CHEMISTRY. 353 



balance suspended in a large glass desiccator containing dilute 

 sulphuric acid and varying the concentration of this acid, whose 

 water- vapor- pressure is well known, till the salt-hydrate neither loses 

 nor gains weight. Another method consists in shaking the salt- 

 hydrate with an organic solvent (amyl alcohol) till it becomes saturated 

 with water from the hydrate and then determining the water-content 

 of the solvent, to which corresponds a certain known water-vapor- 

 pressure. 



A research has also been started by Dr. W. N. Lacey on the hydroly- 

 sis at 100° of ammonium salts of very weak acids, such as carbonic 

 acid, with the view of extending our knowledge of the ionization of 

 such acids (which is confined to the neighborhood of the room temper- 

 ature) to higher temperatures. 



Richards, Theodore W., Harvard University, Cambridge, Massachusetts. 

 Continuation of exact investigations of atomic weights and other physico- 

 chemical properties of eleme7its and simple compounds. (For previous 

 reports see Year Books Nos. 2-14.) 



The following investigations have been conducted during the pa«t 

 academic year with the assistance of this grant, employing also 

 permanent apparatus purchased with previous grants as well as with 

 funds of the university. 



1. The Atomic Weight of Isotopic Lead. 



This research, conducted with the help of Dr. Charles Wadsworth 

 3d and Norris F. Hall, was a continuation of that begun three years 

 ago with the assistance of Dr. Lembert.^ The acquisition of a large 

 quantity of Australian isotopic lead, through the kindness of Mr. 

 Bubb of the Radium Hill Company, and the cooperation of Mr. S. 

 Radcliff, made possible a valuable extension of the work. This sample, 

 because of its large quantity, could be more thoroughly freed from 

 common impurities than the smaller samples previously employed; 

 and it was recrystallized as nitrate and chloride until its ultra-violet 

 spectrum (photographed by Professor Baxter) and its visible spec- 

 trum as far as wave-length 7600 (photographed on orthochromatic 

 plates and studied visually in a Hilger spectrometer) showed no trace 

 of any line foreign to ordinary lead prepared by Baxter in the highest 

 degree of purity. Nevertheless, the atomic weight of this substance 

 was found to be as low as 206.35 (instead of 207.19) and this low 

 value was not altered by continued purification, as far as we have 

 yet been able to pursue it. Another especially valuable sample, 

 obtained from pure selected crystals of Norwegian cleveite through 

 the kindness of Dr. Ellen Gleditsch of Kristiania, gave the atomic 

 weight 206.085, the lowest yet found by us, and almost as low as the 

 lowest found by Dr. O. Honigschmid, who has confinned our results. 



'See previous Year Books 



