332 CARNEGIE INSTITUTION OF WASHINGTON. 



gaseous sulphuryl chloride in accordance with the equation S0 2 Cl 2 = S0 2 +Cl2. 

 This reaction has been proved to take place without the aid of catalysts in the 

 mass of the gas, and to be clearly of the unimolecular type. Thus it adds 

 another reaction of this character to the very few previously discovered; and, 

 when the experiments are completed, it will make possible further testing of 

 the various quantum radiation hypotheses that have been proposed to account 

 for the rate of chemical reactions. 



Work is also in progress on the effect of ultra-violet radiations on the rate 

 of decomposition of hydrogen iodide into hydrogen and iodine. 



With the coming of Dr. R. C. Tolman to the laboratory this autumn, 

 researches on the effect of electric discharges on the rate of chemical reactions, 

 and especially on the production and behavior of active forms of the various 

 elements, are to be undertaken by assistants working under his direction. 



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

 Continuation of exact investigation of atomic weights and other physico- 

 chemical properties of elements and of simple compounds. (For previous 

 reports see Year Books Nos. 2-20.) 



The following investigations have been in progress during the academic 

 year, some of them continuations of work begun a year or more ago. 



1. The Separation of Lead Isotopes. 



This investigation has been continued by Mr. Harold S. King, and is draw- 

 ing to a close. The various samples of different fractions of lead obtained by 

 the Grignard process and by the fractional volatilization of lead at appar- 

 ently low temperature in an X-ray vacuum are now being compared as to 

 their densities by means of a very precise method of density determination. 

 This procedure seemed likely to yield a more definite result than the deter- 

 mination of atomic weights, since the percentage accuracy of the method 

 is greater, and since the differences to be expected are very small. 



2. The Atomic Weight of Rubidium. 



Miss Edith H. Lanman, continuing the investigation upon the atomic 

 weight of rubidium, has analyzed many of her samples of extremely pure 

 rubidium chloride. The result for the atomic weight of rubidium is 85.43, a 

 value not very far from the value of Archibald. 



3. The Atomic Weight of Gallium. 



Mr. William M. Craig has completed a number of preliminary analyses 



and five final determinations of the atomic weight of gallium, by the analysis 



of gallium chloride. The result for this atomic weight is 69.716, a value 



which gives probable evidence that gallium is composed of at least two 



isotopes. A complete account of the investigation will be published in the 



near future. 



4. The Atomic Weight of Copper. 



Mr. Arthur W. Phillips has undertaken the study of the atomic weight 

 of copper, using samples of copper from widely different localities and widely 

 different geologic ages. This investigation was begun not only to verify 

 the accepted value determined thirty years ago, but also to discover if 

 widely different samples might possibly consist of different mixtures of the 

 isotopes which undoubtedly constitute this elementary substance. 



