POTASH METHODS 543 



directed under the lindo-gladding method, omitting in all cases 

 the addition of ammonia and ammonium oxalate. 



(3) Determination. Dilute 25 cubic centimeters of the solu- 

 tion made as directed under (2), (50 cubic centimeters, if less 

 than 10 per cent, of potassium oxid be present) to 150 cubic 

 -centimeters, heat to 100, and add, drop by drop, with constant 



stirring, a slight excess of barium chlorid solution. Without fil- 

 tering, add in the same manner barium hydrate in slight excess. 

 Filter while hot and wash until the precipitate is free from chlo- 

 rids. Add to the filtrate one cubic centimeter of strong ammo- 

 nium hydrate, and then a saturated solution of ammonium car- 

 bonate until the excess of barium is precipitated. Heat and add, 

 in fine powder, 0.5 gram of pure oxalic acid or 0.75 gram of 

 .ammonium oxalate. Filter and wash free from chlorids, evap- 

 orate the filtrate to dryness in a platinum dish, and ignite care- 

 fully over the free flame, below a red heat, until all volatile matter 

 is driven off. Digest the residue with hot water, filter through a 

 small fi'ter and dilute the filtrate, if necessary, so that for each 

 decigram of K 2 O there will be at least 20 cubic centimeters of a 

 liquid. Acidify with a few drops of hydrochloric acid and add 

 platinum solution in excess. Evaporate on a water bath to a 

 thick sirup and treat the residue with 80 per cent, alcohol (specif- 

 ic gravity 0.8645). Wash the precipitate thoroughly with 80 per 

 cent, alcohol both by decantation and after collecting on a gooch 

 or other form of filter. Dry for 30 minutes at 100 and weigh. 

 It is desirable, if there be an appearance of foreign matter in 

 the double salt, that it should be washed according to the previous 

 method with several portions of the ammonium chlorid solution 

 of 10 cubic centimeters each. 



(4) Factors. For the conversion of potassium platinochlorid 

 to KC1, use the factor 0.3071 ; to K 2 SO 4 , 0.3589, and to K 2 O, 

 0.1941. 



465. Potash Methods Recommended by the Official French Com- 

 mission. 33 By authority of law the President of the French 

 Republic appointed a commission for the purpose of prescribing 

 official methods of analyses of fertilizers. 84 This Commission was 



3 * La Sucrerie indigene et coloniale, 1897, 49 : 645: 50 : 45- 



34 Grandeau, Trait d' Analyse des Matieres agricoles, 3d Edition, 1897, 



