By chance, the second volume of this work, namely that in which the reversible systems are treated, appeared in 1949, and now the work has been completed by the appearance of the first volume in which irreversible systems are dealt with. In the second volume I wrote a Preface, which is now, in the main, repeated, thus acting as an introduction to both volumes. -
The need for a collective work en the science of colloids formed a subject of discussion between the publishers of this work and myself shortly before the outbreak of the Second World War. The first preparations were brought to an end by the worid events, in view of the fact that ai! possibility of contact with foreign colleagues had been broken. When the war continued year after year, the question arose whether we could restrict ourselves to Dutch collaborators and in 1944 I sent a request to a number of my fellow-countrymen to take this work in hand. It was immediately apparent that this р!дп was receive' with enthusiasm and most of those who now collaborate m this work met to devise a plan of campaign; a few others, whom we invited to do so, joined us later.