What is used to soften water by the Clark's method?

Why does hard water not form lather with soap?

We use polymetaphosphates as water softeners as they:

What is 'plumbo solvency' referring to in the context of lead?

When temporary hard water containing $Mg(HCO_3)_2$ is boiled,the precipitate formed is of:

$A$ water sample contains $30 \, ppm \, MgSO_4$ and $19 \, ppm \, MgCl_2$. Calculate the hardness of water in $ppm$ in terms of $CaCO_3$ equivalent.