PREFACE This treatise is intended to give the student and the general reader such an insight into the natural laws and physical principles underlying the production, transmission and use of com- pressed air, as shall enable him to comprehend the operation of the various appliances employed for this purpose and to judge of their merit. -No attempt has been made to present in this book an extensive description of all the existing types of compressors or of the countless appliances using compressed air. The authors chief aim was to provide the student, who is interested in technical questions concerning the operation as well as the construction of compressors and air engines, with a background of understand- ing that will enable him, not only to solve the many theoretical problems connected therewith, but to make independent research into the seemingly unlimited possibilities of compressed air. The territory still unexplored is vast and full of promises to the intrepid explorer who enters the field with a thorough knowledge of all the truths discovered, as well as the pitfalls encountered, by those who have gone before him. The numerous, carefully selected problems constitute what the author believes to be one of the strong features of this book. If ever any doubt lingers in the students mind as to the mean- ing of certain principles or laws presented in the text and their practical application, a numerical problem will, as a rule, remove the doubt and make clear the meaning. Moreover, such problems make the student familiar with actual quantities, never revealed by mere formulas quantities which are often startling to the uninitiated and impress him with the practical value of such formulas more forcibly then the mere text can do. The author has endeavored to bring the work well within the comprehension of the average technical student who has a sound knowledge of the elements of algebra, physics and me- chanics. Higher mathematics were used sparingly and only when they led to a simpler solution of certain problems. To the advanced reader some of the deductions contained in the book may appear unnecessarily lengthy. It has been the writers experience, however, that many of the difficulties encountered by students arise from a misunderstanding of facts which, although perfectly obvious to one who has mastered the subject, remain nevertheless obscure to the beginner unless explained from various points of view and by analogy with facts already familiar to him. In preparing this treatise the writer has made free use of the rather scattered and by no means voluminous literature on the subject of compressed air. His debt to all who have labored in this field before him can hardly be acknowledged adequately by the mere mentioning of their names. He has therefore refrained from referring in the text to such names but wishes to express in this preface his gratitude to all authors and investigators from whose writings he has drawn both inspiration and information. Throughout the preparation of this work the author had the untiring assistance of President C. H... --This text refers to an alternate Paperback edition.