58 CLARKE AND STEIGERI METALLIC ELEMENTS 



recorded in this paper. This question of the purity of the elec- 

 trolyte has received less attention from previous observers than 

 it deserves. We have described our methods for purifying silver 

 nitrate in Part III of this series of papers. 



GEOLOGY. — The relative abundance of several metallic elements. 

 F. W. Clarke and George Steiger,U.S. Geological Survey. 



During the past twenty-five years, several estimates of the 

 relative abundance of the commoner chemical elements have been 

 published from the laboratory of the United States Geological 

 Survey. 1 These estimates, however, covered only such consti- 

 tuents of the earth's crust as are usually determined in the course 

 of fairly complete analyses; including, in many cases, the less im- 

 portant elements barium, strontium, nickel, chromium, vanadium 

 and zirconium. For the more familiar metals, copper, lead, zinc 

 and arsenic, no really adequate data were available ; and no attempt 

 was made to compute either their abundance or their frequency. 

 Such attempts have been made by others, however, but not alto- 

 gether conclusively. - 



In order to gain a definite idea as to the relative abundance of 

 the elements in question, a number of composite analyses were 

 made. That is, in each group of substances investigated, many 

 samples were blended into one uniform sample, and that was then 

 analyzed. The average content of each metal was determined 

 in that way with as close an approximation to accuracy as could 

 have been attained by many individual analyses. Four such 

 composites have been studied thus far; namely, two of oceanic 

 clays, contributed by Sir John Murray;^ one of silt or mud from 

 the delta of the Mississippi; and one of igneous rocks which had 

 previously been analyzed in the laboratory of the Survey. For the 

 the Mississippi silt the general analysis, not heretofore published, 

 is as follows:"* The composite was made up of 235 separate sam- 



^ For the latest of these estimates see Survey Bulletins 419 and 491. Also a 

 paper in Proc. Amer. Phil. Soc, 51, 214. 



2 See for example Vogt, Zeitsch. prakt. Geol., 1S9S, pp. 225, 314, 377, 413, and 

 1899, pp. 10, 274; and Kemp, Econ. Geol., 1, 207. 



' For the complete analyses of these clays see Journ. Geol., 15, 783. 



* Except when otherwise stated the analyses given here were made by Mr. 

 Steiger. 



