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 * 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. 
RUBIDrUM. 
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 1 and Yon 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 hi the sampling 
and the samples were shipped in clean grain sacks. 
• Compt. Rend., 130, 91 (1900). 3 Arch. Pharm. [2] 150, 97-102. 
2 Bul. Acad. St. Petersburg, 1909, 821. 4 Loc. cit. 
