With respect to the original investigator in the 2006 linked blog post, isn’t it rather obvious that a way to measure the total-dissolved-solids value, where th

With respect to the original investigator in the 2006 linked blog post, isn’t it rather obvious that a way to measure the total-dissolved-solids value, where those solids affect the way light refracts in water, is to use a refractometer? I would guess that different solids cause different amounts of refraction. Most beekeepers have a telescope refractometer that’s calibrated for checking water content in honey. (Wet honey bad, dry honey good.) You’d probably be able to use it for salt content too, for example, but if you brew coffee then put honey and salt in it, one measure of refraction obviously isn’t going to help you pick apart how much of each substance you have. (The original refraction post talks about this — sugar in your coffee will taint your refraction reading’s ability to proxy for TDS because now it’s measuring coffee+sugar. Although you could of course weigh how much sugar you put in the coffee. A handy technique if you have a cheap refractometer calibrated to a specific range into which the additional sugar can place you, and the deviation from which you can use to measure how strong your coffee is.)