118 THE ATOMIC WEIGHTS. 



ing any importance was that of Berzelius,* in 1818 and 

 1826, which led to results much in excess of the correct 

 figure. His method consisted in precipitating a known 

 weight of lead nitrate with an alkaline chromate and weigh- 

 ing the lead chromate thus produced. The error in his de- 

 termination arose from the fact that lead chromate, except 

 when thrown down from very dilute solutions, carries with 

 it minute quantities of alkaline salts, and so has its apparent 

 weight notably increased. When dilute solutions are used, 

 a trace of the precipitate remains dissolved, and the weight 

 obtained is too low. In neither case is the method trust- 

 worthy. 



In 1844 Berzelius' results were first seriously called in 

 question. The figure for chromium deduced from his ex- 

 periments was somewhat over 56 ; but Peligott now showed, 

 by his analyses of chromous acetate and of the chlorides of 

 chromium, that the true number was near 52.5. Unfortu- 

 nately, Peligot's work, although good, was published with 

 insufficient details to be useful here. For chromous acetate 

 he gives the percentages of carbon and hydrogen, but not 

 the actual weights of salt, carbon dioxide, and water from 

 which they were calculated. His figures vary considerably 

 moreover ; enough to show that their mean would carry but 

 little weight when combined with the more explicit data 

 furnished by other chemists. 



Jacquelain'sl work we may omit entirely. He gives an 

 atomic weight for chromium Avliich is notoriously too low, 

 and prints none of the numerical details upon which his 

 result rests. The researches which particularly command 

 our attention are those of Berlin, Moberg, Lefort, Wilden- 

 stein, Kessler, and Siewert. 



Among the papers upon the atomic weight under consid- 

 eration that by Berlin is one of the most important. |i His 

 starting point was normal silver chromate ; but in one ex- 



* Schweigg. Journ., 22, 53, and Poggend. Annal., 8, 22. 

 t Compt. Rend., 19, 609 and 734; 20, 1187 ; 21, 74. 

 + Compt. Rend., 24, 679. 1847. 

 II Journ. fur Pralct. Chem., 37, 509. and 38, 149. 1846. 



