# When finding the density of a liquid, why must you first find the mass of a graduated cylinder alone?

Let's start with $\text{density}$. How do we define it?
$\text{Density, } \rho$ $=$ $\text{Mass"/"Volume}$.
Now clearly, when we make such a measurement, it is useful to measure a large mass, and a large volume simultaneously to make the measurement. So take a $100 \cdot m L$ graduated flask, measure the tare, i.e. the empty mass $\left(i\right)$, and then fill it to volume, and then take the mass $\left(i i\right)$ when full.
$\left(i i\right) - \left(i\right)$ is the mass of the liquid, and thus, $\rho = {\underbrace{\left(i i\right) - \left(i\right)}}_{\text{mass of liquid"/underbrace(100*mL)_"volume of liquid}}$ with units of $g \cdot m L$, or equivalently $g \cdot c {m}^{-} 3$. Is this what you want?