CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 



HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OF CHROMIUM. 



FIRST PAPER. — THE ANALYSIS OF SILVER CHROMATE. 



By Gregory Paul Baxter, Edward Mueller, and 

 Murray Arnold Hines. 



Presented January 13, 1909. Received December 11, 1908. 



Introduction. 



The following table 1 gives the results of investigations upon the 

 atomic weight of chromium from the time of Berzelius, recalculated 

 with the use of recent atomic weight ratios upon the basis of silver 

 (107.88) and oxygen (16.000). 2 



The value chosen by the International Atomic Weight Committee, 

 52.1, which is based chiefly upon the more recent determinations, 

 seems to be fairly close to the truth, with an uncertainty of one tenth 

 of a unit. 



It has been repeatedly shown, especially in this laboratory, that 

 most of the earlier work upon atomic weights has been vitiated by 

 neglect of certain fundamental precautions. The incomplete drying of 

 solids has been responsible for many of the discrepancies and errors 

 which exist. Neglect of the solubility of precipitates, together with 

 the use of too concentrated solutions during precipitation, so that 

 perceptible inclusion and occlusion took place, undoubtedly have 

 influenced many gravimetric processes. Volumetric processes have 

 been affected by inaccurately prepared standard solutions, as well as 

 the difficulty inherent in measuring exactly large volumes of solution. 



In discussing in detail the applications of the above causes of con- 

 stant error to the individual investigations, at the best it is only pos- 



1 Clarke, A Recalculation of the Atomic Weights, Smith. Misc. Coll., 1897. 



2 The following atomic weights are used in the recalculation of the older 

 values: Ag = 107.88; CI = 35.457; Pb = 207.09; N = 14.01; Ba = 137.37; S = 

 32.07; H= 1.008; K = 39.095; As = 74.96; 1 = 126.92. The values of Rawson 

 and Meineke are reduced to the vacuum standard; the others are not so 

 corrected. 



vol. xliv. — 26 



