80 PROGRESS OF SCIENCE IN THE CENTURY. 



touch-stone for chemistry; it supplied a quantitative 

 test by which the accuracy of research could be con- 

 tinually judged. 



THE ATOMIC THEORY. 



Before Dalton. The great chemist Berzelius, 

 following his predecessor Richter, quotes on the first 

 page of his classic treatise on Chemical Proportions 

 the verse from the Book of Wisdom which says : 



Omnia in mensurd et numero et pondere disposuisti. 

 Thou hasfc ordered all things in measure and number and 

 weight. Sap. XI. 21. 



This may be regarded by some as expressing a re- 

 markable prevision of one of the great results of 

 chemical science, that exact quantitative relations 

 are always implied in qualitative changes of sub- 

 stance. But whether it was a prevision or not, the 

 verse quoted found no scientific commentary till 

 towards the end of the eighteenth century, and the 

 commentary then begun is still in progress. 



The invention of accurate balances like Lavoi- 

 sier's made it possible to pass beyond the detection 

 of chemical elements to some understanding of ma- 

 terial architecture. And there seem to have been 

 many who were simultaneously pondering over the 

 problem. Thus Jeremias Benjamin Richter, a math- 

 ematical chemist born before his time, published in 

 1792-1794 a treatise on Stoicheiometry, or " the art 

 of measuring chemical elements," in which he showed 

 that acids and bases combine in definite quantita- 

 tive proportions to form neutral salts. About the 

 same date Proust drew the familiar distinction be- 

 tween chemical mixtures and chemical compounds, 

 pointing out that the latter are characterised by quite 

 definite proportions, whether formed artificially in 



