Figure 71. A Mohr-Westphal density balance. This instrument was first described
in 1832 by the German chemist Carl Friedrich Mohr. It is a balance with two
arms, where the equilibrium is reached by adding weight on a tray. This type of
instrument was modified by G. Westphal who replaced the tray with an adjustable
counterweight. Julien Thoulet used this type of instrument in his studies.