684 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



The effect of varying compressibility is best studied in series of elements 

 possessing large compressibilities, for in these cases the variations are 

 more evident. Hence there were determined for this purpose the com- 

 pressibilities of chlorine, bromine, and iodine by Richards and Stull, and 

 of lithium, sodium, and potassium by Richards and Bonnet.* 



The values thus found, expressed in fractional decrease in volume for 

 an increase of pressure of a kilogram per square centimeter, are given 

 below : — 



The value for chlorine is only an approximation, being computed from 

 that of chloroform, carbon tetracliloride, and other analogous compounds, 

 but it is sufficiently exact for the present purpose. These values justify 

 the previous choice of chlorides, bromides, and salts of potassium in order 

 to show in as marked a fashion as possible the effects of affinity in caus- 

 ing volume change, since the three elements, chlorine, bromine, and 

 potassium, are unusually compressible. In a previous paper J the choice 

 of these three elements was made on the basis of their large coefficients 

 of thermal expansion, for this property is more or less closely associated 

 witii compressibility, as the rule of Dupre § indicates. 



A cursory study of the above table of compres.sibilities leads one im- 

 mediately to predict that, with a given affinity, a greater change in 

 volume would be caused in the formation of a salt of potassium than 



* Of these investigations the first lias already been printed in Publication No. 7 

 of the Carnegie Institution of Washington, and the second will soon appear in the 

 same series. 



t The specific gravities of- these three alkali-metals were determined by 

 Richards and P.onnet, and will soon be published. 



t Richards, These Proceedings, 37, 399 (1902). 



§ See, for example, Ostwald, Lehrbuch, 1, 394 (1891). 



