PREFACE 



IN the preparation of this volume the purpose has been 

 to present an historical account of the more important facts 

 and theories of chemistry, as these disclosed themselves to 

 the original workers in this branch of science. No attempt 

 has been made to write a formal History of Chemistry, 

 either as a survey of the various periods into which the 

 history of the science may be divided, or in the more usual 

 biographical form. The material has been classified by 

 subjects rather than by authors ; but it will be found that 

 under this system the work of individual experimenters is 

 described quite as fully as in a biographical survey, whilst 

 in the case of certain chemists, such as Priestley, Lavoisier 

 and Gay-Lussac, it has been possible to include detailed 

 descriptions of experimental work which could scarcely have 

 found a place in a brief biography. 



The Biographical Index provides a key to the work of 

 each author as it is described in the text, and contains most 

 of the essential items for an account in narrative form of 

 the achievements of the great pioneers of chemistry. 



In a few cases this index contains dates and titles of works 

 not included in the text, as, for example, Cavendish's work 

 on the density of the earth, and some of Faraday's physical 

 experiments ; but no attempt has been made either in the 

 biographical index or in the text to record the later and 

 more detailed developments of organic or of physical chem- 

 istry. Such a record would be out of place in a historic?^ 



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