Where a range is given, there are available several observations which differ. In most cases the differences are thought to be real, arising from differences in the rubber rather than from errors of observation. Where a single value is given, it is either because no other observations are available or because there seems to be no significant disagreement among values within the errors of observation. Where values are not given, data have not been found. Where dashes are shown, either the physical measurement is impossible or the constant in question is not adequately defined under the given conditions. 50 phr means “50 parts of carbon black by weight per 100 parts of rubber”, corresponding to a volume fraction of about 0.2. The values shown refer to specific vulcanizates cited in the corresponding references. Other vulcanizates may yield a broader range of values. The metric technical unit “kilogram force” or “kilopond” has been taken as 9.80665 newtons (980 665 dynes). Where an undefined calorie has been used by the respective authors, it has been taken as the thermochemical calorie equal to 4.1840 joules. Values are given for constants at a temperature of 25°C and a pressure of 1 normal atmosphere = 1.01325×105 Pa (where 1 Pa = 1 N/m2 = 10 dyn/cm2 = 10−6 bar).