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



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 1 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- 



> Am. J. Sci., 44, 392 (1892). ■ Tredwell, 2, 343, New York (1906). 



