----- Original Message ----- From: Marshall Dudley <[email protected]> To: <[email protected]> Sent: Tuesday, 28 September 1999 03:47 Subject: Re: CS>Fw: Cond. meter pt 1 was CS>Standardization - A Call for Standards!
> Ivan Anderson wrote: > > > > It seems to depend upon what the particles are composed. If the > > > particles contain a number of uncharged atoms along with charged > > atoms, > > > then the conductivity is the sum of the charges, but the concentration > > > of recoverable metal is the sum of both. (This is the most compelling > > > reason to limit the amount of cathode build up, as some inevitibly > > > enters the solution.) > > > However, if the particles are comprised wholey of charged atoms then > > the > > > conductivity reflects the recoverable metal. > > Actually the conductivty will be proportional to the sum of the charges TIMES > THE MOBILITY OF THE CHARGES. If we are talking about atoms, then this term > falls out, but in the case of a colloid, the larger the particle the lower the > mobility (visulize a one pound pull on a toy boat vs a full size boat to see > how size can change the mobility). That makes it really difficult > (impossible?) to determine ppm and or particle size from a conductivity > measurement alone. In fact the mobility of ions (or particles as I presume you mean) can actually increase with larger radii. The charge at the surface of a sphere decreases in proportion to the the increase of the radius squared. As ions and charged particles carry with them water molecules in what is called the hydration sphere which is dragged through the water with them. Small ions due to their higher surface charge carry a larger hydrodynamic radius with them than larger ions and move more slowly through the water. [Physical Chemistry - Atkins] How this actually relates to the particle sizes in colloidal silver is unclear, but if the results of my investigations (via ISE vs AAS measurements) are repeatable with a conductivity meter then that is very good news indeed. However, if they are not, then some work is required by me (or someone) to relate conductivity readings to ISE (or AAS) readings to produce graphs of concentration for different recipes. > Marshall Ivan -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: [email protected] List maintainer: Mike Devour <[email protected]>
