becomes clear rather quickly. The absorption wavelength does not change rapidly with size as the size gets smaller. For instance, from 0 to 5 the wavelength changes by less than 2 nm, and from 95 to 100 the wavelength changes by almost 7nm. Thus the yellow range of particle sizes is extremely wide! But another thing to note is that true to form, this extrapolation is off, and significantly so as the particle size gets smaller. We KNOW that CS is clear when the size gets small enough, but the generated extrapolation shows it to still have a yellow color all the way to 0, absorbing in the violet range since it never goes below 380 nm ( http://www.sencore.com/custsup/color/Color_Analysis.htm ). Thus we still need at least one good data point in the area under 10 nm to get a good curve fit. Marshall The program generating the data is: ! /usr/bin/perl print "Content-type: text/html\n\n"; print "<table border=0 cellspacing=0 cellpadding=0><th>size nm</th><th>absorp. peak nm</th></tr>"; for ($x = 0; $x <100; $x += 5) { $y = 411.1764282955657 + 0.3112651021088278*$x + 0.005722307218039878*$x*$x; print "<tr><td>$x</td><td>$y</td></tr>"; } print "</table>"; Ivan Anderson wrote: > Yes, it would seem that gold coloured silver sols start at particle > sizes of about 60 - 75nm (0.060 - 0.075 micron), but the data given > does not tell us at what point the yellow colour first appears other > than <38nm (<0.038 micron). > > If I remember correctly this data seems to be at odds with the results > obtained by Frank Key? > > Ivan. > > > -----Original Message----- > > From: Marshall Dudley [mailto:[email protected]] > > Sent: Saturday, 31 August 2002 2:18 a.m. > > To: [email protected] > > Subject: Re: CS>Light-Scattering > > > > > > I have looked for years for the information in table 3! It > > seems all our > > estimates of particles size for yellow and gold sols has > > been on the low > > side by a factor of 2 to 4. The yellow particles are way > > over the size > > often given as the range of acceptable sizes which goes up to 15 nm. > > > > This article is definitely a keeper. > > > > Thanks for finding it. > > > > Marshall > > > > Ivan Anderson wrote: > > > > > An in depth investigation of light scattering, absorption and > > > transmission, in gold and silver sols. Has some colour > > photographs of > > > silver sols. > > > Warning: scientific and technical...just ignore the math, perhaps > > > start at page 13. > > > > > > http://www.geniconsciences.com/root/files/1293.pdf > > > > > > Ivan > > -- > The silver-list is a moderated forum for discussion of colloidal silver. > > Instructions for unsubscribing may be found at: http://silverlist.org > > To post, address your message to: [email protected] > > Silver-list archive: http://escribe.com/health/thesilverlist/index.html > > List maintainer: Mike Devour <[email protected]>
