Calculated for C₅H₁₀O₅. Found.
_M_ = 150 _M_ = 150.3
RAFFINOSE.
Calculated for
C₁₈H₃₂O₁₆.5H₂O. Found.
_M_ = 594 _M_ = 528
=149. Birotation.=—As is well known, dextrose exhibits in fresh
solutions the phenomenon of birotation. The authors supposed that
this phenomenon might have some relation to the size of the molecule.
They, therefore, determined the molecular volume of freshly dissolved
dextrose by the method of Raoult and found _M_ = 180. The high rotatory
power of recently dissolved dextrose is therefore not due to any
variation in the size of its molecule.
The mathematical theory of birotation is given by Müller as
follows.[121] In proportion as the unstable modification _A_ is
transformed into the stable modification _B_, the rotation will vary.
Let ρ = the specific rotatory power of _B_ and _a_ρ = that of _A_, both
in the anhydrous state. Let now _p_ grams of the substance be dissolved
in _V_ cubic centimeters of solvent and observed in a tube _l_
decimeters in length. The time from making the solution is represented
by θ. The angle of rotation α is read at the time θ. Let _x_ = the mass
of _A_, and _y_ = that of _B_, and the equation is derived.
_a_ρ_xl_ ρ_yl_
α = --------- + ------:
_V_ _V_