# What is a solute that would give a water solution whose density is greater than 1.6*g*cm^-3?

You want a water solution denser than $1.6 \cdot g \cdot c {m}^{- 3}$?
You've tried with salt, but sodium chloride is not particularly soluble in water. A saturated solution of salt in water has a density ($\rho$) of approx. $1.2 \cdot g \cdot m {L}^{-} 1$. This density does not change much with temperature. For reasons I am not going to go into, halite dissolution in water does not vary with temperature.
There might be other (and cheaper!) alternatives, but a polytungstate solution might fit your requirements. These solutions have very high densities (approx. 3*g*mL^-1). Zinc chloride solutions can also have very high densities, but you will have to dig for the details.