546 AGRICULTURAL ANALYSIS 



is brought together upon the filter the washing is finished by 

 means of boiling water. Sometimes the finely divided platinum 

 passes through the filter, which is easily detected by a gray metal- 

 lic tint which the filtered liquid assumes. In this case it is neces- 

 sary to allow it to settle for one or two days, decant the color- 

 less supernatant liquid and add the deposited matter to the filter 

 by means of cold water. Finally, the filter is dried and ignited 

 and there is obtained in this way the weight of metallic platinum 

 corresponding to that of potassium in the original sample, since 

 100 parts of platinum are equivalent to 47.57 of potash. 



466. Method of Potash Determination of the Union of Ger- 

 man Fertilizer Manufacturers. The method of potash deter- 

 mination employed by the Union of German Chemists is the same 

 as that recommended by the Potash Syndicate of Stassfurt, with 

 only slight modifications. 35 The German manufacturers, how- 

 ever, use the atomic weight of platinum, 194.8, instead of 197.2, as 

 employed by the syndicate. The factors, therefore, for conver- 

 sion in the two cases are slightly different. 



467. Methods Used at the Halle Station. (i) In Kainits and 

 other Mineral Salts of Potash. 30 Five grams of the prepared 

 sample are boiled for half an hour in a half liter flask with from 

 20 to 30 cubic centimeters of concentrated hydrochloric acid and 

 100 cubic centimeters of water, and afterwards as much water 

 added as is necessary to fill the flask about three-quarters full, 

 and the sulfuric acid is then precipitated with barium chlorid. To 

 avoid an excess of barium chlorid the solution used is of known 

 strength and is added first in such quantity as would precipitate 

 the sulfuric acid from a kainit of low sulfuric acid content. The 

 mixture is then boiled, allowed to settle and tried with a drop- 

 ping tube containing barium chlorid. If a further precipitate 

 appear, a few drops more of barium chlorid solution are added, 

 again boiled and allowed to settle. This is continued until barium 

 chlorid gives no precipitation. After the barium chlorid gives 

 no more precipitate a drop of dilute sulfuric acid is added to test 



M Methoden zur Untersuchung der Kunstdiingemittel, 1903 : 21. 

 34 Bieler undSchneidewind, Die agricultur-chemische Versuchsstation, 

 Halle a/S, 1892 : 76. 



