# Density range of table salt?

Does anyone have a reference for the density range of common table salt $$(\ce{NaCl})?$$

A pure $$\ce{NaCl}$$ crystal has a density of $$\pu{2.16 g/cm^3}.$$ However, the salt granules in table salt don't pack perfectly — there's a lot of air mixed in.

I carefully measured some Morton's iodized table salt at home $$(> 99\%$$ $$\ce{NaCl};$$ remainder is calcium silicate, dextrose, and $$\ce{KI}),$$ and got a density of $$\pu{1.40 g/cm^3}*,$$ which gives a packing fraction of $$1.40/2.16 × 100\% = 64.8\%.$$

Interestingly, this is (within my measurement error) essentially the same as the $$64\%$$ random close packing limit for monodisperse frictionless hard spheres.

But I don't know how much variation there is in the density of table salt, and have been unable to find a reference online.

*Here is how I measured the density: I started with a metal 1 tbsp measuring spoon. I didn't trust that its volume was actually 1 tbsp, so I filled it with water and measured the weight of the water (14.25 g) with a calibrated centigram scale, and its temperature (76 F) with a thermometer. Since water @ 76 F has a density of $$\pu{0.997189 g/cm^3}$$, the volume of the measuring spoon was:

$$V_{spoon} = \frac{\pu{14.25 g}}{\pu{0.997189 g/cm^3}} = \pu{14.2902 cm^3},$$ as compared with the actual volume of a tablespoon, which is $$\pu{14.7686 cm^3.}$$

I then weighed a level tablespoon of salt (20.00 g) and, from this, determined that

$$\rho_{table salt} = \frac{\pu{20.00 g}}{\pu{14.2902 cm^3}}= \frac{\pu{1.40 g}}{\pu{cm^3}}$$

• Aside of references, I suggest experiments with different table salt sources of different grains. And/or, for a given source of rough grains, try crunching it in grinding mortar, how it affects its density. Sure, the way of grinding and shapes of grains would have their affect too. – Poutnik Aug 26 at 6:18
• I see, such idea has come to my mind too, but too late. Random_close_pack - For_spheres > Poured random packing Spheres poured into bed 0.609 to 0.625 Close random packing E.g., the bed vibrated 0.625 to 0.641. OTOH, I see no reason to expect equal spheres or spheres at all. – Poutnik Aug 26 at 6:37
• There is really no way to exactly determine the packing fraction theoretically. It obviously depends on the distribution of the particle sizes, and the shapes of the particles. – MaxW Aug 26 at 8:23
• @J... "There is no point for anyone to study this or measure it for salt, specifically...It's also pointless because....." Nonsense. What you wrote is demonstrably false. This was a practical question about the distribution of density for commercially produced table salt, which is in turn determined by the variation in the manufacturing process. Such information is important to individual table salt producers, so that they know the variation in salt volume as they fill each container by weight (or alternately, if they sell by weight, but fill by volume.... (continued)... – theorist Aug 26 at 20:21
• .... it tells them what needs to be the minimum volume to ensure the weight is achieved. It's also of practical importance for those who use table salt in large quantites (e.g., food processors), and whose formulations are by wt., but find it more convenient to measure by vol. instead. Knowing the variation in density tells them whether density variation would be a significant source of error. You claim this ques. is "pointless" b/c "everyone will have salt made in a different way", but you're not thinking it through – the point of the ques. is precisely to know what this mfr. variation is. – theorist Aug 26 at 20:37

The density of $$\pu{2.17 g/cm³}$$ refers to the bulk density, i.e. within a crystal of NaCl. In chemical engineering, the terms of powder density, tapped powder density and settled apparent density take into account for the air between the grains of a solid. Especially the later recognizes that there may be a difference between the solid simply poured into a container, and after light compression (still with air gaps between the grains) after applying a little pressure e.g. if you shake and knock the tin filling with freshly ground coffee powder.
References like this, this, this, or this .pdf state powder densities of $$\pu{1.378 g/cm³}$$ (fine table salt), $$\pu{1.282 g/cm^3}$$ (granulated salt, again from here), and $$\pu{1.089 g/cm^3}$$ (rock salt). From these values, your estimate of $$\pu{1.40 g/cm^3}$$ seems plausible.