There are generalized results of thermo-X-ray investigations of binary compositions of paraffins (C$_{n}$H$_{2n+2}$): 1) odd orthorhombic systems C$_{17}$-C$_{19}$, C$_{19}$-C$_{21}$, C$_{21}$-C$_{23}$, C$_{19}$-C$_{23}$; 2) even triclinic systems C$_{20}$-C$_{22}$, C$_{22}$-C$_{24}$, C$_{20}$-C$_{24}$; and 3) mixed odd-even systems C$_{20}$-C$_{21}$, C$_{21}$-C$_{22}$, C$_{22}$-C$_{23}$, C$_{23}$-C$_{24}$, C$_{19}$-C$_{22}$, C$_{20}$-C$_{23}$, C$_{21}$-C$_{24}$, C$_{19}$-C$_{24}$. Syntheses and investigations of 10-15 compositions for the each system displayed that a paraffin formation is a multifactor process.
For the first time a possibility of a rotary-crystal state as the characteristic factor of isomorphism for paraffins is taken into account, side by side with such well-known factors of a paraffin isomorphism as an even-odd specificity of a number n of mixed pure components and a difference of lengths of their molecular chains ($\delta$n).
Two types of the rotary-crystal state of paraffin homolog with 17$\leq n \leq$ 24 and of their solid solutions are divided: the low-temperature orthorhombic (Or$_{rot.1}$) and high-temperature hexagonal (H$_{rot.2}$) ones. They correspond to the types of a heat motion of molecules: chaotic-gyratory oscillations and a rotation. Odd and even paraffins turn into the low-temperature rotary-crystal state from the orthorhombic crystal phase (Or$_{cryst.}$) and triclinic crystal phase (T$_{c}$) respectively.
The unique phenomenon of a solid solution disintegration at a heating is interpreted through a use of this concept. A homogeneous solid solution disintegration to a crystal phase (a relatively long-chain one) and a rotary-crystal phase (a relatively short-chain one) was displayed in a narrow temperature range for all investigated systems to a some degree. It is connected with energetic state varieties of different length molecules forming a solid solution, i.e. with varieties of their rotary-oscillation motion.
The results of a paraffin isomorphism investigation at the room conditions are interpreted in a new way. Experiments display that a solid solution is orthorhombic if it contains a considerable amount of doped molecules, independently on mixing components: orthorhombic with orthorhombic, triclinic with triclinic or orthorhombic with triclinic ones. A binary phase field is displayed close to triclinic components for even and odd-even systems due to extremely limited isomorphism in triclinic phases (not more than 8 \%). It is possible to divide three types of binary phase fields: Or$_{cryst.}$+T$_{c}$, Or$_{cryst.}$+Or$_{rot.1}$ and Or$_{rot.1}$+T$_{c}$ it is the consequence of the possibility of two states of orthorhombic solid solutions already at the room temperatures: crystal and rotary-crystal ones. By the way, the change of the phase state of orthorhombic solid solutions in the direction from a long-chain component of a mixture to a short-chain one is characterized by the scheme: Or$_{cryst.} ->$ Or$_{cryst.}$ +Or$_{rot.1} ->$ Or$_{rot.1}$.
An isomorphic mixing ability is displayed in all systems at the difference of mixed molecule length delta n >= 4 not only at the series edges but at their midsts. The expressed polar character of the binary phase field boundaries is also connected with an energetic state difference of molecular components of a paraffin composition.
Thus, a phase state of mixtures of a concrete binary paraffin system can be achieved by variations not only of a temperature but of a composition too. One can synthesize already at the room temperature a rotary-crystal phase characterized by a series of specific properties, for instance by a high plasticity. There is absent such a binary paraffin system what displays a complete isomorphic mixture ability in the whole range of their compositions and temperatures of an existence.