EXAMINATION OF COMMERCIAL FERTILIZERS 129 



dish, wet down with 5 cc. of magnesium nitrate 

 solution (600 gms. per litre), dry, and ignite. 

 Ignition without addition of nitrate seldom in- 

 duces error, but is usually slower. After cooling, 

 treat with 5 to 10 cc. of hydrochloric acid, heat, 

 then transfer to a beaker; add about 30 cc. of 

 nitric acid, boil and filter. When the fertilizer 

 contains much iron and alumina more hydro- 

 chloric acid should be used. If made up with 

 phosphoric slags, gelatinous silica will appear, 

 which requires evaporation to dry ness, and 

 taking up with hydrochloric acid. 



A method recommended for fertilizers con- 

 taining very large quantities of organic matter, 

 consists in boiling with 20 to 30 cc. of concen- 

 trated sulphuric acid in a Kjeldahl flask, adding 

 crystals of sodium or potassium nitrate from time 

 to time until the organic matter is destroyed, 

 diluting and filtering. The presence of much 

 sulphuric or hydrochloric acid retards the sepa- 

 ration of the molybdate precipitate, and is best 

 avoided. Hydrochloric acid can be removed by 

 evaporating low with excess of nitric acid; sul- 

 phuric acid, however, cannot. 



In any case, dilute the clear solution to 200 

 cc., mix well, and take 50 cc. for the analysis 

 (representing 0.4 gm.) With phosphate rock, 

 half this amount will suffice. 



Add ammonia until it is just alkaline, then 

 acidify decidedly by addition of 5 cc. of nitric 

 acid; add 10 to 15 gms. of ammonium nitrate 



