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 LIBRARY 
 
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 AGRICULTURAL 
 
 COLLEGE 
 
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 DATE DUE 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 UNIYERSITY OF MASSACHUSETTS 
 LIBRARY 
 
 CAkD 
 
LEATHER REFUSE; 
 
 Its Value in Agriculture. 
 
 
 BY 
 
 J. B. LINDSEYy Ph. D., 
 
 MASSACHUSETTS STATE EXPERIMENT STATION, 
 AMHERST. 
 
 W. F. HCMPHRSY, 
 GENBVA, N. V. 
 1894. 
 
L L f 
 
Agricultural Science. 
 
 Vol. VIII. FEBRUARY, 1894. No. 2. 
 
 LEATHER REFUSE — ITS VALUE IN AGRICUL- 
 TURE. 
 
 BY J. B. LINDSEY. 
 First Paper. 
 
 During the past few years, claims have been made at various 
 times that large quantities of leather shavings and the like have 
 found their way into the so-called commercial fertilizers that are 
 so widely used by the farmers of the United States. The writer 
 has no means of knowing whether this claim is true or not. It 
 should be the object of the fertilizer manufacturer to utilize all 
 kinds of waste products that possess distinct manurial value. 
 By so doing he not only benefits himself, but the farmer as well. 
 
 It was very early assumed from its chemical character, without 
 any exact experiments upon which to base the assumption, that 
 leather refuse would yield its nitrogen as plant food very slowly 
 if at all. 
 
 Methods Employed to Make the Nitrogen Available to 
 Growing Plants. 
 
 The first method suggested, so far as the writer has been able 
 to ascertain, was that prescribed by F. O. Ward*, of England, in 
 1857, for turning to account woolen rags, wool, silk and leather 
 clippings. The process as described was as follows : The refuse 
 was introduced into an ordinary autoclave digester, and there 
 kept for about three hours, surrounded by steam heated to a pres- 
 sure of from three to five atmospheres. Wool required a higher 
 temperature than leather, and silk than wool. The materials 
 condensed a portion of the steam, and absorbed its heat. This joint 
 action converted the animal matter into a friable substance, which, 
 
 * Report by the Jtiries of the International Exhibition, 1862. Reporter, A. 
 W. Hoffman. Repertory of Patent Inventions, Aug. 1857, page 137. 
 
50 AGRICUI.TURAI, SCIENCE. Vol. VIII. No. 2. 
 
 however, still retained its original form and aspect. It was then 
 ground fine, sifted, and bagged. " The details of the process, the 
 fuel- and labor-saving arrangements that have been learned, point 
 by point, by costly manufacturing experience cannot, ' ' says Ward, 
 ' ' with propriety be divulged, ' ' The final product is described as a 
 dark colored powder. The nitrogen in the finished product is 
 said to exist to a small extent, as ready formed ammonia, being 
 in combination with ulmic and humic acids developed during the 
 process. It was stated at the time, that this manufacturing 
 process was carried on at large works on the Thames. The ma- 
 terial for the most part was sold to manure manufacturers, who 
 used it as an ingredient of their several fertilizing compounds, 
 and it was ' ' used by many farmers who are not aware of the fact. ' ' 
 Ward says that ' ' while this material is not as active as some 
 other forms of organic nitrogen, it possessed distinct value as a 
 fertilizer."* 
 
 Kdw. Toynbect in 1858, also described a process whereby 
 leather and wool waste could be cooked in sulfuric acid, and be 
 made more available as a fertilizer. He said " that to one cent- 
 ner of sulfuric acid, four or five centners of wool or leather waste 
 could be added." The writer does not see how such a large 
 amount of leather could be added to the acid, as will be shown 
 further on. L,. MeyerJ speaks of dissolving all such refuse sub- 
 stances in warm sulfuric acid, and neutralizing the moist mass 
 with bone. 
 
 A Lipowitz§ notes the fact that the Posner fertilizer factory 
 utilizes all such kinds of waste, as have already been referred to. 
 
 Runge^ speaks of rendering leather and wool more available, 
 by dissolving them in a mixture of Glauber's salt and quicklime. 
 This chemist manufactured a fertilizer upon a large scale from 
 these materials. 
 
 R eichardt*Mescribes his method of subjecting the leather refuse 
 
 * The writer does not know whether this process is still in operation in 
 England, for utilizing the leather, wool, and silk wastes. 
 
 t Repertory of Patent Inventions 1858, p. 389 ; Jahresbericht Agric. 
 Chem., 1859. 
 
 t Jahresbericht Agric. Chem., 1859, 228. 
 
 I Allgem. Zeitung fiir deutsche Land, und Forstwirthe, 1859, 153. 
 
 ^Jahresbericht Agric. Chem., 1865. 
 
 ** Zeitschrift fiir deutsche Landwirtschaft, 1865, 136. Jahresbericht Agric 
 Chem., 1865. 
 
l894- AGRICUI^TURAL SCIENCE. 5 1 
 
 to steam pressure, and then drying it quickly. After such a 
 treatment he found 15.75 per cent, of the material to be soluble in 
 boiling water, and that after standing for some time, 20 per cent, 
 could be dissolved. By treating the dry leather that had been sub- 
 jected to steam, with 20 to 40 per cent, sulfuric acid, he was ena- 
 bled to dissolve from 22 to 29 per cent, of the leather in water. 
 With a 5 per cent, solution of crystallized soda, 28.8 per cent, 
 could be brought into solution. He therefore concluded that 
 the best method was to subject the leather to the action of a 
 weak soda solution. 
 
 Coignet's* method was reported in 1874 by H. Mangon. 
 Briefly stated, it is as follows : The refuse material is placed in 
 a room having a cubic area of 20 meters. Directly outside of the 
 room is a coke oven, connected with a chimney that has an open- 
 ing into the room containing the material to be treated. Into 
 this chimney are conducted jets of steam, so that the room is 
 heated from 150° to 160° C. for several hours by this moist chim- 
 ney air. Under these conditions the leather swells somewhat, 
 and becomes dark, brittle, and can easily be rubbed to a powder. 
 
 Storerf says, "It is evidently with reference to this process, 
 that the statement has recently been made, that certain manufac- 
 turers of fertilizers at Paris devote themselves particularly to the 
 preparation of torrefied wool, horn, leather, and even bone, the 
 leather having first been steamed strongly to remove oil and gela- 
 tine." 
 
 I^'Hotet describes a method whereby such waste material as 
 wool, leather, etc., can be converted into sulfate of ammonia. 
 He suggests dissolving the material in a ten per cent, solution of 
 caustic soda in the cold. The substances will be partly dissolved, 
 or their structure more or less destroyed. The jelly-like mass is 
 then mixed with caustic lime till it becomes of a doughy consis- 
 tency. It is then brought into iron retorts, and heated at first at 
 as low a temperature as possible in order to prevent the dissocia- 
 tion of the ammonia, which is caught in sulfuric acid. After the 
 gas has been nearly driven off, the retorts are subjected to red 
 
 * Organ der Verein f. Riibenz. Industrie in CEster-Ungarn, 1874, 32. 
 Jahresbericht Agric. Chem. 1873-1874, 37. 
 
 ^ Agriculture 1., 382. 
 
 X Centralblatt fiir Agric. Chem. 5, 258. lUustrirte landw. Zeitung, 1874, 
 No. 2. 18. 
 
52 AgricuIvTurai, Science. Vol. viii. No. 2. 
 
 heat. At the end of the operation, a white powdery substance is 
 left behind, consisting of carbonate of soda and caustic lime. 
 By cooking this substance with water, caustic soda is formed and 
 can be again utilized. By this method all the nitrogen is obtained. 
 The resulting sulfate of ammonia is somewhat colored. 
 
 For utilizing leather Riimpler* suggests the following method : 
 In lead or iron jacketed kettles, sulfuric acid of 50° B. is heated 
 very hot, and leather stirred in till a dark brown fluid is obtained. 
 This fluid is then used to dissolve the phosphate of lime. He re- 
 marks that ' ' the nitrogen is saved, and without doubt is much 
 more available from the fact that the tannin is destroyed." 
 
 Brhardt t suggests that such refuse material be slowly burned 
 in closed ovens, and the gas collected in moist muck, till the lat- 
 ter becomes saturated. This muck mixed with superphosphate 
 gave, he says, a quick acting manure. 
 
 DeherainJ says that this leather refuse can be dissolved in sul- 
 furic acid, and the excess of acid neutralized with phosphate of 
 lime. In this way he claims a very active fertilizer can be ob- 
 tained at a low cost. 
 
 The writer understands that this latter method has been in quite 
 general use for many years by European manufacturers. Not 
 only has leather been thus treated, but also a great variety of 
 nitrogen-containing refuse materials. American manufacturers 
 also subject various waste materials to the action of sulfuric acid, 
 in order to render them more quickly available. 
 
 From the many methods suggested for the utilization of leather 
 waste, it is evident that, in the older countries, especially Eng- 
 land, France and Germany, this material after having been sub- 
 mitted to some mode of treatment, is quite generally used, to a 
 greater or less degree, in the manufacture of commercial fertilizers. 
 
 Petermann § says, ' ' that it is well-known that certain Belgian 
 and French manufacturers use leather in their products, but that 
 such goods contain, in addition, nitrogen in other forms, such as 
 blood, horn meal, sulfate of ammonia and nitrate of soda." 
 He further states that the "factories producing this material are 
 numerous, and a considerable q uantity is produced annually." 
 
 *Kaufliche Diingestoffe. H. Riimpler, 1875 (Thaer Bibliothek). 
 
 t Jahresbericht Agric. Chem., 1880, 337. 
 
 tDeherain, Chimie Agricole, [1892], 624. 
 
 I Recherches de Chimie et Physiologic [1886], 144. 
 
i894- Agricultural Scienck. 53 
 
 Manurial Value of Prepared Leather Waste. 
 
 The different experiments made to prove the value of leather 
 have been conducted either with untreated finely ground leather, 
 with torrefied leather, or with leather steamed under pressure. 
 
 Three different methods have been used, in testing the agri- 
 cultural value of leather: (a) by directly testing its fertilizing effect 
 either in pot or plat experiments ; (b) by artificially digesting it 
 with a pepsin solution ; (c) by noting the length of time required 
 to nitrify it. The first method is by far the most interesting, and 
 leads to direct results. The other two serve at least to confirm 
 the results obtained by the first method. 
 
 (a) Pot and Plat Experiments. 
 
 Very early experiments are not to be found in the literature. 
 
 The first experiment recorded was made by Ladureau,* and 
 lasted but a single season. He found that 2500 kilos, of torrefied 
 leather yielded 30,100 kilos, of sugar beets, testing 8.83 per cent, 
 of sugar, and 2500 kilos, of the same leather plus 200 hectolitres 
 of lime gave 38,600 kilos, of beets, with 10. 10 per cent, sugar. 
 The same area of land without leather, yielded 20,000 kilos, of 
 sugar beets testing 10.93 percent, sugar. Petermann remarks on 
 these results as follows : " In spite of the increased yield obtained 
 by using the leather, the experiment was not a success financially 
 and further, the beets produced with the aid of the leather were 
 poorer in quality than those without it." 
 
 In 1880, Petermann t carried out a series of experiments with 
 ground, steamed leather, to test its manurial value. It was 
 very dry and brittle, and contained 7.51 per cent, of nitrogen and 
 0.81 per cent, of phosphoric anhydride soluble in hydrochloric 
 acid. 
 
 The experiments were carried on in the plant house in pots, 
 with oats ; in the garden, with the horse bean {Vidafaba) ; and 
 in the field, with sugar beets, 
 
 /. Experiments with Oats in Pots. 
 
 Kach test was made in duplicate. The soil was what might be 
 called a sandy clay, each pot holding 4,000 grammes. The ferti- 
 lizer was mixed with three-fourths of the soil of each pot. To the soil 
 
 * Annales Agron., 1878 ; Loc. cit., 146. 
 
 t Loc. cit., 144, Centralbl. Agrie. Chem. 10, 590. 
 
54 Agricultural Science Vol. viii. No. 2. 
 
 ineacli pot were added 0,25 gramme of nitrogen, 0.30 gramme of 
 phosphoric acid, and 0.20 gramme of potash. 
 
 Resui,ts — Average oe the Duplicates, Expressed in Grammes. 
 
 Entire plant. Straw. ChaflF. Grain. 
 Unmanured 22.34 15.19 0.95 6.20 
 
 Series i. 
 Nitrogen 
 
 (a) Leather 34.85 26.65 1.25 6.95 
 
 (b) Dried blood 5i-9i 36.68 1.82 13.41 
 
 Series ii. 
 Nitrogen + Phosphoric Acid. 
 
 (a) Zi?a/A(?r + precipitated phosphate.. 39. 93 31.28 1.15 7.50 
 
 (b) Blood + precipitated phosphate 51.97 36.45 1.91 13.61 
 
 Series hi. 
 
 Nitrogen + Phosphoric Acid + Potash. 
 
 (a) Leather + precipitated phosphate 
 
 + muriate of potash A30.55 21.90 1.09 7.56 
 
 (b) Dried Iblood + precipitated phos- 
 phate + muriate of potash 37.40 29.65 1.82 15.93 
 
 In observing the results of the experiments, we notice especially 
 with reference to the grain produced, that the leather did not 
 increase the yield to any appreciable extent over that of the 
 unfertilized pots. When phosphoric acid and potash were applied 
 with the leather, a slight increase in the yield of grain was noticed, 
 while in case of the dried blood plus the phosphoric acid and pot- 
 ash, the yield was twice that of the unfertilized pot. 
 
 (b) Garden Experiments with Horsebeans. 
 
 The soil was the same as in the previous experiment, Size of 
 
 plats, 60 sq. meters. The fertilizer applied was leather and 
 
 nitrate of soda. Nitrogen was applied at the rate of 58.5 lbs. per 
 
 acre. 
 
 Results per Plat. 
 
 stems and pods Beans in Beans per acre 
 in kilos. kilos. in kilos. 
 
 Unmanured 9,869 1,131 37.7oo 
 
 Leather 12,822 1,178 39.268 
 
 Nitrate of soda 11,465 2,035 67,832 
 
 It will be observed that the leather produced only a slight 
 increase in the yield of beans. 
 
1 894- Agricultural Science. 55 
 
 (c) Field Experiments with Sugar-beets. 
 Same soil as in previous experiments. Kach plat measured i 
 ar. The fertilizer was applied at the rate of 42^ pounds of 
 nitrogen, and 528 pounds of phosphoric acid per acre. 
 Resui,ts per Hectare. 
 
 Percentage 
 Kilos. increase over 
 
 unmanured. 
 
 Unmanured 34)830 
 
 Soluble phos. acid 34.38o —1.5 
 
 Water and citrate sol. phos. acid 34,290 — 1.2 
 
 Citrate sol. phos. acid 34,38o — 1.5 
 
 Unmanured 33,840 
 
 Leather + sol. phos. acid 37,890 ' 11. 9 
 
 Leather -\- water sol. + citrate sol. phos. acid 37, 180 10.7 
 
 Leather-!- citrate sol. phos. acid 35,9^0 6.0 
 
 Unmanured 32,940 
 
 Nitrate of soda -f- sol. phos. acid 43,38o 28.1 
 
 Nitrate of soda + water -|- citrate sol. phos. acid 42,070 24.2 
 
 Nitrate of soda -f- citrate sol. phos. acid 43,830 29.4 
 
 While the leather has shown its effect, it runs far behind the 
 nitrate of soda. Petermann says that from a financial standpoint 
 the leather shows a loss and the nitrate of soda a gain. Of his 
 results the experimenter makes the following resume : 
 
 " With horsebean, the leather shows practically no influence 
 the first year. With oats and sugar beets an increase is noted, 
 but this is slight when compared with that from blood and nitrate 
 of soda." In a later publication, Petermann says that in his 
 experiments from 1 880-1 885, the various forms of nitrogen have 
 shown the following relative worth : i . Nitrate of soda ; 2. blood; 
 3. dissolved wool ; 4. ground bone ; 5. raw wool ; 6. leather. 
 
 Deherain* gives the results of the following experiments con- 
 ducted in the field at Grignon with ground leather. The results 
 with wheat in 1880 and 1881, show the residual effect of that 
 applied to potatoes in 1879 : 
 
 Potatoes. Wheat. 
 
 Hectolitres. Grain, Straw. Grain. Straw. 
 
 Qtm.* Otm. Qtm. Qtm. 
 
 Unfertilized.-. 224 25.0 37.25 164 20.5 
 
 Leather, 2000 kilos 295 27.5 40,00 23.4 38.7 
 
 Leather, 1000 kilos 277 25,0 38.00 23 37.6 
 
 * Qtm. = quintal metrique = 100 kilograms. 
 
 Deherain remarks that his experiments make it clear that the 
 
 * Chimie A^ricole ( 1892), 619. 
 
(Dry Matter). 
 
 1889. 
 
 Average of 
 
 Kilos. 
 
 both years. 
 
 47 
 
 190 
 
 48 
 
 178 
 
 52 
 
 175 
 
 61 
 
 152 
 
 43 
 
 102 
 
 56 Agriculturai< Science. voi. viii. No. 2. 
 
 leather yields its nitrogen very slowly. He does not state whether 
 the leather used had been steamed, roasted, or was untreated. 
 
 Miintz* and Girard, in connection with their experiments on 
 the nitrification of various nitrogen-containing organic sub- 
 stances, carried out also a series of field experiments with various 
 nitrogenous materials. Each plat had an area of one ar. and 
 received 1.25 kilos of nitrogen the first year, together with the 
 necessary quantity of phosphoric acid and potash. No manure 
 was applied the second year. The soil was light and sandy, 
 being quite favorable to nitrification. The plats were planted 
 with fodder com during both years. 
 
 Fodder Corn Grown Upon One Ar. 
 
 1888. 
 
 Form of nitrogen. Kilos. 
 
 Nitrate of soda 143 
 
 Dried blood 130 
 
 Roasted horn 123 
 
 Roasted leather 91 
 
 No nitrogen 59 
 
 The above results show that leather even when roasted is quite 
 inferior in its action to dried blood and nitrate of soda. 
 
 Marckerf gives the following results obtained by Seyffert, at 
 Halle, with cole-rape : 
 
 Form of nitrogen. Yield in grammes. 
 
 No nitrogen 75.5 
 
 riveather 469 
 
 ,, .. Steamed bone meal 1,572 
 
 No nitrogen j ^^^^^ ^;g^^ 
 
 [^Nitrate soda 2,607.5 
 
 In order to control the above experiment another test was car- 
 ried out with oats by Julius Albert-Miinchenhof. 
 
 YlEl<D. 
 
 Form of nitrogen. Grain. Straw. Roots. Total. 
 
 Grammes. Grammes. Grammes. Grammes 
 
 No nitrogen 5.2 15.7 14.3 38.2 
 
 Nitrate of soda 48.9 62.6 27.9 139-4 
 
 Dried blood 24.8 44.5 18.5 87.8 
 
 Iveather 13.3 22.2 13.6 49.1 
 
 " fermented 21.5 36.4 17.2 75.1 
 
 Marcker remarks that leather produced but a slight increase 
 over the unfertilized, and that the quality of the grain was poor- 
 est when not any nitrogen was used, or when leather was applied. 
 
 *Ann. Agron., 17, 289-304; Biedermann's Centralblatt, 20, 656. 
 tjahresbericht Agr. Chemie, 1883, 241. 
 
Average 
 
 Average 
 
 and 2d year. 
 
 three years. 
 
 lOO 
 
 100 
 
 67 
 
 69 
 
 59 
 
 64 
 
 53 
 
 61 
 
 12 
 
 20 
 
 1894. Agricultural Science. 57 
 
 Wagner* has made an exhaustive study of the value of diflfer- 
 ent forms of nitrogen, having conducted 366 plat and pot experi- 
 ments. The experiments were carried on for several successive 
 years in a soil rich enough in lime to favor nitrification, and 
 every effort was made to have the conditions equal in all cases. 
 But a very brief resume can be given at this time. One experi- 
 ment was conducted for three successive years upon small plots 
 of soil. Summer rye was planted the first year, summer wheat 
 the second, and carrots the third year. Placing the value of the 
 returns from the nitrate of soda plats at 100, the other forms of 
 nitrogen had the following relative worth : 
 
 I St year. 
 
 Nitrate of soda 100 
 
 Blood 67 
 
 Fish 51 
 
 Steatned bone meal 42 
 
 Leather 13 
 
 Experiments were also conducted in pots with various soils, 
 but the results cannot be noticed here. 
 
 In concluding his remarks relative to this subject Wagner 
 says, "When I take all things into consideration 
 I think I may present the following figures, as an expression of 
 the relative value of nitrogen in different forms of nitrogen-con- 
 taining material : 
 
 Nitrate of soda lOO 
 
 Sulfate of ammonia 90 
 
 Blood, horn meal and green crops 70 
 
 Fine ground bone, fish and tankage 60 
 
 Stable manure 45 
 
 Wool dust 30 
 
 Leather 20 
 
 So far as the writer has been able to ascertain, Wagner does 
 not state the form of the leather used. 
 
 Taking the price of nitrogen in nitrate of soda at 14.8 cents, a 
 pound of nitrogen in stable manure would be worth 6.7 cents, 
 and in leather 2.8 cents. 
 
 Note by the Editor : From this resume of direct tests of the fertilizer 
 value of leather, the experiments of F. H. Storer {Bulletin of the Bussey 
 Institution, 2, 58-71) should not fail of mention. He tested the manurial 
 effect of sheep-skin and sole-leather, raw and roasted, on several soils in 
 pots, applying various phosphatic and potassic salts in solution. The crop 
 
 * Die Stickstoffdungung der Landw. Kulturpflanzen, p. 242. 
 
58 Agriculturai. Science. voi. viii. No. 2. 
 
 used was buckwheat. The results were as follows (expressed in weight of 
 total crop in grammes) : 
 
 with phos- 
 phate of 
 With With With potash and 
 
 rain- sulfate phosphate nitrate of 
 
 water. of potash. of potash. lime. 
 
 No leather used : 
 
 In Berkshire sand. 0.200 0.200 0.155 0.665* 
 
 In Provincetown sand 0,170 0.165 3.050 
 
 In loam and sand 0.270 0.160 5-830 
 
 Raw sheep-skin (20) : 
 
 In Berkshire sand (1300).... o.ioo 0.130 0.055 0.640* 
 
 In Provincetown sand (1450) 0.080 o. ico 1.400 
 
 In loam and sand (1320) 0.170 0.120 4.020 
 
 Raw sole leather (40) : 
 
 In Berkshire sand (1300).... o.iio 0.115 0.120 0.280 
 
 In Provincetown sand (1450) 0.120 o.iio 2.820 
 
 In loam and sand (1320) 0.130 0.150 3.720 
 
 Roasted sheep-skin (20) : 
 
 In Berkshire sand (1300) ... 0.105 0.190 0.060 0.250 
 
 In Provincetown sand (1450) 0.250* 0470* 0.345* 
 
 In loam and sand (1320) 0.850 0.700 3.060 
 
 Roasted sole-leather (40) : 
 
 In Berkshire sand (1300).... 0.220* 0.23Q 0.210* 0.360* 
 
 In Provincetown sand (1450) 0.910 i-750 3.120 
 
 In loam and sand (1320) 2.120 1.980 4.785 
 
 * Immature when harvested. 
 
 Storer says: "It will be seen plainly enough, that while neither the 
 sheep-skin nor the sole-leather supplied any nitrogenous food to the buck- 
 wheat plants, some nitrogen was unquestionably obtained by the plants 
 from the roasted leathers ; a little from the roasted sheep-skin and a deci- 
 dedly larger amount from the roasted sole-leather. ... In all cases, 
 the light bulky material tended to interfere with the growth of the plants. 
 The roast-leather jars exhibited a marked growth of fungus, the raw leather 
 jars showed none, corroborating the evidence as to the existence of available 
 products in the roast leather. There is but little in the results above given 
 to encourage the belief that roasted leather can have any definite money 
 value as a manure." 
 
 (b) Artificial Digestion Experiments with Leather. 
 Stutzer and Klinkenberg^ were the first to propose this method. 
 They argued that the amount of nitrogenous material that 
 could be dissolved or digested would give a fairly correct idea of 
 the value of the substance as a source of nitrogen for growing 
 plants. They prepared the digestive fluid by extracting the 
 inner lining of a pig's stomach, cut fiue, with 5 litres of 0.2 per • 
 cent, hydrochloric acid for two days, filtering the solution, and 
 preserving in glass stoppered bottles, adding a few grammes of sal- 
 
 *Joiurnal fiir Landw., 1882, p. 365. Konig's Vntersuchung Landw. und 
 Gewerblich. Wichtiger Sioffe, p. 219. 
 
i894- AgriCULTURAI. SCIENCE. 59 
 
 icylic acid to prevent fermentation. They submitted a variety of 
 materials to the action of this solution. A few results are given 
 below: 
 
 Per cent, of nitro- 
 Substance. gen digested. 
 
 Blood 89.75 
 
 Leather (cooked, and then roasted) 39-19 
 
 Raw bone 98.70 
 
 Steamed bone 90.50 
 
 Drs. Shepard and Chazal* afterwards submitted a great variety 
 of nitrogen-containing materials to the action of Stutzer's solu- 
 tion. Several of the results obtained are presented below. 
 
 Per cent, of nitro- 
 gen digested. 
 
 Roasted leather meal* 37-8o 
 
 Dried blood (black) 78.61 
 
 Fish scrap 88.67 
 
 * The author's remark that "this prepared leather was an excellent article, so far as 
 preparation goes, and one capable of being used in the fertilizer trade, without much fear of 
 detection." 
 
 Johnson, Farrington and Wintonf, instead of using Stutzer's 
 solution, dissolved 5 grammes of Golden Scale Pepsin in 1000 c.c. 
 of 0.2 per cent, hydrochloric acid and digested a variety of sub- 
 stances in this fluid. Their investigation is the most valuable we 
 possess in this direction. A few of their results may be cited. 
 
 Per cent, of nitro- 
 gen digested. 
 
 Dried blood (two samples) - 97.30 
 
 Dry ground fish 71.20 
 
 Leather No. ?,* , 23.40 
 
 Leather treated by benzine process 35-90 
 
 Leather treated by superheated steam 33-30 
 
 Mixed fertilizer A containing 2.02 per cent, leather 
 
 nitrogen 23.40 
 
 Mixed fertilizer B containing 200 per cent, leather ni- 
 trogen and 1.75 per cent, blood nitrogen 55- 60 
 
 * Fine and brittle, but method of preparation not known. 
 
 In this connection it might be in place to mention the experi- 
 ments recorded on the putrefaction of ammoniates, at first suggested 
 by A. Morgen. J He put leather and horn meal in water to which 
 a small amount of fecal extract had been added, and then allowed 
 the solution to .stand for 31 days at 30° C. The nitrogen made 
 solution was then estimated. 
 
 *See Report of Conn. Experiment Sta., 1885, p. 117. 
 
 ■f Loc. cit. 
 
 X Landw. Vers. Stat., 1880, 50 ; Biedermann's Centralblatt, 9, 801. 
 
6o Agricultural Science. Voi. viii. No. 2. 
 
 In experiment I=io grammes material -|- looo cc.m. water were used. 
 
 In experiment 11=5 grammes material + looo cc.m. water + 5 cc.m. fecal 
 
 extract. 
 In experiment III, the same with 10 grammes material + 5 cc.m. fecal 
 
 extract. 
 
 Per cent, of 
 soluble nitrogen . 
 
 Leather meal, average of 3 experiments 34-56 
 
 Horn meal, average of 3 experiments 61.62 
 
 Johnson* repeated Morgen's work on a very large number of 
 
 substances ; a few of the results are given below. He allowed 
 
 his solution to stand two weeks. 
 
 Per cent, nitrogen 
 soluble. 
 
 Blood 76.80 
 
 Fish 78.10 
 
 Fish 54.60 
 
 Bone 79.00 
 
 Leather, No. 3 12.20 
 
 Steamed leather 42.30 
 
 * ' Prepared ammoniate ' ' (probably leather) 35-70 
 
 Johnson remarks that "this test of putrefaction draws the same 
 
 line between those classes of ammoniates that was drawn by the 
 
 pepsin digestion." 
 
 (c) Nitrification Experiments with Leather. 
 
 These experiments were carried out by Miintz and Girardf 
 with quite a number of nitrogen-containing substances. They 
 were conducted in the laboratory, and care was taken to see that 
 the soil was properly aired, and that moisture, temperature, etc. , 
 were favorable to the experiment. Ordinary soil was at first used, 
 the amount of nitrates present being carefully noted and a small 
 amount of the substances to be nitrified then added. After a 
 certain time, the nitrates were washed out with water and esti- 
 mated. A very short resume is here presented : 
 Nitrogen Nitrified, per 100 Parts of Nitrogen Added to the 
 
 Soil. 
 
 I. II. III. 
 
 30 days. 39 days. 32 days. 
 
 Sulfate of ammonia 75 83.76 83,76 
 
 Dried blood 72.44 73-56 84.50 
 
 Roasted horn 71.03 73-17 46.82 
 
 Roasted leather 11.62 16.47 13.26 
 
 In order to study the influence of different kinds of soil upon 
 
 the process of nitrification, the experiment was repeated with soils 
 
 from various sections of the country. 
 
 * Loc cit. 
 
 fAnn. Agron. 17, 290; Agric. Science, 7, 408-12; Deherain, Chimie 
 Agricole. p. 621. 
 
i894. Agricultural Science. 6i 
 
 Nitric Nitrogen Found in Different Soiw Within a Certain Time, 
 
 Marsh soil, 
 
 Light soil Chalky Garden Very heavy sour, 
 
 of Joinville. soil. earth. limey clay. Bretagne. 
 
 Grammes. Gram.m.es. Grammes. Grammes. Grammes. 
 
 Sulfate of ammonia... 2.69 1.78 0.51 None 
 
 Blood 1.62 .73 .036 " 
 
 Roasted horn 1.22 1.08 .029 " 
 
 Roasted leather 0.41 0.24 0.55 .036 " 
 
 These experiments in general coincide with field and pot ex- 
 periments as well as with artificial digestion experiments. It is 
 worthy of note, that the light sandy soil was most favorable to 
 the process of nitrification, while the very heavy clay, and espe- 
 cially the sour marshy soil was decidedly unfavorable to the action 
 of nitrifying organisms. 
 
98 AgricuIvTurai, Scie;nce. Vol. VIII. No. 3. 
 
 .^ 
 
 LEATHER REFUSE— ITS VALUE IN AGRICUL- 
 TURE. 
 
 BY J. B. LINDSEY. 
 
 Second Paper. 
 
 Notes on Work Done with Leather at the Massachusetts 
 
 State Experiment Station. 
 
 It is desired at this time to refer briefly to some tests carried 
 
 out by the writer at the above station. 
 
 Can leather be identified in fertilizer mixtures f 
 
 If one were to depend upon the microscope, it would certainly 
 
 be an impossibility to recognize leather in finely ground fertilizer 
 
i894- AgrICULTURAI, SCIENCE. ' 99 
 
 mixtures. Even if material of a fibrous structure were detected, 
 it would be nothing strange, for all flesh presents such a struc- 
 ture. After leather has been submitted to heat or pressure, all 
 structure is destroyed. Able microscopists who have attempted 
 to identify the leather under the microscope, report it an impossi- 
 bility. 
 
 With chemical reagents, one is more successful. At least, tan- 
 nic or gallic acids, from their well known reaction with an iron 
 salt, are easily recognized, and while one perhaps could not posi- 
 tively declare that the tannic or gallic acids present were derived 
 from leather, it certainly would be highly probable. 
 
 Dr. C. W. Dabney,* when director of the North Carolina Ex- 
 periment Station, published a bulletin in which he suggests that 
 the best reagent for recognizing the tannic acid, is a phosporic 
 acid solution of phosphate of iron. He states that if leather be 
 present in the substance examined, a purple color will soon ap- 
 pear, if a few drops of this solution be added to the alkaline solu- 
 tion of the leather extract. I prepared the phosphoric acid solu- 
 tion of phosphate of iron as follows : Ten grams of ferric chloride 
 were dissolved in water and sodium phosphate added till all the 
 iron was precipitated as phosphate of iron. The phosphate of 
 iron must be freshly prepared, otherwise it will dissolve slowly, 
 if at all. The phosphate of iron was filtered and washed quite 
 thoroughly with water, and both filter and precipitate brought into 
 a beaker containing 400 c.c. of water to which had been added 
 40 grams of glacial phosphoric acid. A gentle heat dissolves the 
 iron phosphate quite readily. 
 
 If a drop of pyrogallic acid is added to water, the solution 
 made slightly alkaline with ammonia, and then a cubic centimeter 
 of the iron phosphate solution added, a dark purple color appears. 
 If tannic acid is substituted for the pyrogallic acid, a dark wine 
 color results. In order to recognize leather in a mixture, a small 
 amount (i gramme) of the substance supposed to contain it, is 
 placed in a beaker with 30-40 c.c. of water, a few drops of sulfuric 
 acid added, the liquid brought to boiling, filtered, a little of the 
 iron phosphate solution added, and the solution then made slightly 
 alkaline with ammonia. If leather is present, a dark purple to 
 wine color will soon appear. 
 
 *Nortli Carolina Bxpt. Sta. Bull. No. 3, 1883 : Horn, Leather and Wool 
 Waste. 
 
loo Agricultural Science. Vol. viii. No. 3. 
 
 Should leather be present in a mixed fertilizer containing solu- 
 ble phosphate of lime, the latter will of course be precipitated on 
 the addition of ammonia, but this in no way interferes with the 
 color reaction. The writer examined during the summer of 1893 
 quite a number of fertilizers ofiScially collected in Massachusetts, 
 but in no case was leather to be detected. When, however, 10 
 per cent, of leather was added to a mixed fertilizer, and then 
 tested with the phosphate of iron solution, the dark color, due to 
 the presence of tannic or gallic acids very distinctly appeared. 
 
 During the early summer of 1893 several samples of leather 
 were received at the station. It was stated that large quantities 
 of the material were on the market, and one could surmise at 
 least that it might be used as a source of nitrogen in the manu- 
 facture of commercial fertilizers, organic nitrogen at the time 
 being quite high in price. It was thought wise to submit the 
 samples to several tests, and for the sake of comparison, pure 
 sole leather obtained by the writer at the cobbler's, and dried 
 blood were also included. 
 
 Description of the Samples. 
 
 I. Sole leather. 
 
 This leather was ground fine for future tests. Under the micro- 
 scope it showed a distinct fibrous structure. It contained 2.76 
 per cent, of fat and 7.94 per cent, of nitrogen. 
 
 II. Steamed leather. 
 
 Some of the finely ground leather was placed in pressure bot- 
 tles, water added, and heated for 6 hours at 110° C. The leather 
 was virtually subjected to three atmospheres of steam pressure. 
 After treatment it had become very dark in color and appeared as a 
 jelly-like, amorphous mass. The microscope showed it to be de- 
 void of any fibrous structure. The tannic or gallic acids were 
 still easily recognized, showing that they had not been destioyed 
 by the heat and pressure. When dry, it became quite brittle, 
 crumbling easily. 
 
 III. Coarse leather sent to the station. 
 
 This leather came in pieces, from the size of a walnut to that 
 of a small hen's egg. It contained 37,47 per cent, of fat and 4.52 
 per cent, of nitrogen. The large amount of fat completely con- 
 cealed its structure. 
 
i894- Agricultural Science. ioi 
 
 IV. Philadelphia Tankage. 
 
 The sample was very finely ground and quite dry. It con- 
 tained 1.95 per cent, of fat, 7.80 per cent, of nitrogen and traces 
 only of phosphoric acid. Its smell and general appearance indi- 
 cated clearly that it was leather that had been roasted or steamed. 
 To the eye it appeared to be lacking in fibrous structure, and 
 with the microscope it appeared simply as a gelatinous mass. 
 
 V. Dried blood. 
 
 It was an excellent sample, containing 12.71 per cent, of nitro- 
 gen and 0.64 per cent, of fat. 
 
 Artificial Digestion of Different Leathers. 
 
 The artificial digestion of the substances above described was 
 carried out according toStutzer's method. In the first series of 
 trials both the pepsin and pancreas solutions were used. The 
 preparation of the pepsin solution has already been described. 
 
 The pancreas solution was prepared by taking the fresh pan- 
 creas of an ox, cutting it fine, mixing it with sand and allowing 
 it to stand 24 to 36 hours exposed to the air. It was then rubbed 
 with lime water and glycerine (to every 1,000 gm. of the pan- 
 creas-sand mixture use 3 litres of lime water and one litre of gly- 
 cerine of 1.23 sp. gr.), and the resulting fluid allowed to stand 
 with occasional stirring for five days. It was then filtered through 
 cloth to remove the coarse portions, heated to 40° C. for two hours, 
 and finally filtered through folded filters, and preserved in bottles. 
 To prepare the pancreas solution used in the process of digestion, 
 250 c.c. of the above described solution were mixed with 750 
 c.c. of soda solution. The soda solution contained 5 grammes of 
 carbonate of soda dissolved in 750 c.c. of water. The pancreas 
 solution thus prepared was heated for one to two hours at 37-40° 
 C, filtered to remove any flocky precipitate and one hundred c.c. 
 used for each test. 
 
 The results of the pepsin-pancreas digestion were as follows : 
 
 Per cent, of nitro- 
 gen digested. 
 
 I. Sole leather finely ground 80.98 
 
 II. Same leather after being heated 6 hours at 110° C. in 
 
 pressure bottles with water 97-23 
 
 III. Coarse leather (free from fat) 52.00 
 
 IV. Philadelphia tankage 90.64 
 
 V. Dried blood 99-13 
 
I02 AgRICULTURAI< SciENCK. Vol. VIII. No. 3. 
 
 The above results are all very high, but this is not surprising, 
 for the action of dilute alkalies on leather is well known and has 
 been several times referred to. In the present case, after the var- 
 ious leathers had been submitted to the pepsin digestion, there 
 appeared to be no very great change either in their appearance 
 or bulk. Blood on the other hand was nearly all dissolved by 
 the pepsin solution. As soon, however, as the leathers were sub- 
 mitted to the action of the pancreas solution a decided change 
 was noted. The solution became quite dark in color and the 
 larger part of the leather went into solution. While this method 
 indicated a greater availability on the part of the sole leather 
 after it had been submitted to steam pressure it nevertheless did not 
 give a correct idea of the digestibility and consequent availability 
 of the leather when compared with the dried blood. 
 
 The substances were therefore submitted to the action of the 
 pepsin solution alone with results as follows : 
 
 Percentage digesti- 
 bility of nitrogen. 
 
 I. Sole leather, i3-7o 
 
 II. Sole leather after steam pressure 34-40 
 
 III. Coarse leather 
 
 IV. Philadelphia tankage 42.30 
 
 V. Dried blood. 97.8o 
 
 These results coincide very closely with those obtained by other 
 investigators. The sole leather itself proved very indigestible. 
 It is possible that it might have proved somewhat less so if no 
 hydrochloric acid had been added during the digestion.* The sole 
 leather after being subjected to the action of the steam pressure 
 had a digestibility of 34.40 per cent., which coincides with re- 
 sults obtained by others for prepared leather as the following 
 samples show : 
 
 Percentage of nitro- 
 gen digested. 
 
 Leather cooked and roasted (Stutzer) 39«i9 
 
 Roasted leather meal ( Shepard and Chazal) 37 .80 
 
 Leather by benzine process (Johnson) 35-90 
 
 Leather by superheated steam (Johnson) 33-30 
 
 While then the action of steam and heat renders the leather 
 somewhat more digestible and probably more available in the soil, 
 it still has a digestibility below 50 per cent. Only the very poor- 
 est kinds of animal matter reach this low figure (50). The so 
 called Philadelphia tankage was also below 50 per cent, digestible 
 
 * Conn. Exp. feta., 1886, p. 122. 
 
1894. Agriculturaiv Scidnck. 103 
 
 and may be classified with the steamed or roasted leathers as re- 
 gards its value. 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 Raw, Roasted or Steamed 
 
 Leather. 
 
 The results of the combined experiments in the field and in pots 
 together with artificial digestion experiments, and nitrifica- 
 tion 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 Masachusetts 
 fertilizer law distinctly forbids it to be thus utilized. Carefully 
 conducted experiments by Wagner give it a relative value 
 of 20, nitrate of soda being equal to 100. From the mass of evi- 
 dence at our command it would seem that this figure about ex- 
 presses its relative worth as a direct source of plant food. If it 
 is offered for sale as a fertilizer, it should be sold as leather. 
 When nitrogen in organic matter has a value of 16 to 18 cents 
 per pound, nitrogen in raw, steamed or roasted leather should 
 be worth but 3 to 6 cents per pound. 
 
 The Action of Sulfuric Acid on Leather. 
 
 D eh era in and others suggest that if leather be dissolved in 
 sulfuric 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 un- 
 derstood 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 grammes of 50° B. sulfuric acid were heated in a 
 porcelain dish over a waterbath to about 90° C. and 12 grammes 
 of leather gradually added. A dark, thick fluid resulted. Thirty 
 c.c. of water were then added to dilute the thick fluid somewhat. 
 
I04 AgrICUI.TURAI< SCII;nCE. Vol. VIII. No. 3. 
 
 and bone ash was employed to dry off the resulting semi-fluid 
 mass. One hundred and thirty-six grammes of superphosphate 
 were obtained, which gave no tannic acid reaction. 
 
 Experiment II. 
 
 To 30 grammes of 50° B. sulfuric acid heated as above described, 
 were added 12 grammes of leather. A dark, thick paste was ob- 
 tained, to which were added 25 c.c. of water, and 33 grammes of 
 bone ash. Seventy-three grammes of superphosphate were ob- 
 tained. The reaction of tannic acid was not strong. 
 
 Analyses of the two products were made as follows : 
 
 I. 11. 
 
 Per cent. Per cent. 
 
 Moisture 18.03 15-59 
 
 Soluble phosphoric acid 14.84 11.80 
 
 Reverted " " .69 1.50 
 
 Insoluble " " 1.43 3.38 
 
 Total " " 16.96 16.68 
 
 Nitrogen 0.70 1.20 
 
 Experiments III, IV, V, VI. 
 
 The previously described Philadelphia tankage was used in 
 these experiments, and South Carolina floats in place of bone ash. 
 The objects in view were to see (a) how much leather could be 
 used without giving a tannic acid reaction, (b) to note if possible 
 to what extent the leather interfered with the action of the sul- 
 furic acid upon the floats, (c) to notice the approximate percent- 
 age of available phosphoric acid and nitrogen resulting, (d) to see 
 if any nitrogen in the resulting superphosphates was soluble in 
 water, (e) to note the amount of nitrogen in the superphosphate 
 artificially digestible by Stutzer's solution. To make this latter 
 estimation (e), 5 grammes of superphosphate were stirred with 
 water, filtered, and washed till the wash water was no longer 
 acid. The portion not soluble in water was treated with pepsin 
 solution. 
 
 Experim-ent III. 
 
 To 30 grammes of 50° B. sulfuric acid after heating, previously 
 described, were added 12 grams of Philadelphia tankage. A 
 thick, black dough resulted. It was diluted with 25 c. c. of 
 water, appearing then as a thick black fluid. To this fluid were 
 added 60 grammes of floats. The resulting superphosphate, after 
 
l894- AgRIC"UI<TURAL SCIEJNC:^. IO5 
 
 drying in the air for 24 hours, weighed 102 grammes. The tannic 
 acid reaction was quite strong. 
 
 Experhnent IV. 
 
 To 30 grammes of 50° B. acid were added 25 c. c. of water and 
 70 grammes of floats. The dry superphosphate weighed 10 1.5 
 grammes. 
 
 Experiment V. 
 
 To 30 grammes of 50° B. acid were added 9 grammes of Phil- 
 adelphia tankage, which resulted in a medium thick paste. 
 Twenty c. c. of water and 48.5 grammes of floats were afterwards 
 added. The dry superphosphate weighed 88 grammes, and gave 
 no tannic acid reaction. 
 
 Experiment VI. 
 
 To 30 grammes of 40° B, acid 9 grammes of Philadelphia tankage 
 were added, resulting in a medium thick paste. This paste was 
 diluted with 20 c, c. of water, and 50 grammes of floats were put 
 in. Seventy-nine grammes of superphosphate were obtained, 
 which gave a strong tannic acid reaction. 
 
 These several products were analyzed. 
 
 III. IV. V. VI. 
 
 Per cent. Per cent. Per cent. Per cent. 
 
 Moisture 14.14 I4-I3 14.86 
 
 Soluble phosphoric acid 6.78 7.30 7.80 
 
 Reverted " " 1.22 1.60 0.44 
 
 Insoluble " " 5.50 6.66 4.94 
 
 Total " " 13.50 15.56 13.18 
 
 Total nitrogen 0.81 0.87 1.03 
 
 Nitrogen after artificial digestion 0.37 0.25 0.41 
 
 Per cent, of total nitrogen digested 54 71 60 
 
 Soluble nitrogen trace trace 
 
 It would appear that 9 grammes of leather were all that could 
 be added to 30 grammes of sulfuric-acid without getting the 
 tannic-acid reaction. When, as in Experiment III., 12 grammes 
 of leather were added, the reaction for tannic acid was quite 
 marked, and the nitrogen in the superphosphate had a digestibil- 
 ity of but 54 per cent. Experiment VI. indicates that 40° B. 
 sulfuric acid was not quite strong enough to thoroughly disinte- 
 grate the 9 grammes of leather, for the tannic acid in the super- 
 phosphate was easily recognized, and the nitrogen was but 60 
 per cent, digestible. When 9 grammes of the Philadelphia tank- 
 
io6 Agricui.turai< Science. Vol. viii. No. 3. 
 
 age were dissolved in 30 grammes of 50° B. acid, no tannic acid 
 could be recognized, and 70 per cent, of the total nitrogen was 
 digestible. This is probably the average percentage of organic 
 nitrogen that would be found digestible in mixed fertilizer, as 
 offered for sale in our markets. Such a result is quite encourag- 
 ing. It would seem from the analysis of IV. that the leather had 
 not seriously interfered with the action of the sulfuric acid upon 
 the floats. We have in the four experiments above cited, added 
 rather too much phosphate rock and water, and in the two follow- 
 ing experiments, less were added. 
 
 Experiment VII. 
 
 To 30 grammes of 50° B. acid 9 grammes of Philadelphia tank- 
 age were added, and then 12 c.c. of water. To the thick fluid 
 resulting, 41 grammes of floats were added. After standing 24 
 hours, the material could be easily handled, and weighed 71.5 
 grammes. 
 
 Experiment VIII. 
 
 To 30 grammes of 50° B. acid 9 grammes of Philadelphia tank- 
 age were added, producing a thick pasty mass. Without the 
 addition of water, 28 grammes of floats were stirred in, and after 
 24 hours, the mass weighed 63 grammes. The phosphate was 
 quite black in color, and sticky. It needed at least 5 to 7 grammes 
 more floats, before it could be easily handled. It was plain that 
 the sulfuric acid was not all neutralized. If no water were added 
 to dilute the thick pasty mass, it would be very difficult to work 
 in the floats should large quantities be mixed. 
 
 ANAI^YSES. 
 
 VII. vin. 
 
 Per cent. Per cent. 
 
 Moisture 17-95 16.95 
 
 Soluble phosphoric acid 6.79 5.99 
 
 Reverted " " 2.16 1.62 
 
 Insoluble " " 1-94 1-56 
 
 Total " " 10.89 9-17 
 
 Total nitrogen 0.90 1,06 
 
 In Experiment VII., 8.95 per cent, of available phosphoric acid 
 was obtained, with but 1.94 per cent, of insoluble acid, and 0.90 per 
 cent, of nitrogen ; the phosphate was also in good mechanical 
 condition and gave no tannic acid reaction. The proportions of 
 water, sulfuric acid, floats, and leather, appear to be about correct, 
 
1894. Agricultural SeiENCE. . 107 
 
 and the percentages of available phosphoric acid and nitrogen as 
 high as could be expected, with floats as a dryer. 
 
 Experiment IX. 
 
 In Experiments III to VIII Philadelphia tankage was used as 
 a source of leather. 
 
 In this experiment, pure, fine ground sole leather was used, 
 to see if the sulfuric acid acted as strongly upon the pure 
 leather, as upon the prepared article. To 30 grammes of 50 B. 
 acid were added 9 grammes of sole leather, 20 c.c. of water, and 
 60 grammes of floats. 
 
 The resulting phosphate weighed 98.5 grammes 
 
 Analysis gave the following results : 
 
 Per cent. 
 
 Total nitrogen in the superphosphate 0.71 
 
 " " after digestion 0.22 
 
 " " digested per cent 69. 
 
 Nitrogen soluble in water 0.047 
 
 Percent, of soluble nitrogen 6.62 
 
 No tannic acid could be detected in this superphosphate. The 
 digestion test was made in triplicate, and showed that the pure 
 sole leather, after treatment with sulfuric acid, was quite as di- 
 gestible as the steamed or roasted leather after a similar treat- 
 ment, and as digestible as the average animal matter sold for 
 fertilizing purposes. 
 
 In order to still further study the value of dissolved leather as 
 a source of plant food, pot experiments are now in progress at 
 the station, and the results will be reported later. 
 
 Practical Deductions. 
 
 The various experiments made would indicate that leather, sul- 
 furic-acid, water and floats should be mixed in about the fol- 
 lowing relative proportions : 
 
 2,000 lbs. 50° B. sulfuric acid 
 
 600 " ground leather 
 
 800 " water 
 2,700 " floats 
 
 The resulting mixture, when in fairly dry condition, would 
 weigh approximately 5,000 lbs., shrinking about 18 to 20 per 
 cent. It would have approximately the following composition : 
 
io8 Agricultural Science. Vol. viii. No. 3. 
 
 Per cent. 
 
 Moisture 18.00 
 
 Available phosphoric acid 8.50 
 
 Insoluble " " 2.00 
 
 Total " " 10.50 
 
 " nitrogen 0.90 
 
 Two thousand pounds of sulfuric acid will not take up more than 
 600 lbs. of leather and render the leather 70 per cent, digestible. 
 If more is added, part of the latter, whether roasted or raw, will 
 not be thoroughly acted upon by the acid. With 600 lbs. of 
 leather, a thick paste results which must be diluted somewhat 
 with water in order to allow the sulfuric acid to act freely upon 
 the floats. If bone ash should be used as a dryer in place of 
 ground phosphate rock a higher percentage of available phos- 
 phoric acid and of nitrogen would result, as Experiments I and II 
 indicate. 
 
 Before submitting the leather to the action of the sulfuric-acid, 
 it would undoubtedly be better, after extracting the fat, to steam 
 or roast it, in order that it may be easily pulverized. Raw. un- 
 treated leather is ground only with difi&culty, and if the mechani- 
 cal condition of the leather were poor, the action of the sulfuric 
 acid would be imperfect 
 
 Resume— Action of Sulfuric Acid Upon Leather. 
 
 Artificial digestion experiments show that the nitrogen in either 
 untreated, steamed or roasted leather after being acted upon by 
 sulfuric acid has a digestibility of 70 per cent. If pot and field 
 experiments corroborate the digestion experiments, it would 
 make plain that the nitrogen in leather after being thus treated 
 would be as available as a Source of plant food as the nitrogen in 
 the average fish, blood, etc. 
 
 Whether it would be practicable from an economical standpoint 
 to thus utilize the leather waste is of course another question 
 which must be answered by practical experiments, 
 
 Mass. State Experiment Station, 
 April, 1894. 
 
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