203 
the same reason as with the movements of the anti-tartaric acid. In 
the trans-cyclohexane diol the OH-groups always remain very far apart ; 
indeed, we have not been able to obtain an acetone-compound, nor 
has an influence been observed on the conductivity of the borie acid. 
Another confirmation was furnished by the cis- and transcyclo- 
heptane diols. 
When Sacusr’s calculations are applied to them, the OH-groups, 
both in the eis- and in the trans-diol, get in their movements into, 
or nearly into the same plane with and on the same side of the 
C-atoms, which they adjoin. Now acetone compounds have actually 
been obtained, and increase of the conductivity of boric acid has 
been observed, both in the cis- and in the trans-diol; accordingly 
our measurements are in perfect harmony with what is to be 
expected in the movements of this system as undulatory surface. 
According to this view there is, therefore, no tension in the six- 
and sevenring-systems, even less than in the five-ring, and in faet, 
we knew this already from the measurements of the heats of com- 
bustion of the cyclo-paraffins. The very accurate determinations by 
STOHMANN, Rorn, and ZuBow leave no room for doubt that the 
increase of the heat of combustion per CH,-group of C,H,,, C,H,,, 
C,H,, does not amount to more than has been found in the paraffins, 
which ought to have been the case with increasing tension. 
This result seems to be in conflict with the experiences obtained 
about the ring-closures. When there is no ring-tension present in the 
saturated rings with more than six atoms, why are not they formed 
as easily as the five-rings,and why are they also clearly less widely 
spread in nature? 
This more difficult formation is, indeed, strikingly illustrated by 
the very low constant of equilibrium of the system propane diol 
1.3 + acetone, especially when compared with the corresponding 
propane diol 1.2 + acetone, the difference of which rests on six- 
ring closure against five-ring closure (see above). 
An answer is easy to give also here. 
The probability that the two OH-groups in the propylene glycol 
1.2 assume a favourable position with regard to the acetone molecule 
is so much greater than for the 1.3 isomer. In the propane diol 1.2 
a rotation of the molecule parts round a single bond suffices, whereas 
in the propane diol 1.3 the paths of the OH-groups are much more 
involved and intricate, so that in the same space of time they will 
certainly assume a favourable position much less frequently. 
We may summarise the result of this study as follows: 
