Of course - size and concentration both need to be considered. I should have thought of that. And I know how unreliable lasers can be with the several I've got. Thanks for your time anyway Marshall, appreciated. N.
Date: Thu, 12 May 2011 11:14:46 -0400 From: [email protected] To: [email protected] Subject: Re: CS>Tynall cone strength 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
