optical properties of coIloidal solutions of metals cannot be interpreted by reference only to the size of the particles. J. C. P. Relation between the Rotary Power of Optically Active Substances and their Chemical Constitution. D. CHARDIN and S. SIKORSKI (J. Rus3. Phys. Chem. Soc., 1907, 39, 703-731. Compare Guye, Abstr., 1800 1893, ii, 204, 561)-Guye'sexpression for the product of asymmetry contains about twenty-eight unknown quantities ; it was therefore simplified by assuming that all the

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... ntres of gravity of the side-groups lie on the axes of the asymmetric carbon atom, thus obtaining an expression, I, with four unknowns, namely, the distances of the C.G.'s of the side-groups from the asymmetric carbon atom. This was then further simplified by assuming these distances to be equal to 11. All t h e experimental work which has been performed so far to disprove Guye's theory really only leads to the rejection of formula 11. Accepting Guye's general theory and as:uming (1) that the distances of the C.G.'s from the asymmetric carbon atom are functions of the internal structure and distances from one another.of the atoms i n the side-groups ; (2) that the atoms rotate round the axes uniting t h e m ; (3) that, in general, the distances between the atoms depend only on their nature and not OD their position, it is deduced that the C.G. of any side-group describes a curve with its centre on the continuation of the corresponding axis of the asymmetric carbon atom ; since therefore the C.G.'s are constantly shifting their plane, the angle of rotation should alter periodically. This nlteration is not observed, either because the diEerence in the angles is too small or the time is too short, consequently the angle observed is the average, and the C.Q.'s to be considered in any formula should also be their average position, that is, they will coincide with the centres of the curves and will lie on the axes of the asymmetric carbon atom, Thorefore in active aliphatic compounds, formula I is applicable. Formulae are given for calculating the distances of the C.G.'s from the asymmetric carbon, and, by employing these in con junction with formula I, the distances of the elements from one another can be calculated ; thus the distance between two carbon atoms in the pentane derivatives containing one 01-two asymmetric carbon atoms is found to be 4-10. Again, for the derivatives of the amyl alcohol, CHMeEt*CH,R (where R = N , 0, S, C1, Br, &c.), the product of the atomic weight of the element R aud its distance from the carbon atom (termed 'I the atomic product," even if the weight considered is that of a group instead of a n atom) is a definite constant for each series in the periodic system, and equals one-half the sum or difference of the atomic product of the normal carbon chain with either one, two, three, &c., carbon atoms, and is positive for the even series, negative for the odd series. For example, glZ, (the atomic product of the carbon chain containing one carbon atom) = 61.5, g2Z2 = 139.4, g3Z8 = 222.7, then for the second series, that is, for the elements, nitrogen, oxygen, fluorine, the atomic product = 139.4. For the third series, chlorine, for example, = (61.5 + 139*4)/2 = 100.45. For the fifth series, bromine=(61*5 + 134.9 + 222*7>/2= -211.9. If the replacement of one element by another changes the sign of the angle of rotation, then half the ditference must be taken