CHEMISTRY — BAXTER. 211 



The average ratio is slightly lower than that previously found by Baxter, 

 0.849943. When combined with the ratio of silver to iodine pentoxide deter- 

 mined by Baxter and Tilley, 0.646230, the percentage of iodine in iodine 

 pentoxide is found to be 76.0355 and the atomic weights of iodine and silver 

 to be 126.913 and 107.864, respectively. This value for the atomic weight 

 of silver is in very close agreement with that recently found by Richards and 

 Willard through the analysis of lithium perchlorate, 107.871. This investi- 

 gation will be published in the Journal of the American Chemical Society, 

 vol. 32, December, 1910. 



In order to confirm the results of this research, further experiments upon 

 the ratio of the atomic weights of iodine and silver will be made by the con- 

 version of silver iodide into silver chloride. 



The analysis of phosphorus tribromide was continued by Dr. C. J. Moore. 

 (See Year Books Nos. 7 and 8.) This substance was prepared by allowing 

 pure dry bromine to react with pure dry phosphorus in a vacuum. The 

 chief difficulty in preparing the tribromide lay in the removal of the penta- 

 bromide formed by the excess of bromine which was necessarily added; for 

 to use a deficiency of bromine was found impossible, since under these cir- 

 cumstances either a lower bromide of phosphorus is produced which evapo- 

 rates with the tribromide, or else the phosphorus itself dissolves in the tri- 

 bromide and distils with it. For the same reason it was not feasible to re- 

 move the pentabromide by distillation from either red phosphorus or metallic 

 silver. Finally it was found necessary to eliminate the pentabromide by sim- 

 ple distillation in a vacuum. During the distillation the pentabromide dis- 

 sociates into tribromide and bromine, and the bromine is eliminated in the 

 first fractions of distillate. Even if it is not possible to remove the excess of 

 bromine completely in this way, the distilled material will at any rate yield a 

 minimum value for the atomic weight of phosphorus. The tribromide was 

 not exposed to air or moisture at any point in its preparation. It was col- 

 lected by distillation into small glass bulbs sealed off while exhausted. 



Several specimens of the tribromide have been prepared and have been 

 analyzed volumetrically by first decomposing the tribromide with water and 

 then titrating the hydrobromic acid produced against equivalent amounts of 

 silver, and gravimetrically by the determination of the silver bromide formed. 

 Owing to the reducing effect upon the silver salts by the phosphorous acid 

 formed in the decomposition of the tribromide with water, it was necessary 

 to oxidize the phosphorous acid by means of hydrogen dioxide, first in am- 

 moniacal solution and then in dilute nitric acid solution, before the precipi- 

 tation of the silver bromide. The material prepared and analyzed in this way 

 indicates the value for the atomic weight of phosphorus 31.03 (Ag = 

 107.870), which is identical with the value obtained by Baxter and Jones 

 from the analysis of trisilver phosphate. 



The investigation upon neodymium chloride which was carried on last 

 year by Dr. H. C. Chapin (see Year Book No. 8) has been completed by the 

 determination of the moisture in neodymium chloride dried as for analysis, 



