PREFACE 



THESE Essays on Chemical History and Biography, and on 

 chemical topics, have been delivered as lectures, or pub- 

 lished as magazine articles at various times in the course 

 of the last twenty-five years. A little alteration has been 

 necessary to avoid undue repetition, and in some cases 

 footnotes have been added, to correct statements which 

 have been rendered inaccurate by the progress of dis- 

 covery. 



I have to thank the University of Glasgow for permis- 

 sion to reprint the oration on Black ; the editor of the 

 Youth's Companion for permission to reprint the sketch 

 of Lord Kelvin, ' What is an Element ? ' ' On the Periodic 

 Arrangement of the Elements,' 'Radium and its Pro- 

 ducts,' ' What is Electricity ? ' and ' How Discoveries are 

 Made ' : the editor of the Contempora/^y Review for 

 permission to reprint the article on * The Becquerel Rays ' : 

 and the Royal Society, which has kindly granted similar 

 permission to republish the life of M. Berthelot. 



WILLIAM RAMSAY. 



October 1908. 



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