CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OF PHOSPHORUS. 



FIRST PAPER.— THE ANALYSIS OF SILVER PHOSPHATE. 



By Gregory Paul Baxter and Grinnell Jones. 



Presented September 28, 1909. Received November 12, 1909. 



Although phosphorus is one of the best known and most important 

 elements, present knowledge concerning its atomic weight is somewhat 

 inadequate. The early determinations of this constant by Dulong, 1 

 Pelouze, 2 Berzelius, 3 and Jacquelain 4 are widely discrepant and have 

 no particular significance. Those by Schrotter, Dumas, van der Platts, 

 and Berthelot, on the other hand, all give values not far from 31.0, and 

 this value has been selected by the International Committee on Atomic 

 Weights. Although these investigations have already been critically 

 discussed by Clarke, 5 Brauner, 6 and others, a few of the more important 

 sources of error are briefly pointed out here. 



Schrotter, 7 the discoverer of red phosphorus, converted weighed 

 quantities of this substance into phosphorus pentoxide by combustion 

 in a stream of oxygen. As the mean of ten determinations which 

 varied from 30.94 to 31.06, he obtained 31.03 for the atomic weight of 

 phosphorus. The oxygen used was slightly moist, as Brauner has 

 pointed out, since, although it was dried by phosphorus pentoxide, it 

 was finally passed through a tube containing calcium chloride ! The 

 phosphorus pentoxide formed during the combustion must have re- 

 tained this small amount of water, which would make the atomic 

 weight of phosphorus appear too low. Schrotter admits that the com- 

 bustion was incomplete, and since this error would tend to raise the 

 atomic weight of phosphorus, he concludes that the true value is 

 31.00. 



1 Ann. Chim. Phys. 1816, 2, 149. 2 C. R.. 1845, 20, 1053. 



3 Lehrbuch, 5th Ed., 1845. 3, 1188. 4 C. R., 1851, 33, 693. 



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



6 Abegg, Handb. der anorg. Chem., 1907, vol. 3, part 3, p. 366. 



7 Ann. Chim. Phys., (3), 1853, 38, 131. 



