In the present volume the authors have attempted to emphasise those aspects of the subject which are of special importance to such students, while others have been treated in sufficient detail to enable the general principles to be securely grasped. In order to avoid the mischievous tabula tion of disconnected facts, matters of purely technical interest have been as far as possible omitted from the text; but numerous footnotes have been added, pointing out the application of the general principles to commercial and industrial processes. These notes should add to the interest of the work and, to a certain extent, give point to the students' reading.
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