1892.] PUBLIC DOCUMENT — No. 33. 277 



Methods of Fertilizer Analysis. 



Preparation of Sample. — The entire available sample is 

 spread upon a smooth, hard surface, and intimately mixed 

 without grinding, all lumps being broken up with a spatula. 

 Unnecessary loss or gain of moisture is to be avoided. 

 Moisture: dry 2 grams in the air-bath at 100 to 110° C. to 

 constant weight. 



1. Total Phosphoric Acid. — Weigh out 2 grams in a 

 platinum crucible, and destroy the organic matter by care- 

 fully burning in a muffle. Weigh when cool, to determine 

 the " organic and volatile matter." Digest the crucible and 

 contents with dilute hydrochloric acid, until the solution of 

 the latter is complete. Filter, and evaporate the filtrate to 

 complete dryness. The "insoluble matter" on the filter is 

 burned and weighed. The residue left from the evaporation 

 is taken up with dilute nitric acid, if the molybdic method is 

 to be followed, but with hydrochloric acid if method (2) is 

 preferred. The solution after filtering is made up to a vol- 

 ume of 200 cubic centimetres with distilled water. 



(1) The molybdic method : 25 cubic centimetres of the 

 solution are digested in a water-bath at 65° C. from one to 

 two hours, with an excess of molybdic solution. The pre- 

 cipitate is brought upon a filter, and washed with water 

 containing a little molybdic solution. It is then dissolved in 

 ammonia water, the solution nearly neutralized with hydro- 

 chloric acid, and magnesia mixture added slowly, with con- 

 stant stirring. The precipitate is allowed to stand at least 

 three hours, when it is filtered through a Gooch crucible, 

 washed with dilute ammonia, ignited and weighed. 



(2) The following method is occasionally employed when 

 phosphates of iron and alumina are present in small quanti- 

 ties only : To 50 cubic centimetres of the hydrochloric acid 

 solution add ammonia in slight excess. After standing a 

 few minutes, acidify with acetic acid, and filter off the phos- 

 phates of iron and alumina, washing carefully with water. 

 To the filtrate add sufficient oxalate of ammonia to precipi- 

 tate all the lime ; digest for several hours at a temperature 

 below boiling, and filter through double filters which have 

 previously been washed with oxalate of ammonia, washing 



