312 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



Berzelius's work on equivalents. The importance of 

 Richter's observations was realised, perhaps for the first time, 

 by Berzelius, who writes : 



" It follows from the researches of Richter, that from 

 good analyses of a few salts, one could calculate with 

 precision the composition of all the others. 



"I formed [in 1807] the project of analysing a series of 

 salts, with the idea that it would be superfluous to examine 

 the others." Thus 



"It is evident that if analyses are made of all the salts 

 formed by one acid, for instance, by sulphuric acid with all 

 the bases, and of those formed by one base, for example 

 baryta with all the acids, one would have the necessary 

 data to calculate the composition of all the salts formed by 

 double decomposition, provided that they retained their 

 neutrality" (Chemical Proportions, 1819, 16). 



To Berzelius belongs the credit of having done more 

 than any of his contemporaries to provide the data whereby 

 the composition of a large range of compounds might be 

 calculated from the results of a few careful analyses, not 

 merely in the case of acids, bases and salts, but throughout 

 the whole field of chemical combination. 



The proportions by weight in which elements and com- 

 pounds interact with one another are described as their 



EQUIVALENTS Or COMBINING WEIGHTS. As these weights 



are all relative, some standard has to be selected to 

 take the place of the r,ooo parts of sulphuric acid used 

 above in summarising Richter's data. 



Dalton selected one part of hydrogen, whilst Berzelius 

 preferred one hundred parts of oxygen. The standard used 

 at the present time is eight parts of oxygen, so that " The 

 equivalent of an element is that weight which combines with 

 eight parts by weight of oxygen" 



The choice of oxygen instead of hydrogen as the stan- 

 dard has the practical advantage that all the elements 



