Thermodynamics of Leather Dyeing

The interaction of a specially purified hide powder, the preparation of which is described, and a series of pure dye acids has been investigated by determining the distribution of the colouring matters at equilibrium, usually at ten points on the titration curve. Reciprocal plots gave a mean saturation value of 1·00 milliequiv/g collagen. The following affinities (kcal/mole) were obtained at 25°C: C.I. Acid Orange 7–10·6 ± 0·3, C.I. Acid Orange 8 ‐11·0 ±0·3, C.I. Acid Red 88 –11·7 ±0·2, C.I. Acid Red 13 –16·5 ±0·6, and C.I. Acid Red 27 –21·2 ± 0·6. At 45°C the affinity of the first dye acid was –10·9 ± 0·4 kcal/mole, leading to a heat of dyeing of – 6 kcal mole and an entropy of 15 cal/deg.