4 BULLETIN 122, U. S. DEPARTMENT OF AGRICULTURE. 



MOLYBDENUM. 



Hillebrand has found molybdenum to be present in the very sili- 

 ceous rocks, though in amounts too small to determine quantita- 

 tively. Demarcay 1 has detected it in the ash of the grapevine 

 and various trees, so that its occurrence in soils is possibly quite 

 common even if in very minute quantities. 



NICKEL. 



Nickel occurs associated with cobalt in certain ferromagnesian 

 rocks and in some sulphides. The amount present is very small. 

 Like copper, there may be contamination with nickel during the 

 process of analysis. Tending to an error in the opposite direction, 

 however, is the known solubility of certain of its precipitates in the 

 reagents employed. 



RUBIDIUM. 



This alkali has been reported in springs and brines. Vernadski 2 

 found it in spectroscopic traces in various feldspars and micas, and 

 PfeifTer 3 has reported it present in sugar beets and tobacco. 



THE RARE EARTHS. 



This group of elements appears to be associated with rocks high 

 in silica and possibly sodium. 



VANADIUM. 



Demarcay * and Von Lipman 4 report vanadium in the ash of the 

 grapevine, sugar beet, and various trees. It is widely distributed, 

 more especially in the basic rocks, though in small amounts. 



ZIRCONIUM. 



Zirconium occurs in largest amounts in rocks high in silica and 



sodium. It rarely amounts to 0.2 per cent and is usually less than 



0.05 per cent. Zirconium is present in soils as the silicate. A careful 



microscopic examination of any soil generally shows the presence of 



zircons. 



PREPARATION OF THE SAMPLE. 



The samples were collected from one or two spots considered 

 typical by men familiar with the soil type. One hundred pounds of 

 the surface soil, after taking off the sod, were collected, and then the 

 subsoil taken directly underneath to a depth of 3 feet when rock 

 strata did not make it impossible. Care was taken to keep the sides 

 of the hole perpendicular. Only iron tools were used in the sampling 

 and the samples were shipped in clean grain sacks. 



1 Compt. Rend., 130, 91 (1900). a Arch. Pharm. [2] 150, 97-102. 



2 Bui. Acad. St. Petersburg, 1909, 821. « Loc. cit. 



