= Solution
\b[Examples heavier than <water> are <Mercury>, <glycerol> and concentrated <sulfuric acid>; examples lighter than <water> are <ethanol> and <diethyl ether>.] “Heavier” here means greater <mass> for the same <volume>, rather than greater total <mass> in arbitrarily sized samples.
Representative room-<temperature> <relative densities>, with <water> as unity, are
|| <Liquid>
|| Approximate <relative density>
| <Mercury>
| 13.5
| Concentrated <sulfuric acid>
| 1.84
| <Glycerol>
| 1.26
| <Water>
| 1.00
| <Ethanol>
| 0.79
| <Diethyl ether>
| 0.71
These are illustrative values, not exact constants independent of <temperature> or composition. Dilution changes the <density> of <sulfuric acid>, <glycerol> and <ethanol> solutions.<NIOSH Pocket Guide to Chemical Hazards>[Glycerin, Sulfuric acid, Ethyl alcohol and Ethyl ether entries, Specific Gravity fields]{ref}<Mercury agent properties by NIOSH>[Agent Properties, <liquid> density at 25 °C]{ref}
A distinction from simply observing a floating layer is essential: <ethanol> is miscible with <water>, so it mixes rather than remaining as a permanent upper layer. <Diethyl ether> has limited <water> solubility and can form an upper layer. More broadly, <gases> are also <fluids>, but the natural comparison intended here is between <liquids>; <air> at ordinary conditions is much less dense than <liquid> <water>.
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