Aqueous solubilities have been determined at 25° and 80°c. for a range of purified disperse dyes. The solubilising effect of a number of dispersing agents has been examined. It is shown that aqueouS solubility has some bearing on the rate of dyeing of disperse dyes and largely governs their levelling power. Addition of a dispersing agent to an acetate rayon dyebath reduces the percentage exhaustion to an extent which is proportional to the degree of solubilisation.

The behaviour on unmodified polypropylene fibre and film of two commercial disperse dyes and Dimethyl Yellow has been examined. The results indicate that disperse dyes capable of dyeing polypropylene fibre have high diffusion coefficients and low saturation values. Linear adsorption isotherms were obtained with Dimethyl Yellow. The behaviour of polypropylene fibre towards disperse dyes in general is discussed.

Equilibrium isotherms have been obtained at 80d̀c. with acetate rayon and five disperse dyes. Two azo dyes showed a linear relationship up to saturation between dye on the fibre and dye in the aqueous phase. Non‐linear curves were obtained with three anthraquinonoid dyes, but a straight line was obtained when a solubilisate of 1‐methylamino‐4‐anilinoanthraquinone was used in place of a dispersion. With purified Dispersol Fast Scarlet B the slope of the isotherm was found to be independent of liquor: yarn ratio, and inversely proportional to the concentration of dispersing agent over a limited range.The adsorption by acetate rayon of purified Lissapols C and LS has been studied at 80δc. Both detergents hydrolyse gradually in hot aqueous solution.

Although disperse dyeing appears at first sight to be very different from the application of dyes which are readily soluble in water, closer study shows that the two processes are in fact similar. But disperse dyes are not ionised, and dyeing does not depend on the presence of salt‐forming groups in the fibre molecule, so disperse dyeing systems are much easier to treat theoretically than the older systems. In spite of the absence of ionising sulpho groups in the dye molecule, disperse dyes are not completely insoluble in water. They diffuse into the fibre from a very dilute aqueous solution, which, as dye is removed from solution by the fibre, is replenished owing to the presence of fine particles of suspended dye. At equilibrium a linear relationship is found between dye on the fibre and dye in the bath, so the dyeing process resembles the partition of a solute between two immiscible solvents.

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The vapour pressures, latent heats of sublimation and associated entropy changes for two 1-aminoanthraquinone derivatives and two 4-nitro-4'-aminoazobenzene derivatives have been found by an effusion method. These compounds have a vapour pressure of 10-4-10-6 mm Hg over the temperature range 110-165°C. The heats of sublimation are discussed in terms of the molecular structure.

The aqueous solubility of a number of disperse dyes has been determined. Some have appreciable solubility at the usual dyeing temperature (SOo C). Even the most insoluble are solubilized to some extent by the dispersing agent normally added to the dyebath, and in these cases the rate of dyeing of cellulose acetate rayon is increased. The evidence now available is considered to support Clavel's view that dyeing takes place from a dilute, saturated aqueous solution.A study of the equilibrium distribution between fibre and dyebath of one of the more soluble disperse dyes has shown that thcre is a linear partition resembling that observed when a solute is distributed between two immiscible solvents. From the standard heat of dyeing it is inferred that two hydrogen bonds link this dye to the fibre.Cellulose acetate rayon, whilst superficially similar to viscose rayon, differs from it both physically and chemically. Viscose rayon is substantially pure cellulose, whereas in cellulose acetate rayon, consisting of " secondary " cellulose acetate, five out of every six hydroxyl groups have been repIaced by acetyl groups, which amount to about 40 % of the total weight. In consequence the fibre has a much reduced affinity for water and swells to a much smaller extent in aqueous solutions. This fact is illustrated by values for the volume term V, i.e. the volume in the water-swollen fibre available for the formation of a dye solution. Thus, Fowler and Michie 1 have assumed a volume term of 0.1 I./kg of dry cellulose acetate rayon, the corresponding figure for viscose rayon 2 being 0-45 l./kg. Similarly, Marsden and Urquhart 3 estimate the average pore size in acetate rayon to be only 5-10& whereas the corresponding figurc for viscose rayon given by Morton 4 is 20-30 A. The small diameter of the pores in acetate rayon

Linear isotherms have been obtained on viscose rayon, in the range 20-90"C, with benzidine, 0-and o-Tolidine has much higher affinity for cellulose than Non-m-tolidine, and derivatives of arninoazobenzene. the non-coplanar m-tolidine. ionic dyes do not appear t o forni aygregat,rs in aqueous solution.Heats of dyeing were found to be comtant, between 40 and 80°C.