# When a mixture of water, sand, and salt is filtered, what passes through the filter paper?

Well it's not the sand; the $\text{filtrate}$ passes thru the filter paper.
The sand is retained by the filter paper; here the sand is the $\text{filtrand}$. However, the $\text{filtrate}$, that which passes thru the filter paper is a solution of salt in water. Often, when we perform a filtration, we add a bit of Celite to the starting mixture, which traps insoluble materials, and allows the filtrate to pass thru the filter quickly.