**3.2. Velues derived from amount and mass of substance**

When building a system of units derived from number of substances the first values should be the values that are expressed only through the basic units of the system. The diagram below illustrates this requirement.


This scheme shows that its logical completion needs entering another derived value. This may be the density of the amount of substance, which is proposed to be denoted by symbol σ.

The density of substance quantity σ is a physical value equal to ratio of the amount of a substance to its volume. The equation determining σ is as follows:

$$\sigma \mathbf{v} / \mathbf{V}.\tag{1}$$

According to this equation the dimension of σ is expressed by the ratio of L-3 N, where L and N are symbols of the dimension of length and amount of substance. Unit of measure for σ is "mol per cubic meter", which is in SI units equal to the density of the amount of substance, under condition: if the volume of amount of substance is one cubic meter, then the amount r of substances is one mol.
