8 BULLETIN 122, U. S. DEPARTMENT OF AGBICULTUBE. 
duced with hydrogen. The chlorides of the rare alkalies, together 
with a comparatively large amount of potassium chloride, were 
washed through with hot water into a very small dish, evaporated 
to dryness, taken up, and filtered off with 3 portions of 4 drops each 
of strong hydrochloric acid. By this method 0.0001 gram of rubidium 
or caesium mixed with 10 grams of soil could easily be separated and 
identified. The method of Gooch and Phinney x for the identification 
with the spectroscope was followed. On account of the large 
amount of potassium present, quantitative refinement was not at- 
tempted, though the results obtained are given in four magnitudes. 
These magnitudes were obtained by comparison with four known 
amounts of rubidium treated in exactly the same manner as the soils 
tested. 
PHOSPHORIC ACID. 
Considerable difficulty was experienced in getting concordant results 
with this determination. The phosphoric acid solution was obtained 
in two ways — by fusion with sodium carbonate and solution in nitric 
acid and by decomposition with hydrofluoric and nitric acids. Both 
methods yield results which agree well. The main difficulty seems to 
be in preventing the separation of a flocculent precipitate, either from 
the solution or from the glass which may be attacked by the am- 
moniacal solution. This flocculent precipitate increases on standing. 
Woy's 2 method of weighing the gently ignited molybdate precipitate 
gives results slightly lower than the magnesia method, though it may 
be as near the truth when the amount of vanadium in the soil is small. 
OTHER ELEMENTS. 
The results for barium, manganese, strontium, zirconium, and 
chromium were sharp and clear cut and are believed to be reliable. 
The vanadium determinations, however, were somewhat uncertain as 
to absolute amount, though confirmatory tests with hydrogen per- 
oxide and nitric acid showed the element to be present in all cases 
and showed a depth of color proportional to the amount found by 
titration. 
Throughout the work double precipitations were performed, except 
in special instances, and blanks were made in all cases. The correc- 
tions for calcium and magnesium in the reagents and that derived 
from the solubility of the glass were quite large, considering the 
amounts present in the soil. Evaporation, precipitations at the boil- 
ing point, etc., were made in platinum, but filtrates were caught in 
glass, and funnels and stirring rods made of glass were used. 
The silica not precipitated in the first and second evaporation was 
separated from the iron group and suitable corrections made. Cal- 
cium was invariably present in the magnesium precipitate and re- 
i Am. J. Sci., 44, 392 (1S92). - Tredwell, 2, 34S, New York (1906). 
