592 AGRICULTURAL ANALYSIS 



may be omitted, and after cooling and adding a few drops of al- 

 coholic phenolphthalein solution the precipitation of the phos- 

 phate and other salts is accomplished in the same flask by means 

 of milk of lime, free of alkali, which is added until a strong red 

 colored saturated solution of calcium hydroxid is secured. Milk 

 of lime does not dissolve the barium sulfate and the filtrate con- 

 tains therefore no trace of sulfuric acid. After standing about 

 half an hour the potash is determined in an aliquot part of the 

 filtrate after acidifying with hydrochloric acid and a slight con- 

 centration thereof on the water bath with about five cubic cen- 

 timeters or more of 20 per cent, perchloric acid. 



Finally, special attention must be called to the fact that on 

 account of the very slight solubility of barium salts in alcohol 

 only a very small excess of the 10 per cent, chlorid of barium 

 solution should be used for the precipitation of the sulfuric 

 acid and only about two cubic centimeters of the five 

 per cent, hydrochloric acid should be used for the 

 solution of the ignited salts since with larger quantities of hy- 

 drochloric acid more milk of lime is necessary for saturation 

 and a large quantity of the lime salts will thus be incorporated 

 in the precipitate of the potassium perchlorate. 



496. Applicability of the Process. Experience has shown that 

 sulfuric acid is the only substance which need be removed from 

 ordinary fertilizers preparatory to the estimation of the potash 

 by means of perchloric acid. The fact that this process can be 

 used in the presence of phosphoric acid is a matter of great im- 

 portance in the estimation of potash in fertilizers, inasmuch as 

 these fertilizers nearly always contain that acid. The fact that 

 the French chemists noticed that magnesia was a disturbing ele- 

 rment in the process, as has been indicated in volume first, proba- 

 Ibly arose from its presence as sulfate. Neither Caspari nor 

 Kreider has noticed any disturbance in the results which can be 

 traced to the presence of magnesia as a base. 



If ammonia be present there is a tendency to the produc- 

 tion of ammonium perchlorate, which is somewhat insoluble in 

 the alcohol wash used. Solutions containing ammonia before 

 treating by the perchlorate method for potash should be ren- 



