Wells S Foote — One Hundred Years of Chemistry. 263 



the adoption of oxygen as exactly 16 as the basis, which 

 gives hydrogen the valne of 1-008. 



As early as 1815, Pront, an English physician, had 

 advanced the view that hydrogen is the primordial sub- 

 stance of all the elements, and consequently that the 

 atomic weights are all exact multiples of that of hydro- 

 gen. This hypothesis has been one of the incentives to 

 investigations upon atomic weights, for it has been found 

 that these constants in the cases of a considerable num- 

 ber of the elements are very close to whole numbers 

 when based upon hydrogen as unity, or even still closer 

 when based upon oxygen as 16. 



"With our present knowledge Prout's hypothesis may 

 be regarded as disproved for nearly all the elements 

 whose atomic weights have been accurately determined, 

 but the close or even exact agreement with it in a few 

 cases is still worthy of consideration. There is an inter- 

 esting letter from Berzelius to B. Silliman, Jr., in the 

 Journal (48, 369, 1845) in which Berzelius considers the 

 theory entirely disproved. 



For a long time entire reliance was placed upon the 

 atomic weights obtained by Berzelius, but it came to be 

 observed that the calculation of carbon from carbon diox- 

 ide appeared to give high results in certain cases, so that 

 doubt arose as to the accuracy of Berzelius 's work. Con- 

 sequently in 1840 Dumas, assisted by his pupil Stas, made 

 a new determination of the atomic weight of carbon, and 

 found that the number obtained by Berzelius, 12-12, was 

 slightly too large. Subsequently Dumas determined 

 more than twenty other atomic weights, but this great 

 amount of work did not bring about any considerable 

 improvement, for it appears that Dumas did not greatly 

 excel Berzelius in accuracy, and that the latter had made 

 one of his most noticeable errors in connection with 

 carbon. 



Soon after assisting Dumas in the work upon carbon, 

 Stas began his very extensive and accurate, independent 

 determinations, leading to the publication of a book in 

 1867 describing his work. Stas made many improve- 

 ments in methods by the use of great care in purifying 

 the substances employed, and especially by using large 

 quantities of material in his determinations, thus dimin- 

 ishing the proportional errors in weighing. His results, 



