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I would like to increase the density of a given oil (or anything that repels water) so that it is slightly heavier than water; to be able to precisely control how slow the oil would fall in the water.

What can I add to the oil (or the water) to accurately set its density?

I am looking for a cheap solution, that I can easily do at home.

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    $\begingroup$ Something similar to lava lamps? $\endgroup$ – andselisk Mar 9 at 23:05
  • $\begingroup$ How are you planning on using these dense hydrophobic liquids? $\endgroup$ – Nicolau Saker Neto Mar 9 at 23:15
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    $\begingroup$ @andselisk yes, my goal is to make something like lava lamps ;-) $\endgroup$ – arthur.sw Mar 10 at 11:42
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    $\begingroup$ how about bromonated vegtable oil? $\endgroup$ – A.K. Mar 10 at 17:18
  • $\begingroup$ Bromonated vegtable oil seems nice; how can I make it? Where can I buy this? Should I mix brome and vegetable oil until I get the right density? $\endgroup$ – arthur.sw Mar 20 at 9:03
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Halogen-substituted aliphatic hydrocarbons are usually miscible with oils. Pick the compound by its density, price, safety, boiling point and other characteristics.

For example, trichloroethylene (trico) has a density of ~1.6 g/cm3, and a Material Safety Data Sheet shows a vapor pressure of ~60mm Hg at room temperature and a time weighted average (TWA) toxicity limit of 50 ppm (269 mg/m3) from ACGIH and OSHA. Though it's readily available, trico might be too toxic and volatile for your use. A similar chemical is tetrachloroethylene, sold as "perc", with the same toxicity issue.

In general, going down the halogen group increases density, so bromine or iodine substituted compounds would be denser than those with fluorine or chlorine.

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    $\begingroup$ I was going to suggest using mothballs (apparently 1,4-dichlorobenzene nowadays). Halocarbons are simple solutions, but toxicity is indeed an issue. $\endgroup$ – Nicolau Saker Neto Mar 10 at 10:12
  • $\begingroup$ Thanks for your answer! Sorry I am not active on this thread right now (but I am still interested! ). I am not a chemist at all, so I don't know where to buy "Halogen-substituted aliphatic hydrocarbons", nor which one to buy. I am looking for something safe, relatively cheap, and easy to manipulate. Once I get this, I just have to mix it with oil until I obtain the proper density? $\endgroup$ – arthur.sw Mar 20 at 9:08
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    $\begingroup$ @arthur.sw, see the example above: "trico" is commonly sold for removing grease spots, as is "perchloroethylene" AKA "perc". As for your use, assuming you want to make "lava lamps", yes, it would take a bit of experimenting, mixing light oil and denser additive to get something that just floats or sinks in water with a small temperature change. You would also need to experiment with dyes to see which ones will not mix into both liquids. $\endgroup$ – DrMoishe Pippik Mar 20 at 20:34

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