that about 100 journals are required to yield fifty In 1957, the Thermophysical Properties Research Center (TPRC) of Purdue University, under the percent. But that other fifty percent! It is scattered leadership of its founder, Professor Y. S. Touloukian, through more than 3500 journals and other docu began to develop a coordinated experimental, ments, often items not readily identifiable or ob theoretical, and literature review program covering tainable. Over 75,000 references are now in the files. a set of properties of great importance to science and technology. Over the years, this program has grown Thus, the man who wants to use existing data, steadily, producing bibliographies, data compila rather than make new measurements himself, faces tions and recommendations, experimental measure a long and costly task if he wants to assure himself ments, and other output. The series of volumes for that he has found all the relevant results. More often which these remarks constitute a foreword is one of than not, a search for data stops after one or two these many important products. These volumes are a results are found-or after the searcher decides he monumental accomplishment in themselves, re has spent enough time looking. Now with the quiring for their production the combined knowledge appearance of these volumes, the scientist or engineer who needs these kinds of data can consider himself and skills of dozens of dedicated specialists. The Thermophysical Properties Research Center de very fortunate.