191 1.] HINRICHS— ATOMIC WEIGHT OF VANADIUM. 193 



of the methods devised by BerzeHus which he practiced in his 

 laboratory in 1831. 



It is therefore with great astonishment that I read in the first 

 edition of the " Recalculation " of F. W. Clarke : " Roscoe's determi- 

 nation of the atomic weight of vanadium was the first to have any 

 scientific value. The results obtained by BerzeHus . . . were 

 unquestionably too high, the error being probably due to the presence 

 of phosphoric acid in the vanadic acid employed." 



The same erroneous statement is repeated identically at the 

 opening of the chapter on vanadium in the succeeding two editions 

 of the work as may be seen by comparing: p. 183. edition 1882; p. 

 211, edition 1897. and p. 305. edition 1910. 



The only new method, Cjuite recently applied to the determination 

 of the atomic weight of vanadium, is that of Edgar F. Smith. ^ 

 This admirable method strictly conforms to the Berzelian advice 

 " to chose such chemical methods for atomic weight determinations 

 that the final result shall depend as little as possible on the operator's 

 skill in manipulation."' In my summary of the work of one hundred 

 years on the determination of the atomic weight of hydrogen- I 

 have given this great rule of Berzelius. in his own handwriting, from 

 his " Sjelfbiografiska Anteckningar," published by the Kgl. Svenska 

 Vetenskapsakademien, 1901, p. 41. 



This rule requires to select such chemical reactions in which the 

 physical and chemical characters of the substances weighed are so 

 definitely fixed that the unavoidable errors of man and his instru- 

 ments become negligible quantities. Such is the reaction no. 311 

 above referred to. Hence the work done by AIcAdam in the labora- 

 tory and under the direction of Edgar F. Smith has furnished the 

 highest direct chemical approximation obtainable to the absolute 

 scientific truth that \'a is 51 exactly. This will appear, we think, 

 from a careful examination of all the results actually obtained dur- 

 ing the eighty years from 1831 to 191 1 as plotted in our two dia- 

 grams no. 730 and no. 731 published with this paper. 



The above reference to the presence of phosphoric acid in the 



' See Journal Amer. Chcm. Society. 1910, p. 1603. in the December number. 

 ■ In the Revue Generale dc Chimie. 1910, Nos. 22 and 24. 



