**3.3. Amount of substance for some matters**

Method of measuring the amount of substance is count. Direct counting atoms and molecules does not seem reason-nable. Even the number of galaxies in the Universe is already not countable. For example, one of proposed models of the Universe considers it as an ideal gas, containing galaxies. Therefore, the amount of substance is calculated by measurement of volume or mass. Relations between the density of amount of substance σ with density ρ, specific volume v and molar Vmol volume of substance are revealed by joint solution of equations defining these values:

$$\mathbf{v} \circ \rho / \mathbf{M} = \mathbf{1} \;/\; \mathbf{v} \,\mathrm{M} = \mathbf{1} \;/\; \mathbf{V}\_{\mathrm{mol}}\tag{2}$$

Under calculating σ it is necessary to identify the structural element of the matter.
