PREFACE TO THE FOURTH EDITION SEVERAL changes in the text, and additions thereto have been made by the Author in preparing the sixth German edition. These changes and additions have been put into their proper places in this the fourth English edition. CAMBRIDGE, September 1908. M. M. P. M. PREFACE TO THE THIRD EDITION THE Author has been so good as to supply a few additions, designed by him to make the book of more general interest, and to bring it up to date these have been put into their proper places in the text. He has also allowed me to see his corrected proofs for the fourth German edition. I have ventured to make a few small changes these have been submitted to Professor Lassar-Cohn, and approved by him. CAM-BRIDGE, November 1904. vii M. M. P. M. PREFACE TO THE FIRST EDITION THIS book, which now appears in English, embodies the substance of a course of lectures delivered by Dr. Lassar- Cohn, Professor of Chemistry in the University of Konigs- berg, to a society Humboldt Academy in that town modelled on the celebrated of Berlin. These lectures, and the publication of them in book form, caused quite a stir in German circles. And it is in the hope that they will prove at once interesting, instructive, and suggestive to English readers that I have prepared a translation at the request of the publishers. That the lectures cover a great variety of topics will be evident from a glance at the Table of Contents. The method of treatment is eminently human and sugges- tive. The author shows that chemical phenomena are intimately bound up with our daily lives, and that whether we are conscious of it or not we are constantly carrying on chemical operations. He also brings home to us how chemical considerations play their part in those speculations regarding the physical universe that are suggested by each fresh discovery made by science. Vague notions circulate in mens minds concerning chemistry. Some think the chemist is a man who com- pounds drugs and mixes pills and others look on him as an astrologer of the modern sort. This book shows that the chemist is in a sense both of these, and much more than both it causes the careful reader to realise the per- meating nature of chemical knowledge, and it teaches him that chemistry is emphatically the most human, and for that reason the most fascinating, of the sciences. The book can be followed intelligently by any reader who gives it a little care no special technical knowledge is required. The translation has been made from a copy of the original book kindly lent by the Author containing Dr. Lassar-Cohns corrections and additions. The very few additions made by the Translator are inclosed in square brackets. CAMBRIDGE, May 1896. M. M. P. M...