vi PREFACE 



introduction dealing with fundamental facts and problems ; 

 only the most incidental references will be found therefore to 

 the work of Hofmann in organic chemistry, or of van t'Hoff 

 in the various branches of physical chemistry. This limita- 

 tion is of little importance, as the advanced student will 

 find ample descriptions of the achievements and discoveries 

 of these later workers in the two volumes of Memorial 

 Lectures issued by the Chemical Society. 



In compiling the present volume, the standard histories 

 of Thomson and of Kopp have been invaluable as guides to 

 the literature, but the whole story has been written afresh 

 from the original sources. Almost without exception, every 

 reference and quotation has been checked directly in the 

 printed proofs against the original text ; if, however, any 

 errors should have survived, the author would be very grate- 

 ful to anyone who would direct his attention to them. The 

 few statements for which dates but no references are given 

 are made on the -authority of Kopp, but most of them refer 

 only to incidental points. Much of the narrative, even when 

 not enclosed between inverted commas, is in the actual 

 words of the original descriptions, a feature which the pre- 

 sent volume shares with the text-books of 100 years ago, but 

 which has gradually disappeared as the early history of 

 chemistry has become more and more a " twice-told tale." 



In order to present the material in the most accessible form, 

 quotations have been taken so far as possible from modem 

 reprints, such as those of Scheele's Essays, or the Alembic 

 Club Reprints, or from collected Works such as those of 

 Lavoisier, Davy, and Stas. To guard against anachronism, 

 full use has been made of contemporary translations of such 

 works as Bergman's Essays and Berthollet's Chemical Statics ; 

 but as the object in view was to present a picture of the 

 development of chemistry rather than a formal history, it 

 was thought better not to introduce unnecessary confusion 

 by using the name " nitric acid " when nitrogen peroxide 

 was meant, nor to obtrude at every point the various names 



