(i) The significance of the "plastic" state, in relation to the properties of blast furnace coke, is discussed and the importance of swelling pressure is emphasised. (ii) The aims of the investigation are drawn up. They include the development of a method, using di-electric heating, for the measurement of the swelling pressure of "plastic" coals and the study of the variation of this property with coal rank, etc. (iii) Previous methods of measuring swelling pressure are reviewed and their sources of error indicated. (iv) The theory of di-electric heating is described and the possibility of this technique giving uniform volume heating, in a coal sample is put forward. (v) The experimental apparatus is described. (vi) A detailed account of the development work entailed in the application of this novel technique is given. The most striking point arising from the development work is the critical effect of small amounts of oxygen in reducing the swelling properties of a coal. (vii) The finally adopted experimental method is described The results are presented in the following four sections, viz:- (a) Swelling Pressure - Swelling Volume relationship for a Durham (Sacriston) coal by a "constant volume" method. Swelling Pressure - Swelling Volume relationship for a Scottish (Kingshill) coal by a "constant pressure" method. (c) Swelling Pressure - Swelling Volume relationship for the Durham coal by a "constant pressure" method (d) An investigation of swelling mechanism. (viii) Recent work on the physico-chemical nature of coal and carbonised coal is reviewed in so far as it is relevant to the investigation. (ix) The results of (d) paragraph (vii), are discussed and compared with previous similar investigations. (x) The swelling pressure-swelling volume relationships obtained by the "constant pressure" method, are analysed. Specific permeability figures are deduced therefrom and the variation of these with pressure, temperature and volume, for the two coals tested, is discussed. An analysis of the swelling pressure-swelling volume relationship, obtained by the "constant volume" method, indicated that little useful information could be deduced from this complex relationship
