JOHN D ALT ON 509 



stituents in fixed and invariable proportions." Notice, in the words 

 I have italicized, the unanimous trend towards quantitative measure- 

 ments and accuracy, the ruling notion being that of numerical ratio. 

 We come to closer quarters with our central theme in the work of 

 Eichter (1762-1807), an investigator, it is important to note, obsessed 

 by mathematical methods. Despite his obvious idiosyncrasy, Eichter 

 arrived at the law of equivalent ratios — " The qualities of acids and 

 bases equivalent in one neutralization are equivalent in all." In 1802 

 Fischer made Eichter's conclusions known to Berthollet, and chemical 

 ratios became an integral part of the science. As Wollaston says, in 

 1814: 



It is to Richter we are originally indebted for the possibility of represent- 

 ing the proportions in which the different substances unite with each other in 

 such terms that the same substance shall always be represented by the same 

 number. He discovered the law of permanent proportions. 18 



The experimental proof was clinched by Berzelius in 1811-12, and 

 the law of " permanent " or " definite " ratios, as it is called now, put 

 the problem of composition on a practicable footing. 19 It should be 

 noted also that, in stating the numerical values of the elements, Dalton 

 employed some determinations of other chemists, at all events as checks. 



We are now in a position to see that series of complicated researches, 



all looking to quantitative results, furnished Dalton with material which 



enabled him to render the atomic theory perspicuous and applicable 



from the very outset. Notwithstanding, to him must be given sole 



credit for the final simplification, which had been exercising his mind 



for some eighteen years — since 1790, in fact. A quotation from Ber- 



thollet's " Essai" (1803) may suffice to emphasize the long step due to 



Dalton's insight. 



Some chemists, influenced by having found determinate proportions in sev- 

 eral combinations, have frequently considered it as a general law that combina- 

 tions should be formed in invariable proportions; so that, according to them, 

 when a neutral salt acquires an excess of acid or alkali, the homogeneous 

 substance resulting from it is a solution of the neutral salt in a portion of the 

 free acid or alkali. This is a hypothesis which has no foundation, but a dis- 

 tinction between solution and combination. 20 



Undoubtedly, events tended towards the new climate of opinion, 

 nay, this had become so far prevalent that the Irishman, William Hig- 

 gins (17P-1825) came nigh playing Wallace to Dalton's Darwin. 

 Indeed, in 1814, he raised a claim to priority, which was disproved at 

 once by Thomson, the Glasgow chemist who had made Dalton known. 

 This Higgins is to be distinguished from his uncle, Bryan Higgins 



18 The italics are mine. 



19 Reference should be made to the classical experiments in further con- 

 firmation by Stas (1865). 



2 " Cf. Lambert's English translation, p. 39. 



