ON THE EXAMINATION OF SOILS 145 



wash with diluted ammonia water (1 part am- 

 monia to 8 parts water) until filtrate gives no 

 coloration with nitric acid and silver nitrate. 

 Dry thoroughly, remove precipitate to tared 

 porcelain crucible, burn filter-paper and add the 

 ash to the crucible and its contents, and ignite, 

 at first slowly, then to intense heat; cool, and 

 weigh as Mg2P2O?. 



Alkalies. To the last filtrate add ammonia, 

 boil to expel excess of ammonia, filter and wash. 

 Evaporate the filtrate to dryness, heat below 

 redness to expel ammonia salts, add 30 cc. of 

 water, then a few drops of barium hydroxide so- 

 lution, and heat to boiling. Filter and wash 

 with hot water. To the filtrate add ammonia 

 hydroxide and ammonium carbonate, filter, and 

 wash with hot water. Evaporate to dryness and 

 determine potassium by adding platinic chloride 

 to slight excess, and evaporate almost to dry- 

 ness on water-bath; then add 40 cc. of 80 per 

 cent alcohol, and allow to stand for one hour; 

 then decant on weighed filter and add fresh 

 alcohol, and repeat two or three times, and then 

 transfer to filter and wash with ether; dry, cool 

 in desiccator, and weigh. From total weight 

 deduct weight of filter-paper, or a Gooch crucible 

 with asbestos filter may be used. Precipitate 

 is potassium platinic chloride. In place of alcohol 

 a mixture of alcohol and ether is preferable in 

 proportion of 2 and 1. 



Sodium. The mixed alkalies are weighed as 



