156 HISTORY OF CHEMISTRY. 



relations. Thus, sulphur, combined with oxygen in 

 two different proportions, forms two acids, the sul- 

 phuYous and the sulphuric; and these acids form, 

 with earthy or alkaline bases, sulphas and sulph- 

 ates ; while sulphur directly combined with another 

 element, forms a suliphuret. The term oxyd (now 

 usually written oxide,} expressed a lower degree of 

 combination with oxygen than the acids. The Me- 

 thode de Nomenclature Chimique was published in 

 1787; and in 1789, Lavoisier published a treatise 

 on chemistry in order further to explain this me- 

 thod. In the preface to this volume, he apologizes 

 for the great amount of the changes, and pleads the 

 authority of Bergman, who had exhorted De Mor- 

 veau " to spare no improper names ; those who are 

 learned will always be learned, and those who are 

 ignorant will thus learn sooner." To this maxim 

 they so far conformed, that their system offers few 

 anomalies; and though the progress of discovery, 

 and the consequent changes of theoretical opinions, 

 which have since gone on, appear now to require 

 a further change of nomenclature ; it is no small 

 evidence of the skill with which this scheme was 

 arranged, that for half a century it was universally 

 used, and felt to be far more useful and effective 

 than any nomenclature in any science had ever 

 been before. 



