Abstract

An isothermal calorimeter of the Bunsen type, using diphenyl ether as the calorimetric liquid, has been designed and constructed. It has been used to measure the enthalpies and specific heats of acetone-dehydrated skin and various experimental leathers, as functions of temperature from 28 to 65°C. For the skin and four of the leather samples, the dependence of specific heat on moisture content over the range 0 to 25% has been studied. Enthalpy determinations have also been conducted for certain leather constituents and for three synthetic substitutes.

The temperature dependence of the specific heats of the leathers gave a coefficient of 33 x 10⁻³ per K. The coefficient for the synthetic substitutes was zero. From 7 to 25% moisture content, the relation (Cp)m = (Cp)o (1 + 0.039m) is valid to about ±2%. This corresponds to an apparent specific heat of water in the leather of 5.33 x 10⁵ joule/Kg·K (1.27 cal/g·K). Below 7% moisture, the specific heat remains almost constant down to 2% moisture, after which a further decrease is observed. The effect of fat content and the amount of retannage on specific heat shows reasonable agreement with the additivity of their specific heat contribution; however, low chrome additions seem to affect the specific heat by causing a structural modification.

An apparatus for measuring thermal conductivity, of the twin plate guard ring type, has also been constructed. The design allows rapid measurement of the weight, and thus the moisture content, of split samples. Some preliminary results are presented.