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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

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

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    $\begingroup$ 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. $\endgroup$
    – Poutnik
    Aug 26, 2020 at 6:18
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    $\begingroup$ 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. $\endgroup$
    – Poutnik
    Aug 26, 2020 at 6:37
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    $\begingroup$ 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. $\endgroup$
    – MaxW
    Aug 26, 2020 at 8:23
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    $\begingroup$ @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)... $\endgroup$
    – theorist
    Aug 26, 2020 at 20:21
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    $\begingroup$ .... 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. $\endgroup$
    – theorist
    Aug 26, 2020 at 20:37

2 Answers 2

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The density of $\pu{2.17 g/cm³}$ refers to the density 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.

However, these data lack to state the typical size of the grains (think about the diameter), as well as the dispersion of the grain sizes (presence of larger and smaller grains, equally known as particle-size distribution) of the samples characterized. Both influence the packing of the grains and thus the recorded density. In this perspective, the softer / more airy harvest of fleur de sel possibly packs much less dense.

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    $\begingroup$ Many commercial solid (powdery) products specify a density (usually not specified as to what kind!). If this solid is incorporated into a formulated liquid product which is a solution, or even a dispersion which eliminates air, the bulk density must be used to calculate the final product density. Then the actual product density is measured to provide a degree of quality assurance. Using the wrong density for ingredients causes no end of confusion. $\endgroup$
    – James Gaidis
    Aug 26, 2020 at 13:45
  • $\begingroup$ I don't wonder bodies like ASTM and ISO reference density measurements, not only practical ones (coal, or fertilizers for «commoners», but equally materials to deploy under pressure (e.g., coating) up to nuclear fuel ... $\endgroup$
    – Buttonwood
    Aug 26, 2020 at 14:19
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    $\begingroup$ "The density of 2.17 g/cm³ refers to the bulk density, i.e. within a crystal of NaCl" unfortunate sort of "typo", just delete "bulk" and it fixes the sentence. Please edit it, it confused me a lot. I'm not knowledgeable enough to 1% of you in this, but I'm positive most stuff online I find "bulk" actually means NOT within a crystal, that's what some people call en.wikipedia.org/wiki/Particle_density_(packed_density) (kind of the same as density, but it seems people that work with this use it), quoting the beginning of that article... (1/2) $\endgroup$
    – Santropedro
    Jun 11, 2022 at 12:38
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    $\begingroup$ "The particle density of a particulate solid or powder, is the density of the particles that make up the powder, in contrast to the bulk density, which measures the average density of a large volume of the powder in a specific medium (usually air).", here you can read the bulk density of salt at anval.net/Downloads/Bulk%20Density%20Chart.pdf ~1.3g/cm^3 (2/2) $\endgroup$
    – Santropedro
    Jun 11, 2022 at 12:38
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The density of table salt is 1200 mg/cm³ according to the USDA.

The USDA nutrition label for salt lists the density as 18 g/tbsp. That seems to be rounded to 0 decimals. However, the nutrition label also state that there are 6976 mg Na in 1 tbsp. Using that value and the atomic weights of Na and Cl, the calculated density is 17.77 g/tbsp, a more precise value. The density then is 1200 mg/cm³, rounded to 0 decimal places.

Doing the same calculations with the data for Morton table salt, 590 mg Na in .25 tsp, gives a density of 1218 mg/cm³. However, since 590 mg seems to be rounded to the nearest 10 mg, I think the USDA number is more precise.

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    $\begingroup$ As it reads, you have the density at 1.2 kg/cc. I think you might need to go in and do some editing - $\endgroup$
    – Todd Minehardt
    Sep 21, 2021 at 22:02
  • $\begingroup$ Double Argh. Proofed it again after correction. I think I got this time. Thanks @ToddMinehardt $\endgroup$
    – Wayne Goode
    Sep 21, 2021 at 23:59
  • $\begingroup$ @WayneGoode - Still no. I will edit it. $\endgroup$
    – Todd Minehardt
    Sep 22, 2021 at 0:01

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