608 AGRICULTURAL ANALYSIS 



but the total volume of the filtrate and washings should not ex- 

 ceed 80 cubic centimeters. In this filtrate the phosphoric acid 

 may be determined by any one of the approved methods. 



515. Waste Leather. This material belongs probably to that 

 class of nitrogenous substances which has a small immediate value 

 for plant nutrition. The chief manurial value of the waste is 

 found in its nitrogenous content. The value of this for available 

 plant food has been investigated by Lindsey. 83 A complete resume 

 of the literature of the subject is also given by him. 



A good way of identifying leather waste is by the process pro- 

 posed by Dabney. 84 It depends on the color produced in a solu- 

 tion of iron phosphate by the tannin compounds derived from the 

 leather. The reagent is prepared by dissolving a freshly made 

 precipitate of iron phosphate from 10 grams of ferric chlorid in 

 400 cubic centimeters of an aqueous solution of 40 grams of 

 glacial phosphoric acid. A gentle heat promotes the solution of 

 the phosphate. 



In the case of a fertilizer supposed to contain leather, about one 

 gram of the material is treated with 30 cubic centimeters of water 

 and a few drops of sulfuric acid. The mixture is boiled and 

 poured on a filter. To a portion of the filtrate some of the solu- 

 tion of iron phosphate is added, and the mixture made alkaline 

 with ammonia. If leather be present in the sample, a purple or 

 wine color will be developed. Lindsey could easily detect the 

 leather when it was added in 10 per cent, quantities by the above 

 method, and he regards this method as superior to the micro- 

 scope, which is unreliable in the case of finely ground material. 



While leather, as such, decays slowly, and, therefore, is not at 

 once available for the nourishment of plants, it acquires greater 

 utility after digestion in sulfuric acid. Artificial digestion ex- 

 periments with leather previously treated with sulfuric acid show 

 that, approximately, 70 per cent, of the nitrogen pass into solu- 

 tion. Such 'a prepared leather has, therefore, an available co- 



85 Agricultural Science, 1894, 8 : 49, 98. 



Massachusetts Agricultural Experiment Station, Twelfth Annual 

 Report : 285. 



M North Carolina Agricultural Experiment Station, Bulletin 3. 



