1895.] PUBLIC DOCUMENT — No. 33. 305 



the steamed or roasted leathers as regards its vahie. It is 

 to be noted, as before mentioned, that the dried blood was 

 nearly all digested by the action of the pepsin solution, and 

 may be regarded as a very excellent standard with which to 

 compare the various leathers. 



General Conclusions relative to Haw, Boasted or Steayned Leather. 



The results of the combined experiments in the field and 

 in pots, together with artificial digestion experiments, and 

 nitrification experiments, indicate that leather, either raw, 

 roasted or steamed, is a very slow-acting form of nitrogen as 

 a source of plant food. It certainly would be fraudulent to 

 sell it in mixed fertilizers as a source of organic nitrogen, and 

 the Massachusetts fertilizer law distinctly forbids it to be thus 

 utilized. Carefully conducted experiments by Wagner give 

 it a relative value of twenty, nitrate of soda being equal to 

 one hundred. From the mass of evidence at our command 

 it would seem that this figure about expresses its relative 

 worth as a direct source of plant food. If it is ofiered for 

 sale as a fertilizer, it should be sold as leather. AYhen nitro- 

 gen in organic matter has a value of sixteen to eighteen 

 cents per pound, nitrogen in raw, steamed or roasted leather 

 should be worth but three to six cents per pound. 



5. Action of Sulphuric Acid on Leather. 



Deherain and others suggest that if leather be dissolved in 

 sulphuric acid its nitrogen will be made as valuable as that 

 in any form of animal matter. No experiments, however, 

 are brought forward to prove such a statement, but it is 

 generally understood that many European manufacturers 

 thus turn leather waste to account. In order to study this 

 question more closely a number of experiments were carried 

 out by the writer, a few of which are presented below : — 



Experiment I. — Sixty-five grams of 50° B. sulphuric 

 acid were heated in a porcelain dish over a water bath of 

 about 90° C, and 12 grams of leather gradually added. A 

 dark, thick fluid resulted. Thirty cubic centimeters of water 

 were then added to dilute the thick fluid somewhat, and bone 

 ash was employed to dry ofl' the resulting semi-fluid mass. 



