274 



Prof. W. J. Sollas. 



molecular weight is 58-513 (Na 23'06 + 0135-453).* Its density, 

 corresponding to the specific gravity, found as the result of very 

 careful determinations by Retgers, is 2'167 at 17 C. The gross 

 volume is then 58'513/2'167 = 27'0002. If this number be multi- 

 plied by 4, it will give the volume of a primitive cubelet, supposed 

 to be built up of 4 molecules, as already described. The cube root of 

 this number (108*01) is 4' 7623, and represents the length of an 

 edge of the cubelet, or the sum of the diameters of the atoms of 

 sodium and chlorine, by which this edge is determined. The next 

 step is to endeavour to obtain some probable value for the ratio of 

 these diameters, that of the sodium to that of the chlorine atom. 



It is quite certain if the sodium and chlorine atoms do not both 

 occupy the same space, that the volume of sodium, and the other alkali 

 metals, is very different in the free state and in combination. This 

 is a conclusion to which Kopp was led, who found that by assuming 

 a reduction of the volume in the free state to one-half when the 

 element entered into combination, he obtained fairly constant dif- 

 ferences on subtracting the half volumes of the metals from the 

 volumes of the chlorine salts. Our investigations support this 

 opinion of Kopp. In the following table data for investigation are 

 given for such haloid compounds as are open to study. 



Metals. 

 Lithium . 



Sodium 23-06 



Potassium.. 39 '14 



m, atomic weight ; c?, density ; Y, gross volume ; T, temperature at 

 which sp. gr. was determined ; F, fusion point. 



Salt. m. d. Y. T. 



Lithium chloride. . 

 Sodium chloride . 

 Potassium chloride 

 Lithium bromide. . 

 Sodium bromide . . 







Potassium bromide 

 Lithium iodide 

 Sodium iodide 

 Potassium iodide. . 

 



* In this and all subsequent cases the atomic weights are those given by Ostwald 

 to oxygen, 16, as a base. 



