388 AGRICULTURAL ANALYSIS 



the substance examined consists of seed of any kind, or residues 

 of seeds, such as oil-cake or anything else rich in alkaline phos- 

 phates, add a few cubic centimeters of a concentrated solution 

 of alum free from ammonia just before adding the cupric hy- 

 droxid, and mix well by stirring. This serves to decompose the 

 alkaline phosphates. If this be not done, cupric phosphate and 

 free alkali may be formed, and the protein-copper precipitate 

 may be partially dissolved in the alkaline liquid. 



Cupric Hydro.vid. Prepare the cupric hydroxid as follows: 

 Dissolve 100 grams of pure cupric sulfate in five liters of water, 

 and add 2.5 cubic centimeters of glycerol ; add a dilute solution 

 of sodium hydroxid until the liquid is alkaline ; filter, rub the 

 precipitate up with water containing five cubic centimeters of 

 glycerol per liter, and wash by decantation or filtration until the 

 washings are no longer alkaline. Rub the precipitate up again in 

 a mortar with water containing 10 per cent, of glycerol, thus 

 preparing a uniform gelatinous mass that can be measured out 

 with a pipette. Determine the quantity of cupric hydrate per 

 cubic centimeter of this mixture. 



Amid Nitrogen. The albuminoid nitrogen determined as above 

 subtracted from the total gives that part of the organic nitrogen 

 existing in the sample as amids and in other allied forms. 



339. Separation of Nitric and Ammoniacal from Organic Nitro- 

 gen. The nitrogen being present in three for/ns, viz., organic, 

 ammoniacal and nitric, the separation of the latter two may be ac- 

 complished by the following procedure : 3:! One gram of the fer- 

 tilizer is exhausted on a small filter with a two per cent, solu- 

 tion of tannin, using from 30 to 40 cubic centimeters in small 

 portions. This is sufficient to dissolve all the nitrates and the 

 greater portion of the ammoniacal salts, while the tannin ren- 

 ders insoluble all the organic nitrogenous compounds. The filter 

 and its contents are treated for nitrogen by the kjeldahl process. 

 When the distillation and titration are completed the solution 

 obtained by the aqueous tannin is added to the distilling flask 

 and the operation continued. This represents the ammoniacal 

 nitrogen. 



3S Aubin et Quenot, Bulletin de la Socit chimique de Paris, 1890, [3], 

 3 : 324- 



