220 EXPERIMENT STATION RECORD. 



phosphoric acid must be removed before the precipitation of the lime 

 and magnesia, or the precipitates obtained as above must be purified 

 by reprecipitation, the filtrates being added to the principal solutions 

 of lime, magnesia, etc., respectively, and in this way absolute accuracy 

 approximated. This operation, however, is so troublesome, time con- 

 suming, and questionable in the hands of any except very skilled 

 analysts that where a number of ash analyses are to be made it becomes 

 wholly impracticable. In most cases the above method or a similar 

 one will sufiice, giving results approximately accurate and at all events 

 comparable with each other. 



Among those who have sought to remove the difiiculties due to 

 phosphoric acid, Konig^ attempted to separate it before the precipita- 

 tion of the lime and magnesia by combining it either with stannic 

 oxid, or with a ferric salt as iron phosphate. He gave the preference 

 to the latter, which is carried out as follows: Sufficient ferric chlorid 

 solution of known strength is added to the solution to unite with the 

 phosphoric acid as FePOi. The solution is made alkaline with soda 

 or ammonia, then slightly acid with acetic acid, some ammonium 

 acetate added, boiled and filtered. In the solution thus freed from 

 phosphoric acid, lime and magnesia may be estimated without diffi- 

 culty. Hornberger^ and Ulbricht'' have employed a similar method. 



The above method is not the one which Konig* describes in his 

 manual of agricultural analysis, but a simpler one similar to it. The 

 methods of analysis of the Association of Official Agricultural Chem- 

 ists adopted in 1898 (p. 78) prescribe the use of ferric chlorid. 



1 Landw. Vers. Stat., 10 (1868), p. 396. 



2 Ibid., 29 (1883), p. 281. 

 3 Ibid., 25 (1880), p. 401. 



* Die Untersuchung landwirthschaftlich und gewerblich wichtiger Stoffe. Berlin: 

 Parey, 1898, p. 189. 



[Concluded in next number.] 



