progress in chemistry. 239 



"atomic weights." 



The determination of these ''constants of nature" was at once fol- 

 lowed out by many chemists, Thomson among- the first. But chief 

 among- the chemists who have pursued this branch of work was Jacob 

 Berzelius, a Swede, who devoted his long life (1779-1848) to the manu- 

 facture of compounds and to the determination of their composition, 



or. as it is still termed, the determination of the "atomic weights" 



more correctly, "equivalents'" — of the elements of which they are 

 composed. It is to him that we owe most of our analytical methods, 

 for prior to his time there were few, if any, accurate analyses. 

 Although Lavoisier had devised a method for the analysis of com- 

 pounds of carbon, viz, l)v Inirning the organic compounds in an 

 atmosphere of oxygen contained in a bell jar over mercury and meas- 

 uring the volume of carbon dioxide produced, as well as that of the 

 residual oxygen, Berzelius achieved the same results more accurately 

 and more expeditiously by heating the substance, mixed with chlorate 

 of potassium and sodium chloride, and then estimating the hydrogen 

 as well as the carl)on. This process was afterwards perfected by Liebig. 

 Berzelius, however, was able to show that compounds of carbon, like 

 those of other elements, were instances of coml)ination in constant and 

 nudtiple proportions. 



In 1815 two papers were published in the Annals of Philosoph}' 

 l)y Dr. Prout which have had nmch influence on the progress of 

 chemistry. They dealt with the figures which were being obtained 

 by Thomson, Berzelius and others, at that time supposed to represent 

 the '"atomic weights" of the elements. Prout's hypothesis, based on 

 only a few numbers was that the atomic weights of all elements were 

 nuiltiples of that of hydrogen, taken as a unity. There was nmch 

 dispute regarding this assertion at the time, but as it was contradicted 

 by Berzelius's numbers the balance of opinion was against it. But 

 about the year 1840 Dumas discovered an error in the number (12.12) 

 given by Berzelius as the atomic weight of carbon; and with his collab- 

 orator, Stas, undertook the redetermination of the atomic weights 

 of the commoner elements — for example, carbon, oxygen, chlorine, 

 and calcium. This line of research was subsequently pursued alone 

 by Stas, whose name will always be remembered for the precision 

 and accuracy of his experiments. At first Dumas and Stas inclined 

 to the view that Prout's hypothesis was a just one, but it was com- 

 pletely disproved by Stas's subsequent work, as well as by that of 

 numerous other observers. It is nevertheless curious that a nmch 

 larger proportion of the atomic weights approximate to whole num- 

 bers than would be foretold by the doctrine of chances, and perhaps 

 the last has not been heard of Prout's hypothesis, although in its orig- 

 inal crude form it is no longer worthy of credence. 



