86 AGRICULTURAL ANALYSIS 



to five grams of ammonium chlorid are added and the mixture 

 heated upon the water bath until no further evaporation of am- 

 monia takes place. The mixture is washed in a 125 cubic centi- 

 meter flask and treated with a few drops of ammonia, boiled a 

 few minutes, cooled, filled to the mark, filtered through a small 

 dry filter and 100 cubic centimeters of the filtrate, corresponding 

 to 20 grains of the soil, used for the estimation of lime and 

 magnesium by the usual methods. 



Neubauer claims that the method described is recommended 

 particularly by reason of its speediness. According to him, it 

 also has other advantages. For instance, the precipitation by 

 ammonia and ammonium carbonate is avoided in which a slimy, 

 difficultly filterable precipitate is often produced which can easily 

 intertangle notable quantities of phosphoric acid and potash. The 

 filtrate from the iron and aluminium precipitate must, on account 

 of its ammonia and ammonium carbonate, be very carefully evap- 

 orated to dryness in order to avoid loss by spurting. 



Finally, one of the especial advantages of the process appears 

 to be that the disturbing influences of organic substances is com- 

 pletely eliminated and no impure potassium platinum chlorid or 

 brown colored phosphoric acid precipitate is any longer possible. 



This method, which is originally designed for application to 

 soils, may be used, apparently, with advantage in the examination 

 of slags containing small quantities of potash and phosphoric 

 acid to determine their value as fertilizing material. A quantity 

 of phosphoric acid and potash, especially the latter, which is 

 directly soluble in hydrochloric acid, may prove to be an index 

 of the comparative availability of these two plant foods contained 

 in slag. 



87. The Color of the Magnesium Pyrophosphate. After the final 

 ignition of the magnesium pyrophosphate, whether secured by 

 the citrate or the molybdate method, a black or grayish tint is 

 often noticed. This may be due to traces of organic matter 

 brought down by the precipitate and especially to a lack of care 

 in the initial ignition. Many devices have been proposed for 

 the purpose of avoiding this coloration, although general experi- 



