Isomerides, dynamic

Doubtj however, arose as to the validity of the above explanation, and this doubt was confirmed by the isolation of the two isomerides in the solid state, and also by the fact that the velocity of change of the one isomeride into the other could in some cases be quantitatively measured. These and other observations then led to the view, in harmony with the laws of chemical dynamics, that tautomeric substances in the dissolved or fused state represent a mixture of two isomeric forms, and that equilibrium is established not by m/m- but by in r-molecular change, as expressed by the equation... 

By reason of the importance of these phenomena in the study more especially of Organic Chemistry, a brief account of the equilibrium relations exhibited by systems composed of dynamic isomerides may be given here. ... 

It has already been indicated (p. 53), that in the case of sulphur we have a substance which can give rise to different molecular species which, in the liquid state, form an equilibrium mixture. For this reason, sulphur will behave not as a purely unary system, but in a manner similar to that of dynamic isomerides discussed in this chapter. We shall therefore discuss briefly the more important equilibrium relations of sulphur from this point of view. 

From what has just been said, therefore, we see that the equilibrium relations between crystalline sulphur and liquid sulphur will be similar to those found in the case of dynamic isomerides. As in the case of such substances, the crystalline forms of sulphur may exhibit various melting- or freezing-points, and only when there is complete absence of the molecular species S,r or do we obtain the ideal or true freezing-point that is, the equilibrium temperature between crystalline sulphur... 

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