/ 
 
 r.^o 
 
 \S 
 
 Issued December 31, 1913, 
 
 HAWAII AGRICULTURAL EXPERIMENT STATION, 
 
 E. V. WILCOX, Special Agent in Charge. 
 
 Bulletin No. 30. 
 
 THE EFFECT OF HEAT ON 
 HAWAIIAN SOILS. 
 
 BY 
 
 W. P. KELLEY, 
 
 Chemist, 
 
 AND 
 
 UNIV. OF Fl 
 DOCUMENTS DFPT 
 
 WILLIAM McGEORGE 
 
 Assistant Chemist. 
 
 > 
 
 DEPOSITORY 
 
 UNDER THE SUPERVISION OF 
 OFFICE OF EXPERIMENT STATIC 
 
 U, 8. DEPARTMENT OF AGRICULTURE 
 
 
 ***** 
 
 ~.<"' 
 
 WASHINGTON: 
 
 GOVERNMENT PRINTING OFFICE. 
 
 1913. 
 
Issued Decern ber 31, 1913, 
 
 HAWAII AGRICULTURAL EXPERIMENT STATION, 
 
 E. V. WILCOX, Special Agent in Charge. 
 
 Bulletin No. 30. 
 
 THE EFFECT OF HEAT ON 
 HAWAIIAN SOILS. 
 
 BY 
 
 W. P. KELLEY, 
 
 Chemist, 
 
 AND 
 
 WILLIAM McGEORGE, 
 
 Assistant Chemist. 
 
 UNDER THE SUPERVISION OF 
 OFFICE OF EXPERIMENT STATIONS, 
 
 U. S. DEPARTMENT OF AGRICULTURE. 
 
 WASHINGTON: 
 
 GOVERNMENT PRINTING OFFICE. 
 
 1913. 
 
HAWAII AGRICULTURAL EXPERIMENT STATION, HONOLULU. 
 
 [Under the supervision of A. C. True, Director of the Office of Experiment Stations, 
 United States Department of Agriculture.] 
 
 Walter H. Evans, Chief of Division of Insular Stations, Office of Experiment Stations. 
 
 STATION STAFF. 
 
 E. V. Wilcox, Special Agent in Charge. 
 J. Edgar Higgins, Horticulturist. 
 
 W. P. Kelley, Chemist. 
 
 C. K. McClelland, Agronomist. 
 
 D. T. Full aw ay, Entomologist. 
 
 W. T. McGeorge, Assistant Chemist. 
 Alice R. Thompson, Assistant Chemist. 
 C. J. Hunn, Assistant Horticulturist. 
 V. S. Holt, Assistant in Horticulture. 
 C. A. Sahr, Assistant in Agronomy. 
 
 F. A. Clowes, Superintendent Hawaii Substations. 
 W. A. Anderson, Superintendent Rubber Substation. 
 J. de C. Jerves, Superintendent Homestead Substation. 
 Joseph K. Clark, Superintendent Waipio Substation. 
 George Copp, Superintendent Kula Substation. 
 
 (2) 
 
 ADDITIONAL COPIES of this publication 
 -TA may be procured from the Superintend- 
 ent of Documents, Government Printing 
 Office, Washington, D. C, at 10 cents per copy 
 
LETTER OF TRANSMITTAL. 
 
 Honolulu, Hawaii, August 15, WIS. 
 Sir: I have the honor to submit herewith and recommend for 
 publication, as Bulletin 30 of the Hawaii Agricultural Experi- 
 ment Station, a paper dealing with the Effect of Heat on Hawaiian 
 Soils, by W. P. Kelley, chemist, and William McGeorge, assistant 
 chemist of the station. The effect of heat upon Hawaiian soils, 
 including highly manganiferous soils, has been found to be decidedly 
 beneficial to the growth of all kinds of plants. The careful study 
 of the various chemical and mechanical changes produced in soils 
 by the application of heat, as set forth in this bulletin, throws con- 
 siderable light upon the reasons for this beneficial effect. Studies 
 on the effects of heat on soils have usually been confined to a few 
 plant-food elements, whereas in this bulletin a large number of the 
 inorganic and organic substances are considered. The bulletin is, 
 therefore, considered a distinct contribution to the literature of this 
 interesting phase of soil work. 
 
 Respectfully, E. V. Wilcox, 
 
 Special Agent in Charge. 
 Dr. A. C. True, 
 
 Director Office of Experiment Stations, 
 
 U. S. Department of Agriculture, Washington, D. C. 
 
 Publication recommended. 
 A. C. True, Director, 
 
 Publication authorized. 
 D. F. Houston, 
 
 Secretary of Agriculture . 
 (3) 
 
CONTENTS. 
 
 Page. 
 
 Introduction 5 
 
 The effects of heat on the solubility of inorganic constituents 7 
 
 Preliminary work 9 
 
 Method of preparing extracts 11 
 
 Soil types 12 
 
 Silica 13 
 
 Alumina 14 
 
 Iron 15 
 
 Manganese 16 
 
 Lime and magnesia 18 
 
 Potash 20 
 
 Phosphoric acid 21 
 
 Sulphates 22 
 
 Bicarbonates 23 
 
 Effect of heat upon rice and taro soils 24 
 
 Discussion 25 
 
 The effects of heat on soil nitrogen 28 
 
 Introduction 28 
 
 Effects of heat on nitrates 31 
 
 Effects of heat on the ammonia content 32 
 
 Effects of brush burning in the field 33 
 
 Effects of heat on the organic nitrogen 34 
 
 Summary 37 
 
 (4) 
 
THE EFFECT OF HEAT ON HAWAIIAN SOILS. 
 
 INTRODUCTION. 
 
 Heat as a means of stimulating crops has been made use of in cer- 
 tain European countries for centuries. The burning of moorlands 
 and the paring and burning of heavy clay sods were extensively prac- 
 ticed in times past. Although their use at present is by no means as 
 common as formerly, these practices have not been entirely aban- 
 doned. The adoption of more intensive methods of farming, the 
 use of fertilizers, cost of fuel, recognition of the serious destruction 
 of the organic matter, and the demand for a more continuous use of 
 the land have brought about the gradual disuse of these ancient 
 practices. 
 
 In America soil burning, in the sense it is understood in Europe, 
 has never been made use of extensively. In connection with certain 
 crops demanding early forcing, however, soil burning is practiced 
 well-nigh universally. The seed of tobacco, cabbage in some locali- 
 ties, and some other crops that are grown from transplanted seedlings 
 are still sown in soil which has been previously burned. In prepar- 
 ing seed beds for tobacco the soil is frequently burned heavily, usually 
 a strong wood * fire being maintained on the bed for several hours. 
 It is a matter of common observation that the growth of seedlings 
 on the burned soil is usually superior to that on the surrounding 
 unburned land. The effects of burning are by no means confined to 
 the germination and growth of seedlings. In newly cleared lands 
 crops of various kinds usually grow more rapidly and produce 
 increased harvests on the spots where brush or log heaps have been 
 burned, and often the effects persist through two or more years. 
 
 In Hawaii the growth of certain crops is enormously influenced by 
 the mere burning of small accumulations of brush and undergrowths 
 of guava and lantana. The effect on cotton on the uplands of Oahu 
 produced by these small fires may represent the difference between 
 success and failure. The color and vigor of the crop on these small 
 areas dotted here and there over a field attract attention. Other 
 crops are affected similarly. 
 
 1 Oil and gas are sometime; used for this purpose. 
 (5) 
 
6 
 
 It has been known for a long time that burning improves the struc- 
 ture of clays by causing a coalescence of the smaller particles into 
 larger granules, thus effectively improving the drainage. The in- 
 creased size of the pores and air spaces within the soil permits of better 
 aeration and encourages deeper root development. By means of heat 
 the hydrous compounds become dehydrated, plasticity and adhe- 
 siveness are overcome, the movement of soil moisture facilitated, and 
 a more congenial environment for root development is produced. 
 If sufficiently great heat be employed, the clay may be baked into 
 hard lumps, which yield to cultural and weathering influences with 
 difficulty, and, therefore, injury may result. In any event the 
 dehydrated silicates and oxids return very slowly to their former 
 state and the crumb structure induced by the heat persists for years- 
 The physical effects of heat on clays are so pronounced that the 
 admixing of a few tons per acre of the burnt with the natural soil 
 was formerly employed in Europe as a means of ameliorating heavy 
 clay lands. 
 
 Regarding the chemical effects of burning it is also well known that 
 clay soils undergo chemical changes. In general the solubility of 
 aluminum and potassium in acids is greatly increased up to a certain 
 temperature, beyond which a decrease sets in. It is generally held 
 that under the influence of high temperatures, especially with the aid 
 of oxidizing conditions, a wasteful destruction of soil organic matter 
 and consequent loss of nitrogen takes place. 
 
 In addition to the above-named physical and chemical effects the 
 killing of weed seeds, parasitic fungi, disease-producing organisms, 
 and insects are generally looked upon as being among the beneficial 
 effects of soil burning. 
 
 While the old system of burning the soil has gradually fallen out of 
 use, the closely related partial sterilization by means of heat and vola- 
 tile antiseptics is of great interest at the present time. In greenhouse 
 work steam sterilization finds extensive application and has been the 
 subject of interesting investigations during the past few years. 
 Likewise the action of dry heat in its relation to partial sterilization 
 and in comparison with the effects of volatile antiseptics on subse- 
 quent biological activities has received considerable study. The 
 old idea of considering the subject in a restricted physical and limited 
 chemical sense is, therefore, giving way to a broader view of the 
 question. The more specific chemical effects involved, including cer- 
 tain physico-chemical effects dealt with more in detail in this paper, 
 and the biological results are now being studied. 
 
 It has been found that moderate temperatures bring about an 
 increase in the solubility not only of the mineral constituents of soils 
 but also in the organic matter. Furthermore, a number of investi- 
 gators have found that steam sterilization, particularly when under 
 
pressure, frequently produces a condition that is toxic both to the 
 germination and the subsequent growth of plants. Usually the toxic 
 condition is of short duration and the growth of crops seems to aid 
 effectively in overcoming it. There are many phases of this question 
 that are not fully understood. 
 
 There are two characteristics of Hawaiian soils that give them 
 special interest in this connection, (1) the peculiarities and the high 
 proportion of the clay; (2) the inertness of the unplow r ed and unbroken 
 sod lands. The former gives special interest to the question of heat- 
 ing from the physical point of view, and the latter is of interest to the 
 question because of its bearing on soil aeration. With but few excep- 
 tions it is necessary to plow T the land, following with thorough tillage 
 at frequent intervals for several months before planting. A field 
 plowed for the first time, although the soil be thoroughly pulverized 
 and reduced to a state of fine tilth, usually will not support plant 
 growth satisfactorily. The farmers of Hawaii have found it neces- 
 sary to aerate newly plowed lands for a period of several months 
 before planting the first crop. It has been observed, however, that 
 excellent growth of crops is obtained on the small spots where brush 
 was burned and without the continued aeration above referred to. 
 Heat, therefore, seems to accomplish in the soil effects similar to those 
 brought about by aeration. The application of fertilizers produces 
 no such effects. 
 
 In connection with a general study of soil aeration the authors 
 have, therefore, been led to a study of the effects of heat on these 
 soils. The present paper deals with one phase of this question, the 
 physico-chemical changes produced. In the first part are presented 
 the data obtained with reference to the solubility of the inorganic 
 constituents and in the second part are some data of a more or less 
 empirical nature on the grosser effects of heat on soil nitrogen. 
 
 THE EFFECTS OF HEAT ON THE SOLUBILITY OF INORGANIC 
 
 CONSTITUENTS. 
 
 While a considerable number of investigators have studied the 
 question of the effect of heat upon the solubility of phosphoric acid, 
 using various solvents, apparently few have gone beyond this and 
 determined its effect upon the solubility of the remaining mineral 
 constituents commonly occurring in soils. In fact, with few excep- 
 tions, the entire stress has been laid upon the three elements generally 
 considered to be of greatest plant-food value, namely, nitrogen, phos- 
 phoric acid, and potash. 
 
 In most instances the results of these earlier investigations have 
 shown an increase in solubility of phosphoric acid, with increase in the 
 temperature to which the soils have been heated. M. Xagaoka, 1 on 
 
 > Bui. Col. Agr., Tokyo Imp. Univ., 6 (1904), No. 3, p. 263. 
 
8 
 
 igniting soils for 15 minutes to remove humus, found an increase in 
 solubility of phosphoric acid, which, he concluded, was due to the de- 
 struction of organic matter with which the phosphoric acid was 
 combined. He used as solvents, hydrochloric acid, specific gravity 
 1.15, distilled water, and several of the weaker organic acids. Stewart * 
 used Schmoeger's method of determining the increase of solubility 
 in 12 per cent hydrochloric acid before and after ignition, as an 
 indication of the phosphoric acid combined with organic matter. 
 Fraps, 2 while finding an increase in the solubility of phosphoric acid 
 on ignition, considers that this increase is not wholly due to organic 
 phosphorus, but that mineral phosphates in soils are also rendered 
 more soluble by ignition, thereby rendering the ignition method an 
 unsuitable one for determining organically combined phosphorus. 
 On the other hand, Lipman 3 found while working on a series of Cali- 
 fornia soils, that heating decreased the solubility of phosphoric acid 
 in strong nitric acid. Peterson 4 found that the solubility increased 
 rapidly with increase in temperature from 130° up to 200° C, but 
 that the solubility of the mineral phosphates in soils was not increased 
 by heating below 240° C. 
 
 Valuable work on the solubility of the mineral constituents of 
 soils is to be found among the publications of the Bureau of Soils, the 
 work being confined largely to the use of water as solvent. In a 
 bulletin of that bureau, 5 King gives comparative results of work upon 
 fresh and oven-dried soils which show the effect of heating to 110° C. 
 to be striking. On the average more nitrates, phosphoric acid, sul- 
 phates, bicarbonates, and silica were recovered from the oven-dried 
 soils than from the fresh samples, while the average of the chlorin 
 determinations showed a decrease. No determination of the basic 
 constituents are tabulated, but King states that upon later investi- 
 gations he found an increase in potash, lime, and magnesia in oven- 
 dried soils. He makes several suggestions as to the cause of this in- 
 crease, both from a physical and chemical standpoint, but it is evident 
 from his discussions that he considered the cause to be primarily 
 physical. A number of other investigators have noted an increase 
 in total inorganic matter soluble in water 6 as a result of heating, 
 but no separation of the elements was made. 
 
 The special phase to which this paper is devoted is that of the effect 
 of heat upon the solubility of the mineral constituents, distilled water 
 and fifth-normal nitric acid being used as solvents. 
 
 i Illinois Sta. Bui. 145. 
 2 Texas Sta. Bui. 136. 
 
 * Jour. Indus, and Engin. Chem., 4 (1912), No. 9, p. 663. 
 
 * Wisconsin Sta. Research Bui. 19. 
 
 * U. S. Dept. Agr., Bur. Soils Bui. 26, p. 55. 
 6 New York Cornell Sta. Bui. 275. 
 
PRELIMINARY WORK. 
 
 The results of some preliminary experiments on three Hawaiian 
 soils dealing with the various methods of preparing soil extracts with 
 distilled water are presented in the following table: 
 
 Influence of state of moisture and time of extraction on composition of the water extract 
 
 of soils. 
 [In parts per million of dry soil.] 
 
 
 Length 
 of ex- 
 traction. 
 
 Bicar- 
 
 bo- 
 
 nates 
 
 (HC0 3 .) 
 
 Iron 
 oxid 
 and 
 alu- 
 mina 
 
 (Fe 2 3 
 and 
 
 A1 2 3 ). 
 
 Phos- 
 phoric 
 
 acid 
 (P 2 4 ). 
 
 Man- 
 ganese 
 oxid 
 (Mn 3 
 4 ). 
 
 Lime 
 (CaO). 
 
 Mag- 
 nesia 
 (MgO). 
 
 Sul- 
 phuric 
 
 acid 
 (S0 3 ). 
 
 Potash 
 (K 2 0). 
 
 Soil No. 313: 
 
 Fresh 
 
 Air dried 
 
 Oven dried 
 
 Fresh 
 
 1 hour... 
 
 ...do 
 
 ...do 
 
 24 hours. 
 
 ...do 
 
 ...do 
 
 7 days... 
 
 ...do 
 
 ...do 
 
 1 hour... 
 
 ...do 
 
 ...do 
 
 24 hours. 
 
 ...do 
 
 ...do 
 
 7 days... 
 
 ...do 
 
 ...do 
 
 1 hour... 
 ...do 
 
 ...do 
 
 155.0 
 1, 040. 
 358.0 
 95.6 
 678.0 
 246.0 
 191.0 
 562.0 
 262.0 
 
 97.8 
 708.0 
 371.0 
 117.7 
 651. 
 228.0 
 157.0 
 688.0 
 180.0 
 
 140.0 
 975. 
 558.0 
 200.0 
 
 53.5 
 
 8.7 
 12.8 
 17.8 
 13.0 
 19.2 
 45.8 
 44.5 
 49.1 
 
 38.6 
 4.3 
 
 2.03 
 1.95 
 2.35 
 2.55 
 1.74 
 3.42 
 2.55 
 . 2.38 
 3.00 
 
 2.32 
 1.94 
 
 2.55 
 
 17.4 
 
 "2. 55* 
 15.20 
 
 "i5.'2" 
 88.9 
 
 2.5 
 27.4 
 
 122.2 
 
 121.8 
 197.0 
 148.0 
 
 86.8 
 120.0 
 
 96.9 
 160. 5 
 102.2 
 
 56. 5 
 77.2 
 89.0 
 77.0 
 43.0 
 85.0 
 71.9 
 47.2 
 63.8 
 
 127.6 
 224.0 
 194.1 
 197.6 
 103.2 
 123.5 
 206. 7 
 162.0 
 212.0 
 
 62.7 
 103. 
 159.0 
 
 77.6 
 102.0 
 126.2 
 
 68.3 
 168.0 
 116.0 
 
 14.8 
 105. 2 
 99.8 
 39.0 
 88.5 
 113.5 
 70.4 
 76.1 
 109.0 
 
 60.2 
 120.0 
 119.5 
 105.1 
 
 81.5 
 103.5 
 
 55.0 
 102.0 
 124.0 
 
 247.0 
 120.0 
 194.0 
 257.2 
 134.5 
 199.0 
 221.5 
 171.0 
 145.0 
 
 114.0 
 81.0 
 145. 
 175.6 
 72.0 
 131.0 
 137.1 
 83.8 
 151.0 
 
 137.1 
 105. 5 
 136.0 
 133. 7 
 
 67.2 
 133.0 
 155. 6 
 
 £3. 1 
 159.0 
 
 133.0 
 256.0 
 143.0 
 226.6 
 
 Air dried 
 
 Oven dried 
 
 Fresh 
 
 213.0 
 121.0 
 239.8 
 
 Air dried 
 
 Oven dried 
 
 Subsoil No. 314: 
 
 Fresh 
 
 282.0 
 61.0 
 
 150. 5 
 
 Air dried 
 
 Oven dried 
 
 142.0 
 64.1 
 
 Fresh 
 
 43.7 
 10.8 
 14.8 
 23.2 
 6.4 
 17.0 
 
 3.04 
 20.2 
 11.2 
 
 4.6 
 40.5 
 15.4 
 10.3 
 
 9.0 
 
 2.32 
 2.14 
 2.96 
 2.05 
 2.14 
 2.76 
 
 .76 
 1.80 
 7.05 
 1.37 
 1.80 
 3.31 
 1.06 
 2.02 
 
 5.1 
 30.1 
 
 "u.s" 
 
 17.2 
 
 1.52 
 15.70 
 
 '"4."6" 
 15.7 
 
 ""7.'6" 
 29.2 
 
 208.5 
 
 Air dried 
 
 Oven dried 
 
 Fresh 
 
 181.0 
 118.0 
 227.0 
 
 Air dried 
 
 Oven dried 
 
 Soil No. 319: 
 
 Fresh 
 
 158. 2 
 68.0 
 
 142.2 
 
 Air dried 
 
 Oven dried 
 
 Fresh 
 
 278.0 
 135.0 
 170.8 
 
 Air dried 
 
 Oven dried 
 
 p'resh 
 
 ...do 1,300.0 
 
 ...do 270.0 
 
 7 days...! 99.0 
 
 ...do 1,280.0 
 
 ...do 485.0 
 
 274.0 
 70.5 
 155.0 
 
 Air dried 
 
 Oven dried 
 
 234.0 
 147.0 
 
 
 
 
 
 
 
 
 The soils chosen were from the Koolaupoko district, on Oahu, 
 No. 313 being a sample of brown ferruginous clay soil which occurs 
 widely distributed in this district. It was very dry at the time of sam- 
 pling and was covered with a heavy growth of guava. No. 314 is the 
 subsoil to No. 313, and No. 319 is a sample of a similar type which 
 had been plowed and planted to pineapples. 
 
 The extracts were made by treating the soils with distilled water 
 in the proportion of 5 parts of the latter to 1 of the former in glass- 
 stoppered bottles, shaking occasionally during the period noted in 
 the table, each being shaken an equal number of times. The values 
 are figured to parts per million of the oven-dry soil. Sample No. 313 
 contained, originally, 18.65 per cent moisture, No. 314 19.65 per cent, 
 and No. 319 30.3 per cent. 
 
 It will be seen that in every case the air-dried soil contained the 
 largest amount of soluble HC0 3 , the oven-dried sample next, and the 
 fresh soil the least, regardless of the time of extraction. 
 14060°— Bull. 30—13 2 
 
10 
 
 No attempt was made to separate iron oxid and alumina, but the de- 
 termination seems to vary considerably in the different soils. No. 313 
 apparently increased in solubility with increase in time of extraction. 
 If the abnormal figure, 53.5, be disregarded, the difference between the 
 fresh, air-dried, and oven-dried soil is very slight. In the subsoil air 
 drying produced a decrease in solubility, but the oven-dried were 
 more soluble than the air-dried samples. The results from No. 319 
 are discordant, but indicate the air-dried form to be the most soluble. 
 
 Phosphoric acid. — This series is remarkably concordant and indi- 
 cates an increase in solubility of this constituent upon drying in the 
 oven and at the same time, without exception, shows an increase in 
 solubility with increase in time of extraction. 
 
 Manganese. — These results indicate an increase in solubility of 
 manganese with increase in time of extraction and also an increase in 
 solubility upon drying. Unfortunately the whole series of manganese 
 determinations on the oven-dried samples was lost through accident. 
 
 Lime. — While the results from the lime determinations are very 
 inconsistent, the general average tends to show an increase in solu- 
 bility upon heating in the oven and a maximum solubility in the one- 
 hour period of extraction. This latter may be due, however, to sub- 
 sequent precipitation in the longer extractions. 
 
 Magnesia. — The table shows a marked consistency, especially with 
 reference to the rate of increase in solubility of magnesia, due to 
 drying. The concentration of the extracts from the fresh soils was 
 least, with only one exception, while that from the oven-dried soils 
 was greatest in most instances. While there is considerable varia- 
 tion, the data indicate the most complete extraction in that of seven 
 days' duration. 
 
 Sulphuric acid. — The relative amounts of this constituent extracted 
 show it to be slightly more soluble in the fresh soil, judging from the 
 average of the series, although only slightly more so than in the 
 oven-dried soil, and that the concentration is practically the same 
 for the several periods of extraction. 
 
 Potash. — The potash series shows this element to be much more 
 soluble in the air-dry and fresh soils than in the oven-dried soils, 
 while there is scarcely any difference in the solubility as induced by 
 increasing the time of extraction from 24 hours to 7 days. 
 
 The above results tended to establish the advisability of an arbi- 
 trary extraction of not over 24 hours, and partly for this reason it was 
 decided that the method at present in general use, namely, shaking 
 for a period of 1 hour and allowing to settle for 24 hours would be 
 suitable to our conditions. Owing to the mechanical texture of 
 Hawaiian soils, caused by the presence in them of highly ferruginous 
 clays, which assume a colloidal form if worked when too wet, it was 
 found necessary to allow the extracts to settle and in every instance, 
 except when heated to 250° C. or ignited, it was necessary to add a 
 
11 
 
 coagulant. Not having the apparatus to effect a rapid filtration 
 through clay filters, small amounts of ammonium chlorid were used 
 to bring about coagulation of the clay and make filtration through 
 filter paper possible. In addition to using distilled water as a solvent, 
 fifth-normal nitric acid was chosen in order to gain additional infor- 
 mation concerning the action of different solvents. The means 
 chosen for drying the soils were in an air bath at 100° C, and 250° C, 
 over a Bunsen burner. It being practically impossible to obtain 
 ignition all the samples fresh, extraction upon the soils in this state 
 was not attempted. 
 
 METHOD OF PREPARING EXTRACTS. 
 
 The soils were prepared as follows: Upon receipt in the labora- 
 tory they were spread out to dry. After reaching an approximately 
 stable moisture content portions were weighed into porcelain dishes. 
 One series was dried in an oven at 100° C. for 8 hours continuously, 
 another treated likewise at 250° C, while the last series was heated 
 over a Bunsen burner, at first carefully on a wire gauze for 2 hours to 
 prevent dusting and then over the direct flame for 2 hours, thus 
 destroying practically all the organic matter. 
 
 Water extract. — This extraction was made by treating 200 gram 
 portions of the soils with 1 liter distilled water, shaking occasionally 
 for 1 hour, as previously mentioned, and then allowing to settle 24 
 hours, adding small amounts of ammonium chlorid as a coagulant 
 when necessary. Particular attention was given to these extrac- 
 tions in order that all the samples in each series of the same soil 
 should receive similar treatment as regards the number of times of 
 shaking, thus making the results more directly comparable. Like- 
 wise, all distilled water for a series was taken from the same lot in 
 order to eliminate any slight influence which varying amounts of car- 
 bon dioxid in the distilled water would have upon the solubility of 
 the minerals. After settling 24 hours the solution was filtered 
 through double filter papers and from this solution 500 cubic centi- 
 meters was evaporated to a small volume and used for analysis. 
 All determinations were made gravimetrically except phosphoric 
 acid, iron, and bicarbonate. The former was made colorimetrically 
 in 50 cubic centimeters of the original solution. 1 Iron was deter- 
 mined colorimetrically 2 in a solution of the ammonia precipitate 
 from the 500 cubic centimeters portion, and bicarbonate was de- 
 termined by titrating 50 cubic centimeters of the original solution 
 with twentieth-normal acid potassium sulphate, using methyl orange 
 as indicator. 
 
 Nitric acid extract. — The soils for this phase of the work were pre- 
 pared in the same manner as above described as regards tempera- 
 
 'U. S. Dept. Agr., Bur. Soils Bui. 31, p. 45. 
 «U. S. Dept. Agr., Bur. Soils Bui. 31, p. 38. 
 
12 
 
 tures and time of heating. However, in this work only 100 grams 
 were treated with 500 cubic centimeters fifth-normal nitric acid. The 
 extraction differed in that the soils were shaken occasionally, for a 
 period of 5 hours, and then filtered directly through double filter 
 papers. All determinations were made gravimetrically in 100 cubic 
 centimeters of this filtrate with the exceptions of iron, which was 
 determined volumetrically, and phosphoric acid and titanium, which 
 were determined colorimetrically in 25 cubic centimeter portions of 
 the original extract. 
 
 SOIL TYPES. 
 
 The types of soil selected for this work were of the widest possi- 
 ble range, and represented, in a general way, the normal and ab- 
 normal types, both physical and chemical, to be found in the islands. 
 The following table gives the chemical analyses of samples as deter- 
 mined with hydrochloric acid of specific gravity 1.115: 
 Chemical analyses of soils used. 
 
 Soil 
 No. 
 
 74. 
 
 Soil 
 No. 
 164. 
 
 Soil 
 No. 
 
 Soil 
 No. 
 292. 
 
 SoU 
 No. 
 290. 
 
 Soil 
 No. 
 405. 
 
 Soil 
 No. 
 416. 
 
 Soil 
 No. 
 417. 
 
 Soil 
 No. 
 406. 
 
 Soil 
 No. 
 
 428. 
 
 Soil 
 No. 
 426. 
 
 Soil 
 No. 
 448. 
 
 Moisture (H 2 0) 
 
 Volatile matter 
 
 Insoluble matter 
 
 Iron oxid (Fe 2 3 ) 
 
 Alumina (AI2O3) 
 
 Titanium oxid (Ti0 2 ) 
 
 Manganese oxid (Mn 3 04) . . . 
 
 Lime(CaO) 
 
 Magnesia (MgO) 
 
 Potash (K 2 0) 
 
 Soda(Na 2 0) 
 
 Sulphuric acid (SO3) 
 
 Phosphoric acid (P 2 Os) 
 
 P.ct 
 
 25.46 
 13.08 
 32.69 
 10.13 
 12.59 
 
 .13 
 
 2.63 
 
 1.09 
 
 .14 
 
 .34 
 
 .22 
 
 1.02 
 
 P.ct 
 1.22 
 3.56 
 
 48.17 
 30.58 
 
 3.05 
 
 1.72 
 .10 
 .12 
 
 1.22 
 .48 
 
 1.46 
 .44 
 .08 
 
 P.ct 
 
 5.36 
 
 16.78 
 
 31.67 
 
 18.60 
 
 14.67 
 
 .68 
 
 9.21 
 
 1.32 
 
 .52 
 
 .79 
 
 .38 
 
 .15 
 
 .20 
 
 P.ct. 
 
 7.65 
 
 8.42 
 
 38.49 
 
 16.63 
 
 12.85 
 
 2.00 
 
 .24 
 
 1.84 
 
 8.71 
 
 .39 
 
 1.36 
 
 .08 
 
 .57 
 
 P.ct. 
 
 8.44 
 
 15.80 
 
 40.02 
 
 16.41 
 
 14.11 
 
 1.50 
 
 .30 
 
 .77 
 
 1.30 
 
 .17 
 
 .42 
 
 .10 
 
 .27 
 
 P.ct 
 
 8.02 
 
 12.50 
 
 39.12 
 
 15.24 
 
 20.54 
 
 2.40 
 
 .15 
 
 .86 
 
 .99 
 
 .20 
 
 .48 
 
 .33 
 
 .44 
 
 P.ct. 
 
 6.17 
 
 17.73 
 
 36.09 
 
 13.20 
 
 20.39 
 
 1.60 
 
 3.84 
 
 .33 
 
 .44 
 
 .39 
 
 .59 
 
 .35 
 
 .20 
 
 P.ct. 
 
 16.26 
 
 17.53 
 
 30.92 
 
 11.24 
 
 19.38 
 
 1.40 
 
 2.85 
 
 .21 
 
 .36 
 
 .45 
 
 .36 
 
 .43 
 
 P.ct. 
 
 10.34 
 
 17.73 
 
 37.31 
 
 10.92 
 
 20.20 
 
 1.80 
 
 .06 
 
 .48 
 
 .67 
 
 .20 
 
 .48 
 
 .30 
 
 .48 
 
 P.ct 
 
 14.94 
 
 22.24 
 
 34.99 
 
 8.24 
 
 10.73 
 
 3.20 
 
 .20 
 
 1.91 
 
 2.24 
 
 .24 
 
 1.40 
 
 .45 
 
 .22 
 
 P.ct 
 
 10.47 
 
 18.28 
 
 24.80 
 
 22.52 
 
 19.10 
 
 3.80 
 
 .22 
 
 .15 
 
 .44 
 
 .28 
 
 .74 
 
 .39 
 
 .19 
 
 P.ct. 
 
 16.00 
 
 25.58 
 
 15.10 
 
 19.20 
 
 16.64 
 
 4.20 
 
 .06 
 
 .50 
 
 No. 74 is a yellowish-brown soil from Waimea, Hawaii, of sandy 
 silt texture, with an abnormally low clay content, and maintains a 
 very loose, open structure. 
 
 No. 16T4 represents a peculiar type of soil more or less scattered 
 over the islands, which upon absolute analysis shows about 20 per 
 cent of titanium oxid. It is high in iron and aluminum, and also 
 contains a larger percentage of ferrous iron than any of the soils 
 examined heretofore. It has a high specific gravity, bluish-gray 
 color, packs quite closely, has a " clayey silt" texture, and contains 
 an abnormally low content of moisture and organic matter. 
 
 No. 9 is a sample of the highly manganiferous type found in the 
 Wahiawa district on Oahu. It has a chocolate-brown color, a sandy 
 silt texture, and maintains an excellent mechanical condition, thus 
 permitting good aeration. 
 
 No. 292 represents the type of soil occurring in the lowlands in 
 and about Honolulu now being used for bananas, rice, and truck 
 farming. It has a sandy texture, grayish-brown color, and abnor- 
 mally high magnesia content. 
 
13 
 
 No. 290 is a peculiar type of soil occurring in the valley on the 
 experiment station grounds, and is undoubtedly of sedimentary 
 origin, its nature being largely determined by washings from the 
 mountain. It is a blue clay soil, exceedingly plastic when wet, but 
 upon drying forms hard compact lumps, and is somewhat similar to 
 adobe or gumbo soils. This soil also has a soapy feel, and during 
 the rainy season aeration and drainage are almost impossible. 
 
 Nos. 405 and 406 are samples of a silty soil, to be found in the 
 Kalihi district of Honolulu, which is being used for aquatic agricul- 
 ture, the former for rice, the latter for taro culture. 
 
 Nos. 416 and 417 represent the type of red clay soil which is so 
 abundant on all the islands. These samples were taken only a short 
 distance apart with the view in mind of determining the effect of 
 cultivation, 416 being a cultivated soil, while 417 is practically the 
 same soil from the unbroken sod. 
 
 Xo. 428 is a sample of highly organic, dark-colored soil from Glen- 
 wood, Olaa district, Hawaii. It has a very sandy texture and is 
 subjected to heavy rainfall and good drainage, but for some reason, 
 probably climatic, is unproductive. 
 
 No. 426 is a sample from Kealia, Kauai, and represents a brown 
 type of soil which has partly undergone a recementation of the par- 
 ticles into a yellow soft rock, hence the sample contains considerable 
 gravel. 
 
 No. 448 represents the type of yellow clay scattered throughout 
 the islands in certain districts, this sample having been taken from 
 near Hilo, Hawaii. 
 
 The relative solubility of the various constituents is shown sepa- 
 rately in order to bring out more clearly the effects of heat, one table 
 being devoted to each element. 
 
 silica. 
 
 The following table shows the results obtained in the study of the 
 effect of heating on the solubility of the silica: 
 
 Solubility of silica in water and fifth-normal nitric acid. 
 [Calculated on basis of dry soil.i 
 
 
 Soluble in water (parts per million). 
 
 Soluble in fifth-normal nitric acid (per 
 cent;. 
 
 Soil No. 
 
 Air dry. 
 
 Dried at 
 100° c. 
 
 Dried at 
 250° C 
 
 Ignited. 
 
 Air dry. 
 
 Dried at 
 100° c. 
 
 Dried at 
 250° C 
 
 Ignited. 
 
 74 
 
 35.3 
 10.0 
 
 4.2 
 2.2 
 2.3 
 
 12.5 
 2.4 
 4.0 
 
 15.9 
 1.15 
 0.0 
 
 13.0 
 2.0 
 9.5 
 8.3 
 2.1 
 6.9 
 7.8 
 
 10.5 
 4.5 
 
 14.9 
 3.38 
 0.0 
 
 8.7 
 3.0 
 8.5 
 7.2 
 
 17.2 
 5.7 
 7.8 
 9.4 
 
 31.2 
 8.9 
 7.9 
 0.0 
 
 8.7 
 
 4.0 
 
 7. 1 
 
 10.3 
 
 8.6 
 
 16.1 
 
 10.4 
 
 22.3 
 
 33.5 
 
 11.9 
 
 1.13 
 
 8.0 
 
 0. 196 
 .007 
 . . 15 
 .102 
 . 150 
 .180 
 . 005 
 .070 
 .165 
 .289 
 .024 
 .211 
 
 0.187 
 .006 
 .091 
 .680 
 .148 
 .219 
 .055 
 .076 
 .173 
 .261 
 .009 
 .226 
 
 0.113 
 .027 
 .084 
 
 .616 
 .264 
 .240 
 .077 
 .097 
 .301 
 .202 
 .062 
 .077 
 
 0.225 
 
 164 
 
 .067 
 
 9 
 
 .190 
 
 292 
 
 .523 
 
 290 
 
 .596 
 
 405 
 
 .267 
 
 416 
 
 .192 
 
 417 
 
 206 
 
 ttfl 
 
 428 
 
 426 
 
 .292 
 . 320 
 .158 
 .327 
 
14 
 
 The results of the silica determinations in the water extract are 
 rather inconsistent, but the average shows the highest solubility at 
 ignition. It will be observed that the data obtained with fifth-normal 
 nitric acid disclose some very interesting facts which show that an 
 increase in solubility of silica in dilute nitric acid in Hawaiian soils 
 is produced upon heating to ignition. Furthermore, the tendency 
 points toward a general increase in solubility with increase in tempera- 
 ture. Attention is called to the fact that the soils high in magnesia 
 show the greatest solubility of silica in dilute nitric acid. An excep- 
 tion in this particular is found in sample No. 164, a soil almost devoid 
 of organic matter and containing a very high titanium, iron, and 
 silica content. A further discussion of these results will be taken up 
 following the table of alumina determinations in consideration of the 
 relation of these two elements in the soil. 
 
 ALUMINA. 
 
 The following table shows the results obtained in the determinations 
 of alumina in heated and unheated soils: 
 
 Solubility of alumina in water and fifth-normal nitric acid. 
 [Calculated on basis of dry soil.] 
 
 ' 
 
 Soluble in water (parts per million). 
 
 Soluble in fifth normal nitric acid (per 
 cent). 
 
 Soil No. 
 
 Air dry. 
 
 Dried at 
 100° c. 
 
 Dried at 
 250° C 
 
 Ignited. 
 
 Air dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250° C 
 
 Ignited. 
 
 74 
 
 11.1 
 
 7.5 
 
 4.8 
 
 16.6 
 
 19.1 
 
 7.6 
 
 17.6 
 
 15.3 
 
 10.3 
 
 4.4 
 
 2.9 
 
 4.9 
 
 3.2 
 
 9.5 
 
 1.1 
 
 17.6 
 
 12.7 
 
 13.8 
 
 12.8 
 
 9.0 
 
 19.6 
 
 6.3 
 
 6.6 
 
 .7 
 
 10.3 
 
 9.5 
 
 9.5 
 
 14.5 
 
 12.8 
 
 17.6 
 
 16.1 
 
 4.8 
 
 28.5 
 
 11.9 
 
 1.7 
 
 5.8 
 
 22.3 
 
 5.0 
 
 3.7 
 
 17.1 
 
 17.7 
 
 12.2 
 
 20.9 
 
 28.9 
 
 38.0 
 
 8.8 
 
 2.1 
 
 2.6 
 
 0.291 
 .060 
 .583 
 .874 
 .266 
 .169 
 .420 
 .679 
 .295 
 
 2.261 
 .308 
 .979 
 
 0.292 
 .048 
 .675 
 .598 
 .292 
 .133 
 .509 
 .661 
 .314 
 
 2.031 
 .347 
 
 1.757 
 
 0.318 
 
 .139 
 
 .676 
 
 .584 
 
 .691 
 
 .444 
 
 1.057 
 
 1.413 
 
 .882 
 
 2.208 
 
 1.192 
 
 1.966 
 
 0.9.56 
 
 164... 
 
 .288 
 
 9 
 
 1.034 
 
 292 
 
 1.055 
 
 290... 
 
 .749 
 
 405 
 
 .897 
 
 416 
 
 1.515 
 
 417 
 
 1.495 
 
 406 
 
 1.425 
 
 428 
 
 2.244 
 
 426 
 
 1.571 
 
 448 
 
 2.757 
 
 
 
 It will be observed from this table that the alumina is affected in 
 very much the same way as the silica. The results, while somewhat 
 inconsistent, show an increase in water-soluble alumina in the heated 
 soils, the number showing increase of alumina by heating from 100 to 
 250° C, being about the same as in passing to ignition. The effect of 
 heat upon the solubility of this element in dilute nitric acid is very 
 marked and increases regularly with increase in temperature. There 
 is scarcely any correlation between the solubility of the alumina and 
 the total amount of silica present. However, it is worthy of note 
 that there seems to be a relation between the solubility of the alumina 
 in dilute nitric acid and the volatile matter (organic matter and 
 combined water) existing in the soil, as will be readily seen from the 
 
15 
 
 table. Soil No. 164 is almost devoid of organic matter and combined 
 water and contains the least soluble alumina, while, on the other 
 hand, those soils in which the volatile matter is highest contain the 
 most soluble alumina, this being especially noticeable in soils Nos. 
 428 and 448. 
 
 The effect of heat upon the solubility of alumina and silica, 
 especially in water, is probably referable to a number of causes. It 
 is believed, however, to be primarily physical, being related to an 
 alteration of the films surrounding the soil particles and to a modifica- 
 tion of the colloidal forms which these elements probably assume 
 under the prevailing conditions. The former effect will be discussed 
 in greater detail farther on. Dehydration and certain chemical 
 alterations at the higher temperatures would, on the other hand, 
 tend toward increasing the solubility in acids through the action of 
 heat upon the hydrated silicates. It has long been known that 
 certain aluminum silicates become more soluble in acids as a direct 
 effect of heat. In the early manufacture of alum advantage was 
 taken of this fact. 
 
 IRON. 
 
 The relative amounts of iron (Fe 2 3 ) recovered by the two solvents 
 appear in the following table: 
 
 Solubility of iron in water and fifth-normal nitric acid. 
 [Calculated on basis of dry soil.] 
 
 Soil No. 
 
 Soluble in water (parts per million). 
 
 Soluble in fifth-normal nitric acid (per 
 cent). 
 
 Air dry. 
 
 Dried at 
 100° c. 
 
 Dried at 
 250° C 
 
 Ignited. 
 
 Air dry. 
 
 Dried at 
 100° c. 
 
 Dried at 
 250° C. 
 
 Ignited. 
 
 74 
 
 17.6 
 3.5 
 3.7 
 2.9 
 4.8 
 6.4 
 2.8 
 5.2 
 4.6 
 1.9 
 1.7 
 2.1 
 
 9.7 
 3.5 
 5.3 
 5.3 
 3.2 
 9.2 
 2.8 
 2.7 
 2.7 
 2.7 
 1.3 
 3.2 
 
 9.2 
 3.5 
 3.9 
 3.1 
 4.4 
 5.4 
 2.8 
 3.3 
 4.0 
 3.2 
 1.6 
 2.3 
 
 12.5 
 5.1 
 4.5 
 3.5 
 1.8 
 5.1 
 2.5 
 3.8 
 2.1 
 1.6 
 1.3 
 2.1 
 
 0.003 
 .005 
 .007 
 .194 
 .069 
 .324 
 .032 
 .026 
 .515 
 .024 
 .037 
 .051 
 
 0.002 
 .007 
 .016 
 .037 
 .069 
 .302 
 .032 
 .029 
 .487 
 . 033 
 .061 
 .038 
 
 0.006 
 .083 
 .006 
 .037 
 .142 
 .290 
 .027 
 .029 
 .333 
 .039 
 .014 
 .077 
 
 0.055 
 
 164 
 
 .047 
 
 9 
 
 .006 
 
 292 
 
 .013 
 
 290 
 
 .046 
 
 405 
 
 .157 
 
 416 
 
 .015 
 
 417 
 
 .033 
 
 406 
 
 .158 
 
 428 
 
 .107 
 
 426.... 
 
 .082 
 
 448 
 
 .024 
 
 
 
 Again, there is considerable inconsistency in the results, but an 
 average shows the solubility of iron in water to be greatest in the 
 air-dried soil. The solubility in dilute nitric acid is much less con- 
 sistent than that in water, thereby making it impossible to advance 
 any conclusions except to call attention to the fact that the alumina 
 in Hawaiian soils is very much more soluble, both in water and in 
 dilute nitric acid, than is the iron. But if the results from samples 
 Xos. 292, 405, and 406 be disregarded, and this is plainly permissible 
 since these soils are used in aquatic agriculture and the major part 
 of the soluble iron is in the ferrous condition and would be oxidized 
 
16 
 
 to the ferric condition on being heated to higher temperatures, thus 
 becoming less soluble, then the figures show a marked increase in 
 solubility of the iron with increase in temperature. It will be noticed 
 that the three soils which it is proposed to disregard in drawing con- 
 clusions show a markedly regular decrease in solubility of the iron 
 from the air-dried to the ignition state. A qualitative test of the 
 water extract from these three soils showed a very high concentra- 
 tion of ferrous iron from the wet and air-dry samples. In several of 
 the samples in the series there is a close correlation between the effects 
 of the heat on iron and alumina, but it is by no means general. 
 
 Iron, alumina, and silica are apparently the constituents least solu- 
 ble in water. The greater solubility of iron in the air-dried soil may 
 be explained by the fact that the normal mechanical condition of 
 Hawaiian soils is conducive to reducing conditions which result in 
 the formation of small quantities of ferrous compounds. Hawaiian 
 soils, although characteristically basic, normally give an acid reac- 
 tion, due indirectly to the high clay content and its accompanying 
 poor aeration. Magnification of this condition is to be found in the 
 rice and taro soils, as will be shown in a later table (p. 24), in which 
 soluble iron is found in comparatively large amounts. In such cases 
 it is to be expected that the direct effect of heat would be to oxidize 
 the iron and thus render it less soluble. Further confirmation of 
 this theory is found in the cultivated and uncultivated soils (Nos. 
 416 and 417, respectively), in which the iron content of the latter is 
 shown to be the more soluble. After heating at 100° the solubility 
 in many instances is greater than in the air-dry samples and is prob- 
 ably due to physico-chemical effects upon the soil films and hydrated 
 silicates. These latter effects are also responsible for the increased 
 solubility of iron in dilute nitric acid as a result of heat. 
 
 MANGANESE. 
 
 The results obtained from the manganese (Mn 3 4 ) determinations 
 are shown in the following table : 
 
 Solubility of manganese in water and fifth-normal nitric acid. 
 [Calculated on basis of dry soil.] 
 
 
 Soluble in water (parts per 
 
 million). 
 
 Soluble in fifth-normal nitric 
 cent). 
 
 acid (per 
 
 Soil No. 
 
 Air dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250° C. 
 
 Ignited. 
 
 Air dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250° C. 
 
 Ignited. 
 
 74 
 
 26.5 
 9.0 
 
 23.5 
 5.2 
 
 29.4 
 5.9 
 2.2 
 
 15. 7 
 9.1 
 
 l.i. 9 
 6.9 
 2.8 
 
 30.4 
 11.0 
 
 26.5 
 
 4.1 
 20.4 
 10.3 
 
 4.5 
 £8.7 
 
 4.4 
 161.1 
 
 9.0 
 13.4 
 
 30.4 
 10.0 
 25.5 
 41.4 
 40.8 
 14.9 
 14.4 
 
 180.5 
 
 6.0 
 
 32.8 
 
 90.3 
 
 108.7 
 
 30.4 
 
 9.0 
 
 20.1 
 
 14.5 
 
 45.1 
 
 18.4 
 
 14.8 
 
 219.2 
 
 9.6 
 
 6.3 
 
 33.8 
 
 119.6 
 
 0.063 
 .003 
 .494 
 .070 
 .049 
 .062 
 .349 
 .385 
 .035 
 .094 
 .004 
 .028 
 
 0.041 
 .008 
 . 669 
 .098 
 .076 
 .062 
 .529 
 .580 
 .030 
 .102 
 .012 
 .032 
 
 0.217 
 .013 
 
 1.692 
 .106 
 .115 
 .047 
 
 1.314 
 
 1.052 
 .048 
 .225 
 040 
 .126 
 
 0.071 
 
 1C4 
 
 .006 
 
 9 
 
 1. 129 
 
 292 
 
 .067 
 
 290 
 
 .118 
 
 405 
 
 .041 
 
 416 
 
 .739 
 
 417 
 
 .748 
 
 406 
 
 .040 
 
 428 
 
 .135 
 
 426 
 
 .023 
 
 448 
 
 .050 
 
 
 
17 
 
 ' This table shows that the solubility .of manganese in water is much 
 greater in the heated soils/being most soluble in the ignited samples. 
 The surprising feature of this table is the fact that several of the soils 
 in the series show manganese in- a much more soluble form than the 
 manganiferous soil containing 9.21 per cent total Mn 3 4 . A possible 
 explanation is found in the results upon the cultivated and unculti- 
 vated soils (Nos. 416 and 417, respectively), namely, that cultivation 
 and the accompanying aeration has the effect of producing a lower 
 state of oxidation or other changes which render the manganese less 
 soluble in water. An observation of Nos. 416 and 417 (cultivated and 
 uncultivated) shows a large decrease in solubility as a result of culti- 
 vation, and the highly manganiferous soil (No. 9) has been in culti- 
 vation for some time. - 
 
 The table showing the solubility of manganese in dilute nitric acid 
 presents a remarkably consistent series of results, as is shown by the 
 increase in solubility as a result of the action of heat up to 250° C, 
 followed by a large decrease as effected by ignition. This is true with 
 only two exceptions in the entire series. 
 
 It is difficult to explain the effects of heat upon the solubility of 
 manganese. This element occurs in some Hawaiian soils as concre- 
 tions, especially in the highly manganiferous soils, and is present, at 
 least partially, as manganese dioxid. But in the normal types con- 
 cretions are absent, and here the manganese probably exists largely 
 in a lower state of oxidation, and hence in a more soluble form. In 
 any case manganites and salts may occur to a limited extent. As 
 already noted, the soils heated to 250° C. and ignition gave the more 
 concentrated water extract, an average indicating the maximum con- 
 centration from the ignited soils. The effect of heat upon the phys- 
 ical properties is probably the prime factor which influences the sol- 
 ubility in water. With one exception the oxids of manganese are 
 quite insoluble in nitric acid, this oxid being manganous oxid (MnO). 
 Therefore the higher oxids, such as manganomanganic oxid (Mn 3 4 ) 
 and manganic oxid (Mn 2 3 ) , which are both essentially combinations 
 of manganese dioxid and manganous oxid, 1 , are soluble in. nitric acid 
 to the extent of their MnO content, while their Mn0 2 content remains 
 insoluble. Consequently the solubility of manganese oxids increases 
 with increase in heat owing to the above-mentioned decrease in state 
 of oxidation, as high temperatures convert Mn0 2 into Mn 3 4 and 
 Mn 2 3 , each of which is partially soluble in nitric acid. Therefore 
 heat would tend to increase the solubility in nitric acid of that portion 
 occurring as Mn0 2 . 
 
 In addition, it is known that the action of heat upon organic com- 
 pounds of manganese and also certain of its salts converts them into 
 
 i MnjO<— 2 Mno+MnOj; Mn I 8 =MnO + MnOj. Hence it may be observed that MnjO« contains the 
 more soluble manganese. 
 
 14000°— Bull. 30—13 3 
 
18 
 
 oxids. Then, apparently the more soluble oxid, Mn 3 4 , is formed in 
 greater amounts when the soil is heated to 250° C. 
 
 LIME AND MAGNESIA. 
 
 The two tables below show the effects of heat upon the solubility 
 of lime and magnesia : 
 
 Solubility of lime in water and fifth-normal nitric acid. 
 [Calculated on basis of dry soiL] 
 
 Soil No. 
 
 Soluble in water (parts per million). 
 
 Soluble in fifth-normal nitric acid (per 
 
 cent). 
 
 Air dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250° C. 
 
 Ignited. 
 
 Air dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250° C. 
 
 Ignited. 
 
 74 
 
 176.8 
 
 28.1 
 
 224. 9 
 
 112.6 
 
 183.0 
 
 296.9 
 
 82.2 
 
 26.5 
 
 57.1 
 
 184.4 
 
 16.1 
 
 59.2 
 
 330.6 
 
 44.2 
 
 302.9 
 
 86.9 
 
 232.1 
 
 133.3 
 
 107.3 
 
 98.5 
 
 93.9 
 
 1, 455. 6 
 
 33.8 
 
 67.1 
 
 2,801.1 
 64.3 
 910.9 
 242.3 
 195.6 
 363.0 
 270.6 
 330.5 
 697.5 
 
 1,509.3 
 225.8 
 763.6 
 
 1,039.5 
 38.1 
 766.8 
 207.1 
 206.3 
 261.9 
 232.6 
 332. 9 
 547.7 
 220.6 
 106.1 
 708.6 
 
 2.312 
 .026 
 .448 
 .147 
 .378 
 .344 
 .159 
 .174 
 .388 
 .466 
 .056 
 .248 
 
 2.332 
 .030 
 .909 
 .856 
 .406 
 .362 
 .158 
 .174 
 .409 
 .479 
 .083 
 .252 
 
 2.131 
 
 .024 
 .511 
 .986 
 .318 
 .330 
 .124 
 .167 
 .329 
 .395 
 .056 
 .226 
 
 1.427 
 .024 
 .323 
 .674 
 .876 
 .316 
 .108 
 .136 
 .191 
 .368 
 .058 
 .162 
 
 L64 
 
 9 
 
 292 
 
 290 
 
 405 
 
 416 
 
 417 
 
 406 
 
 428 
 
 426 
 
 448 
 
 
 Solubility of magnesia in water and fifth-normal nitric acid. 
 [Calculated on basis of dry soil.] 
 
 Soil No. 
 
 Soluble in water (parts per 
 
 million). 
 
 Soluble in fifth-normal nitric acid (per 
 cent). 
 
 Air dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250° C 
 
 Ignited. 
 
 Air dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250° C. 
 
 Ignited. 
 
 74 
 
 75.1 
 
 50.2 
 
 96.4 
 
 83.4 
 
 285.2 
 
 209.7 
 
 105.1 
 
 67.5 
 
 82.2 
 
 152.6 
 
 34.6 
 
 57.8 
 
 73.9 
 
 42.2 
 
 99.5 
 
 91.1 
 
 385.2 
 
 130.9 
 
 127.5 
 
 126.6 
 
 87.2 
 
 366.8 
 
 47.4 
 
 77.8 
 
 182.7 
 60.2 
 167.3 
 136.7 
 230.3 
 151.6 
 140.9 
 189.8 
 234.7 
 268.4 
 158.1 
 297.9 
 
 63.1 
 
 44.2 
 150.4 
 130.5 
 192.6 
 147.0 
 127.5 
 157.1 
 245.9 
 134.2 
 108.4 
 303.3 
 
 0.121 
 .019 
 .071 
 .150 
 .500 
 .206 
 .073 
 .071 
 .204 
 .114 
 .047 
 .074 
 
 0.123 
 .020 
 .066 
 .359 
 .522 
 .204 
 .062 
 .073 
 .226 
 .107 
 .040 
 .064 
 
 0.138 
 .021 
 .081 
 .344 
 .301 
 .140 
 .042 
 .049 
 .115 
 .082 
 .041 
 .048 
 
 0.096 
 
 164 
 
 .019 
 
 3 
 
 .049 
 
 292 
 
 .197 
 
 290 
 
 .283 
 
 405 
 
 .060 
 
 416 
 
 .046 
 
 417 
 
 .062 
 
 406 
 
 .098 
 
 428 
 
 .079 
 
 426 
 
 .044 
 
 448 
 
 .048 
 
 
 
 The series of lime determinations shows that this constituent is 
 most soluble in water in the soils which were heated to 250° C. 
 and least soluble in the air-dried soils. This is true of every sample 
 except one (No. 290), this latter being a peculiar adobe type of 
 soil from the experiment station grounds. In dilute nitric acid it 
 will be observed that lime is most soluble in those soils heated to 
 100° C, and, unlike the water extractions, the least concentration 
 is obtained from the ignited soils. Thus it is shown that the action 
 of nitric acid in no way correlates with that of distilled water. How- 
 ever, the results show the more highly organic soil to contain lime 
 
19 
 
 in such form as to be more soluble in weak solvents, No. 164, a 
 mineral soil, being the least soluble. Attention is also called to 
 the effect of cultivation or aeration upon the solubility of lime and 
 magnesia, namely, that the cultivated soils contain these elements 
 in far more soluble form. 
 
 From a study of the table of magnesia determinations it is evi- 
 dent that the action of the solvents upon this element is quite sim- 
 ilar to their action on lime as regards the effects of heat, but that 
 the lime is very much the more soluble both in water and in dilute 
 nitric acid. The results of the extractions with water show a max- 
 imum solubility in the samples heated to 250° C, the least soluble 
 magnesia in the air-dry samples. This exactly correlates with the 
 results of the lime determination. The solubility in dilute nitric acid 
 does not correspond so closely, but the general tendency is similar 
 in that the air-dry samples and those dried at 100° C. contain this 
 element in the highest state of solubility, while in the ignited soils 
 it is least soluble. An important fact to which attention is called 
 is that, although most of the soils in this series show from digestion 
 with hydrochloric acid (1.115 specific gravity) a higher magnesia con- 
 tent than lime, one of them four times as much, yet the lime, with 
 very few exceptions, is considerably more soluble. One exception 
 is to be found in sample No. 290, which represents a soil having a 
 characteristic soapy property indicating the presence of hydrous 
 magnesium silicate. 
 
 The effect of heat on the solubility of lime and magnesia is more 
 striking than in case of the other elements. It is highly probable that 
 the increased concentration of the water extract of the soil heated to 
 100° C. over the air-dried sample is produced through physical causes, 
 namely, destruction of the soil film and delrydration accompanied by 
 a slight decomposition of organic matter. On the other hand, the soil 
 when heated to 250° C. undergoes more completely all the above trans- 
 formations as well as decomposition of organic matter. Since calcium 
 and magnesium are two of the elements universally combined with 
 organic matter, there necessarily follows an increase in solubility as 
 a result of the more complete decomposition. The soils showing the 
 greatest solubility of these elements in water were those containing 
 the highest organic matter. 
 
 The decrease in solubility of lime and magnesia in water and in 
 nitric acid at 250° C. and ignition is hard to explain. It is undoubt- 
 edly partly due to chemical changes in the soluble forms resulting 
 from the decomposition of the organic matter and is also influenced 
 by the decrease in exposed surfaces as a result of an aggregation of the 
 soil particles and probably other physical factors. It is suggested 
 that one of the chemical changes taking place as a result of heat is 
 that of a replacement of the potash and soda in the silicates by 
 
20 
 
 magnesia and lime, more particularly the latter. The data in the 
 tables show a decrease in solubility of lime and an increase in that of 
 potash upon ignition in a majority of the samples. In addition to the 
 above-mentioned factors a decrease in solubility after ignition would 
 be produced by the conversion of the bicarbonates into normal car- 
 bonates, the former of which are more soluble than the latter. This 
 would, of course, be most striking in the water extracts. 
 
 POTASH. 
 
 ' The following table shows the relative effects of heat upon the solu- 
 bility of potash: 
 
 Solubifity of potash in water and fifth-normal nitric acid. 
 Calculated on basis of dry soil.] 
 
 Soil No. 
 
 Soluble in water (parts per 
 
 million). 
 
 Soluble . in fifth-normal nitric acid (per 
 cent). 
 
 Air dry. 
 
 Dried at 
 100° c. 
 
 Dried at 
 250° C. 
 
 Ignited. 
 
 Air dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250° C 
 
 Ignited. ; 
 
 74 
 
 128.2 
 64.3 
 
 117.8 
 77.2 
 87.1 
 96.6 
 
 "98.2 
 60.3 
 36.5 
 
 £44.8 
 43.8 
 
 119.8 
 
 117.4 
 
 82.3 
 
 192.7 
 76.3 
 92.4 
 55.1 
 96.2 
 
 100.8 
 49.2 
 
 202.8 
 58.7 
 
 107.4 
 
 339.3 
 40.1 
 
 301.9 
 
 118.0 
 90.6 
 45.9 
 78.3 
 77.4 
 19.4' 
 
 353.5 
 56.4 
 64.4 
 
 217.5 
 
 132.5 
 
 260.6 
 
 • 83.8 
 
 .77.4 
 
 43.6 
 
 147.6 
 
 140,6 
 
 . 78.2 
 
 220.7 
 
 182.9 
 
 59.0 
 
 0.053 
 .027 
 .073 
 .061 
 .177 
 . 056 . 
 .055 
 
 • .061 
 .014 
 .0:38 
 .025 
 .032 
 
 0.066 
 '.032 
 .081 
 . 155 
 .142 
 .084 
 .056 
 .0,54 
 .013 
 .051 
 .024 
 .032 
 
 0.050 
 .026 
 .064 
 .202 
 .054 
 .095 
 .038 
 .038 
 .032 
 .029 
 .030 
 .033 
 
 0.068 
 
 i 4 
 
 .071 
 
 
 .113 
 
 
 
 |92 
 
 .134 
 
 290 . . .' 
 
 .094 
 
 405 
 
 .090 
 
 416 
 
 .062 
 
 417 ' 
 
 .072 
 
 406 
 
 .022 
 
 428 
 
 .041 
 
 426 
 
 .070 
 
 448 
 
 .053 
 
 
 
 . The figures ■show that the effect of heat upon potash is slightly 
 different from -the effects on lime and magnesia. The ignited soils 
 appear to contain this element in the most soluble form, while the 
 samples dried in air and at 100° C. contain it in the least soluble 
 form. In the air-dried samples potash is also more soluble in the 
 cultivated than in the uncultivated soil, and the greatest solubility 
 of this element is also found in the highly organic soils. 
 
 Soils in general possess fixing power for potash and for phos- 
 phoric acid in particular. The fixing of potash is generally believed 
 to be due to hydrated silicates and organic matter. Cameron and 
 Bell 1 on continuously extracting a soil with water until no more 
 potash dissolved, then grinding the sample and reextracting, found 
 an additional amount of potash to be removed. This they attributed 
 to a colloidal aluminum silicate upon the surface of the particles, 
 thus protecting them from the action of the water as well as absorb- 
 ing the potash. Dehydration and decomposition would therefore 
 materially overcome the fixing power, and the potash replaced by 
 lime or magnesia would not be refixed during a short period. 
 
 ' U. S. Dept. Agr., Bur. Soils Bui. 30, p. 26. 
 
21 
 
 • PHOSPHORIC ACID. 
 
 i In the next table are shown the results of the action of heat on the 
 Solubility of phosphoric acid.- 
 
 Solubility of phosphoric acid in water and fifth-normal nitric acid. 
 iCalculated on basis of dry soil.] 
 
 Soil No. 
 
 Soluble in water (parts per 
 
 million). 
 
 Soluble in fifth-normal nitric acid (per 
 cent). 
 
 Air dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250° C. 
 
 Ignited. 
 
 Air dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250* C 
 
 Ignited. 
 
 7-1 
 
 264 
 
 g 
 
 39.8 
 
 24.1 
 
 17.1 
 
 21.9 
 
 22.9 
 
 27.1 
 
 36.5 
 
 54.3' 
 
 23.4 
 
 2.5.6 
 
 25.4 
 
 29.6 
 
 69.6 
 36.1 
 44.5 
 26.9 
 36.5 
 31.0 
 43.6 
 52.7 
 35.7 
 38.7 
 24.8 
 36.2 
 
 58.7 
 16.1 
 52.9 
 23.8 
 25.8 
 33.0 
 49.2 
 46.8 
 21.2 
 26.8 
 27.1 
 37.6 
 
 32.6 
 15.1 
 32.8 
 22.8 
 27.9 
 25.3 
 51.4 
 39.8 
 23.4 
 23.8 
 27.1 
 28.1 
 
 0.007 
 .005 
 .007 
 .058 
 .006 
 .011 
 .005 
 .005 
 .024 
 .011 
 .008 
 .028 
 
 0.008 
 .006 
 .007 
 .018 
 .016 
 .014 
 .007 
 .008 
 .030 
 .013 
 .012 
 
 • .028 
 
 0.024 
 .007 
 .011 
 .020 
 .020 
 
 -.027 
 .007 
 .009 
 .064 
 .012 
 .011 
 .036 
 
 0.043 
 
 .00'J 
 .013 
 
 2D2 
 
 290 
 
 40.5 
 
 416 
 
 417 
 
 .053 
 .031 
 .021 
 .006 
 .005 
 
 406 
 
 .047 
 
 428 
 
 .014 
 
 426 
 
 .013 
 
 44S 
 
 .020 
 
 
 
 It may be seen from this table that the solubility of phosphoric 
 acid is materially affected by heat, the solubility in water being 
 greatest in the soils heated to 100° and 250° C, if it be permissible 
 to draw conclusions from the general averages, while it is least soluble 
 in the air-dried soils. It is also worthy of note that this element is 
 more soluble in the uncultivated than the cultivated soil, the former, 
 however, decreasing with increase in heat. In the extractions made 
 with dilute nitric acid the average indicates a greater solubility in 
 the ignited soils, the solubility tending to increase with increase in 
 temperature. 
 
 Phosphoric acid exists in soils in major part combined with iron, 
 aluminum, magnesium, and calcium, and is also found combined with 
 organic matter, being always present in the so-called humus of soils. 
 It may be in the form of basic phosphates, hydrogen phosphates, or as 
 complex phosphates in combination with more than one element. 
 It is probably combined mostly with iron and aluminum and titanium 
 in Hawaiian soils. Considerable work has been done upon the effect 
 of heat upon the solubility of this constituent and several attempts 
 have been made to draw conclusions from these results as to its state 
 of combination; that is, whether organically or inorganically com- 
 bined. Peterson ■ using fifth-normal nitric acid found that after 
 oxidizing the organic matter with hydrogen peroxid there was no 
 increase in the solubility of phosphoric acid when the soil was heated 
 to 240° C. He concluded, therefore, that the solubility of mineral 
 phosphates in soils is not increased up to 240° C. The author's results 
 tend to indicate a decrease in solubility of phosphoric acid at high tem- 
 
 ' Wisconsin Sta. Research Bui. 19 
 
22 
 
 peratures, due either to a chemical change in its combination to a form 
 less soluble in water or an increase in the absorbing power of the soil. 
 The increase effected at 100° and 250° C. is undoubtedly partly due to 
 destruction of organic matter and to the breaking up of the colloidal 
 film. The action of dilute nitric acid is somewhat different, in that 
 an increase in solubility upon ignition accompanies that of iron, 
 alumina, silica, and titanium. Iron and aluminum in Hawaiian soils 
 occur in the form of hydrates to a certain extent and are more or less 
 impregnated with the phosphoric acid and titanium oxid, not only 
 holding them in chemical combination, but also mechanically. The 
 effect of heat would directly increase the solubility of these con- 
 stituents in dilute nitric acid gradually up to the point of ignition, 
 at which point the decomposition of the hydrates would be at a 
 maximum. Changes due to the destruction of organic matter would 
 cause an increase in the solubility of this element. Another factor 
 of some importance in this connection is that of precipitation subse- 
 quent to solution. The increased solubility of aluminum and man- 
 ganese would probably produce some precipitation of phosphoric 
 acid, particularly in the water extract. 
 
 SULPHATES. 
 
 The following table shows the solubility of sulphates (S0 3 ) as 
 affected by heat: 
 
 Solubility of sulphuric acid in water and fifth-normal nitric 
 [Calculated on basis of dry soil.| 
 
 acid. 
 
 
 Soil No. 
 
 Soluble 
 
 n water (parts per million). 
 
 Soluble in fifth-normal nitric acid (per 
 cent). 
 
 Air dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250° C. 
 
 Ignited. 
 
 Aix dry. 
 
 Dried at 
 100° C. 
 
 Dried at 
 250° C. 
 
 Ignited. 
 
 74 
 
 172.4 
 72.3 
 111.4 
 
 164.7 
 
 100. 2 
 
 129. 6 
 
 59.4 
 
 98.9 
 
 2C.0. 3 
 
 494.8 
 
 46.2 
 
 110.0 
 
 130.5 
 
 66.2 
 146.2 
 159.5 
 176.2 
 149.3 
 100.6 
 103.1 
 326.4 
 2, 123. 7 
 54.2 
 107.4 
 
 1,961.6 
 206.7 
 
 1,339.7 
 722.5 
 
 1,128.3 
 942.0 
 702.3 
 872.1 
 
 1,555.9 
 
 2, 598. 
 119.7 
 
 1,621.3 
 
 1,309.2 
 168.6 
 
 1,294.4 
 532.3 
 799.5 
 583.6 
 664.3 
 926.0 
 
 1, 479. 9 
 680.1 
 241.6 
 
 1,575.7 
 
 0.027 
 .037 
 .017 
 .067 
 .022 
 .018 
 .028 
 .032 
 .061 
 .089 
 .018 
 .028 
 
 0.019 
 .031 
 .019 
 .018 
 .026 
 .016 
 .035 
 .032 
 .086 
 .073 
 .034 
 .029 
 
 0.106 
 .027 
 .053 
 .019 
 .062 
 .067 
 .038 
 .037 
 .163 
 .101 
 .019 
 .044 
 
 0.067 
 
 164 
 
 .025 
 
 9 
 
 .034 
 
 292 
 
 .055 
 
 290 
 
 .063 
 
 405 
 
 .048 
 
 416 
 
 .041 
 
 417 
 
 .052 
 
 406 
 
 .187 
 
 428 
 
 .177 
 
 426 
 
 .024 
 
 448 
 
 .122 
 
 
 
 It will be seen from this table that the effect of heat upon the solu- 
 bility of the sulphates is quite marked, more so in the water extracts. 
 In this series the air-dried soil is the least soluble, that dried at 100° C* 
 next, while the maximum solubility is reached at about 250° C, de- 
 creasing upon ignition. On the other hand, the solubility in dilute 
 nitric acid is slightly different in that the average shows the maximum 
 solubility to be obtained from the ignited samples, the least soluble 
 being in the oven-dried (100° C.) soil. The surprising feature of these 
 results is the markedly greater solubility of sulphates in water than in 
 
23 
 
 nitric acid as shown in a number of instances, This is probably due 
 to precipitation subsequent to extraction in the nitric acid extracts. 
 Part of the increase in the solubility of sulphates in the heated 
 soils of this series was probably due to absorption of the products of 
 combustion of the gas used in heating the oven. It was found that 
 by passing the products of combustion through water a precipitate 
 of barium sulphate was obtainable upon the addition of barium 
 chlorid. King 1 found an enormous increase in the solubility of 
 sulphates upon heating in an oven at 110° C. using both gasoline and 
 kerosene as a source of heat, thus largely eliminating this factor. 
 In spite of the possibility of an introduction of error due to this 
 cause it is probable that the results tabulated here disclose correctly 
 the effect of heat upon the sulphates. In addition to the already- 
 mentioned reasons, namely, destruction of organic matter, soil films, 
 etc., it is necessary to take into consideration the chemical effect of 
 heat upon the various mineral sulphur compounds. Calcium sulphate 
 is known to exist in four forms, two being anhydrous, one of which is 
 more soluble than the other. Sulphur also exists in soils as sulphids 
 generally combined with iron, or as sulphates in combination with iron, 
 lime, or magnesia, also combined with organic matter in many essential 
 forms. The effect of heat would be most marked upon the latter in 
 that it would undergo considerable decomposition at 250°, the sulphur 
 being oxidized to sulphur dioxid or trioxid, which upon treatment 
 with water as a solvent would tend to form sulphuric acid or sulphates 
 to the extent of the bases in solution. On the other hand, it is evident 
 that large amounts of sulphur will be lost through volatilization upon 
 ignition. Soil Xo. 428, a highly organic soil, illustrates this effect 
 best in that the increase from air dried to oven dried (100° C.) is 
 1,600 parts per million, while the decrease from the sample heated 
 from 250° C. to ignition is 1,900 parts per million. It is evident 
 from these data that upon igniting the soils the sulphur set free from 
 the destruction of the organic matter is oxidized and volatilized so 
 that it is lost before combination with the bases takes place. 
 
 BICARBONATES. 
 
 The following table shows the bicarbonate content of the water 
 
 extracts : 
 
 Solubility of bicarbonates in water. 
 
 (Parts per million of dry soil.) 
 
 Treatment of soil. 
 
 Soil 
 No. 
 74. 
 
 Soil 
 No. 
 164. 
 
 Soil 
 No. 
 9. 
 
 Soil 
 No. 
 292. 
 
 Soil 
 No. 
 290. 
 
 Soil 
 No. 
 405. 
 
 Soil 
 No. 
 416. 
 
 Soil 
 No. 
 417. 
 
 Soil 
 No. 
 
 406. 
 
 Soil 
 No. 
 428. 
 
 SoU 
 No. 
 426. 
 
 
 370.1 
 
 44S.O 
 
 1,309.2 
 
 314.2 
 
 106.4 
 137.4 
 91.3 
 45.1 
 
 113.5 
 419.4 
 338.9 
 230.9 
 
 158.5 
 283.7 
 363.5 
 252.1 
 
 132.9 
 
 202.7 
 
 327.7 
 
 70.9 
 
 161.4 
 297.5 
 157.3 
 174.6 
 
 35.4 
 221.4 
 1533 
 
 73.8 
 
 73.6 
 2X6.0 
 143.0 
 
 53.9 
 
 52.5 
 136.4 
 
 68.2 
 118.5 
 
 73.1 
 204.3 
 582.8 
 133. 1 
 
 70.5 
 
 Dried at 100° C 
 
 Dried at 2.'*)° C 
 
 Ignited 
 
 102.7 
 SflS. 4 
 MD.fi 
 
 (7. S. Dopt. Iff., Bur. SoiLs Bui. 26 p. 56 
 
24 
 
 The results herewith shown are not very consistent, but the average 
 ndicates the maximum solubility of carbonic acid to be in the samples 
 treated to 100° and 250° C, indicating that drying has the effect of 
 increasing the amounts of bicarbonates in the soil and thus increasing 
 the solubility of the bases with which carbonic acid combines. One' 
 reason suggested in the above table for a decrease in water soluble 
 constituents upon ignition is that ignition would cause a transforma- 
 tion of the bicarbonates into normal carbonates, therefore temporarily 
 reducing their solubility in water. 
 
 At the beginning of this work . some determinations of titanium 
 were made, but these were not carried through the series. This 
 element was not present in the water extract in large enough quantities 
 to be determined. In the dilute nitric acid extracts it was present in 
 very small amounts in the samples dried, in air and at 100° C, but in 
 much larger quantities in the extracts from samples heated to 250° C. 
 and ignition, the maximum solubility being obtained upon the ignited, 
 samples. 
 
 EFFECT OF HEAT UPON RICE AND TARO SOILS. 
 
 In the following table is shown the effect of heat upon the soils used 
 in aquatic agriculture, comparing this with the solubility of the 
 elements in the wet and soggy condition: 
 
 
 Effect of heat upon soils used in aquatic agriculture. 
 [Parts per million of dry soil water extract.] 
 
 
 
 Condition of 
 sample. 
 
 Silica 
 (Si0 2 ). 
 
 Alu- 
 mina 
 
 (A1 2 3 ). 
 
 Iron 
 
 oxid 
 
 (Fe 2 3 ). 
 
 Manga- 
 nese 
 oxid 
 
 (Mn 3 0<). 
 
 Lime 
 (CaO). 
 
 Mag- 
 nesia 
 (MgO). 
 
 Potash 
 
 (K 2 0). 
 
 Phos- 
 phoric 
 acid 
 (P2O5). 
 
 Sul- 
 phuric 
 
 acid 
 (S0 3 ). 
 
 Bicar- 
 bonates 
 (HCO3). 
 
 Rice soil, No. 405: 
 Wet 
 
 6.9 
 2.3 
 
 .6.9 
 
 5.7 
 16.1 
 
 36.6 
 4.6 
 
 4.5 
 
 31.2 
 33.5 
 
 5.6 
 7.6 
 
 13.8 
 
 17.6 
 12.2 
 
 62.4 
 10.3 
 
 19.6 
 
 28.5 
 38.0 
 
 12.2 
 6.4 
 
 9.2 
 
 ■ 5.4 
 5.1 
 
 86.1 
 4.6 
 
 2.7 
 
 4.0 
 2.1 
 
 64.7 
 5.9 
 
 10.3 
 
 14.9 
 18.4 
 
 34.4 
 9.1 
 
 4.4 
 
 6.0 
 9.6 
 
 664.8 
 296.9 
 
 133.3 
 
 363.0 
 261.9 
 
 318.6 
 57.1 
 
 93.9 
 
 697.5 
 547.7 
 
 458.7 
 209.7 
 
 130.9 
 
 151.6 
 147.0 
 
 310.0 
 82.2 
 
 87.2 
 
 234.7 
 245.9 
 
 111.9 
 96.6 
 
 55.1 
 
 45.9 
 43.6 
 
 31.8 
 36.5 
 
 49.2 
 
 19.4 
 
 78.2 
 
 43.7 
 27.1 
 
 31.0 
 
 33.0 
 25.3 
 
 38.7 
 23.4 
 
 35.7 
 
 21.2 
 23.4 
 
 153.9 
 129.6 
 
 149.3 
 
 942.0 
 583.6 
 
 137.8 
 260.3 
 
 326.4 
 
 1,555.9 
 1,479.9 
 
 328 9 
 
 Air dry 
 
 Dried at 100° 
 c 
 
 161.4 
 297.5 
 
 Dried at 250° 
 c 
 
 157.3 
 
 Ignited 
 
 Tarosoil,No. 406: 
 Wet 
 
 174.6 
 294.9 
 
 Air dry 
 
 Dried at 100° 
 c 
 
 52.5 
 136.4 
 
 Dried at 250° 
 c 
 
 68.2 
 
 Ignited 
 
 118.5 
 
 When the types of soil were chosen for use in this series, two were 
 selected with a view to obtaining some information upon the soils 
 in use for rice and taro culture. It would be expected that heat and 
 its accompanying oxidation would have a marked effect upon this 
 type of soil for the reason that for the most part it exists in a reduc- 
 ing environment. The above table shows solubility in water only. 
 The samples were taken from the field in wet condition and extrac- 
 tions were made upon weighed samples immediately upon receipt 
 in the laboratory, the moisture content in this state being about 
 
25 
 
 50 per cent. This table discloses the high concentration of soluble 
 plant food in these soils under the reducing conditions. While the 
 mineral constituents tend to increase in solubility with increase in 
 heat with relation to the air-dry samples, a maximum solubility is 
 obtained from the wet samples in the case of the iron, manganese, 
 lime, magnesia, phosphoric acid, and bicarbonates, and in one of 
 the samples a maximum solubility is obtained for the remaining 
 constituents, silica, alumina, and potash. Therefore, these results 
 indicate that the effect of drying and heating the soils used in aquatic 
 agriculture does not increase the solubility of the mineral constitu- 
 ents over and above the solubility in the wet state but rather brings 
 about a decrease in all constituents except sulphates. 
 
 The concentration of the extracts from these soils in the wet state 
 does not necessarily indicate that the mineral constituents, with the 
 exception of iron, are actually more soluble than those of dry-land 
 soils. Neither should we conclude that the abnormal concentra- 
 tion is wholly due to more complete diffusion coupled with greater 
 solubility induced by the environment to which these soils are sub- 
 jected. The amount of water always present in these soils is far in 
 excess of that occurring in dry-land soils, and since there necessarily 
 must be a tendency toward constancy in concentration regardless 
 of the amount of solvent present, in time the absolute amounts of 
 solids going into solution would be considerably greater in submerged 
 •soils. The moisture content of these two soils when received at the 
 laboratory was about 50 per cent, whereas the dry-land soils contain 
 very much less moisture. The water extracts obtained by the 
 methods employed, therefore, would necessarily contain greater 
 absolute amounts of substances already in solution in the soil water. 
 Hence the concentration of the nutrient solution occurring in sub- 
 merged soils need not necessarily be greater than that of dry-land 
 soils. 
 
 DISCUSSION. 
 
 The foregoing results show that an increase in solubility of the 
 mineral constituents of various types of Hawaiian soils is effected 
 by heating. The samples represent most of the normal and abnormal 
 types of the islands. That there are both chemical and physical 
 factors concerned in the phenomena at hand must be admitted at 
 the outset. It is believed, however, that the most important set 
 of factors affecting the solubility of inorganic soil constituents are 
 of a physical nature. 
 
 Undoubtedly the means by which the physical factors act is through 
 the soil moisture in its relation to the physical properties of the soil. 
 The conditions conducive to the formation of a colloidal state and the 
 subsequent relation of heat to the destruction of this colloid are two 
 of the most important of these factors. 
 
26 
 
 It is certain that soil moisture distributes itself around the soil 
 particles and in some instances as an impregnation within the par- 
 ticles. The moisture therefore occurs as thin films which, according 
 to certain physical conceptions, must be held around the particle by 
 an enormous pressure. From purely physical considerations this 
 pressure has been estimated at several thousand atmospheres. Under 
 such pressure the concentration of film water with reference to the 
 mineral matter should be much greater than that of the free or 
 capillary water in the soil. 
 
 Then the air-dried soil, the particles of which are still surrounded 
 by a film of moisture, when shaken with water, should theoretically 
 show the least solubility. The results reported in this bulletin in 
 most instances are in harmony with this assumption. But if the soil 
 be allowed to remain in the condition and environment prevailing in 
 submerged cultures, that is, in the presence of a large excess of water, 
 then in time diffusion would bring about a more or less equal distribu- 
 tion of dissolved materials throughout the entire water present and 
 the pressure of soil films would be decreased to a minimum or entirely 
 eliminated. Hence the amount of materials going into solution in 
 the free water in such soils would be expected to be abnormally high. 
 Upon air drying such soils the normal films would again appear with 
 a resulting decrease in solubility. Subsequent heating ought then 
 to affect these soils in a way similar to that produced on dry-land 
 soils. The data presented in the previous tables are again in harmony 
 with this view. 
 
 Water, however, not only exercises a solvent action on minerals 
 but forms various hydrates, the solubility and physical character of 
 which in some instances are greatly altered ; organic as well as inor- 
 ganic matter goes into solution with the result that the moisture films 
 around the particles became solution films, holding in suspension and 
 more or less intermingled with colloids, both organic and inorganic. 
 The films then may be looked upon as being of a colloidal nature. 1 
 
 Upon heating to 100° C. alterations in the films would take place 
 through evaporation and by partial dehydration of colloids, thus de- 
 stroying the pressure by which the film was previously held around 
 the particles. At the temperature of 100° C. the concentration of the 
 soil moisture would also be temporarily increased, due to increase in 
 solubility with heat. During the course of the evaporation the con- 
 centration of the soil moisture would increase to the saturation point, 
 after which the mineral matter would be deposited on the surface of 
 the film as evaporation went on. 2 Also the materials held in solution 
 in the interior of the permeable particles would be partially deposited 
 
 i No claim is made for originality in this view. The idea of soil films, colloidal films, etc., has been made 
 use of by various writers on soils. 
 * King (loc. cit.) in discussing the relative solubilities of fresh and dried soils advanced this idea. 
 

 27 
 
 on the surface of the water evaporated. Upon adding water to the 
 soil after having been dried, it is probable the materials deposited 
 from previous evaporation would be more soluble than the other 
 mineral constituents. In addition a certain amount of oxidation 
 and other chemical changes in the organic matter might reasonably 
 be expected to take place, which would have some effect on the 
 solubility oi the mineral bases that tend to combine with the organic 
 matter. 
 
 The solution obtained upon shaking with water a soil previously 
 dried should, in the light of these views, be of a greater concentration 
 than that prepared from the air-dried soil. With the absence of soil 
 films and a more or less altered condition of the colloids present the 
 solvent would have more ready access to the soil particles during a 
 short period in addition to coming into immediate contact with 
 solids deposited on the surface of the particles. 
 
 Why several of the mineral constituents of the soil should be so 
 markedly more soluble when heated to 250° C. than at the other 
 temperatures is a question not easily answered. The difference in 
 physical effects were quite noticeable in that there was a greater 
 aggregation of particles. Again, there was a more complete destruc- 
 tion of organic matter effected at this temperature, and also it is not 
 entirely impossible that drying at 100° C. for eight hours does not 
 effect a complete elimination of the soil moisture and especially the 
 water of chemical combination. It seems reasonable, then, that the 
 effects of heating to 100° C. are simply magnified when heated to 
 250° C. Added to this there is a more complete destruction of organic 
 matter, the effect, both physical and chemical, being of the same 
 general nature but more complete at the higher temperature. The 
 destruction of organic constituents being more complete would neces- 
 sarily increase the solubility of the mineral matter held in combination, 
 as it is generally conceded that the organic constituents of the soil 
 in its natural state are quite insoluble in water and acids, more 
 especially in the former. There is also evidence of the existence of 
 fatty or resinous organic matter which would materially affect the 
 properties of the soil film. For the decomposition of such bodies it 
 would be necessary to heat the soils considerably above 100° C. 
 
 In addition to the above-mentioned effects of heat the relation 
 between solid and solvent would naturally be affected by other factors. 
 Among these is the absorption or "fixing power" of the soil. 1 It is 
 reasonable to expect soils with widely varying physical and chemical 
 properties, such as those used in this series, to differ greatly in 
 absorptive power. Hence it is not at all unlikely that the lack of 
 consistency in some of the results in the foregoing tables is due 
 primarily to this factor. Not only is there lack of uniformity in 
 
 i Richter (Landw. Vers. Stat., 47 (1896), p. 269) found that heating increased the absorptive power oi 
 the soil for water. 
 
28 
 
 the absorptive power of soils, but they also show considerable selective 
 power in the absorption of mineral constituents. Soils high in 
 humus have a high fixing power, due to the ability of humus to 
 combine chemically with minerals, as well as its power of absorption, 
 and therefore the effect of heat upon highly organic soils should tend 
 to increase the solubility of the minerals. An example of this is given 
 in the cases of soils Nos. 74 and 428. Another factor is that of 
 precipitation following extraction, being the more marked in the 
 acid extract due to a more complete extraction. 
 
 In passing from 250° C. to ignition the effects are apparently of a 
 specific rather than general nature, as has been already indicated. 
 Among these effects are the volatilization of certain sulphur com- 
 pounds, conversion of bicarbonates into normal carbonates, de- 
 hydration of silicates, etc., replacing of potash by lime, and other 
 chemical transformations. In addition there is produced a greater 
 aggregation of the soil particles, resulting in a decrease in surface 
 area exposed to the solvent and an accompanying change in the 
 fixing and absorbing powers of the soil. It is possible, by application 
 of these conceptions, to explain the majority of changes, both increase 
 and decrease in solubility, resulting from ignition. 
 
 THE EFFECTS OF HEAT ON SOIL NITROGEN. 
 INTRODUCTION. 
 
 The data presented in the preceding pages indicate the existence 
 of colloidal films surrounding the soil particles. These films are 
 probably both organic and inorganic in nature and undergo altera- 
 tion under the influence of heat. By such alteration new surfaces 
 become exposed to the action of solvents, thereby making possible 
 the solution of materials otherwise effectively protected from the 
 solvents used. There is considerable evidence in the data, however, 
 that other changes were also produced by the heating. Some oxida- 
 tions must have taken place, and probably decompositions of other 
 types. Changes in the organic matter were produced at the higher 
 temperatures, as shown by the color of the water extracts. 
 
 Theeffectof heat on soil organic matter has been the subjectof some 
 previous investigation. It has been observed, for example, that 
 water extracts from heated soils are usually darker in color and con- 
 tain greater amounts of organic matter than similar extracts from 
 unheated soUs. 
 
 Darbishire and Russell l found that plants absorb more nitrogen 
 from soils that have been previously heated to 95° and 120° C. than 
 from unheated soils. They concluded that the heating brought about 
 some decompositions in the organic matter and also caused a modi- 
 fication in the bacterial flora. 
 
 i Jour. Agr. Sci., 2 (1907), p. 305. 
 
29 
 
 Pickering ! found that partial sterilization brought about an in- 
 crease in the solubility of the organic matter. An increase in the 
 total nitrogen soluble in water and greater absorption of nitrogen 
 by plants were also produced by heating. 
 
 Lyon and Bizzell 2 observed that the action of steam heat at 2 
 atmospheres pressure greatly increased the ammonia, in addition to 
 increasing the water soluble inorganic matter. The nitrates were 
 largely decomposed at this temperature and pressure. 
 
 Russell and Hutchinson 3 have shown that by heating some 
 Rothamsted soils at 98° C. for three hours a small increase in the 
 ammonia content took place. The most remarkable effect of the 
 partial sterilization, however, was in connection with subsequent 
 ammonification. Ammonia began to be formed in the course of a 
 few days, followed by a remarkable production of ammonia later on. 
 Corresponding to the increase in ammonia subsequent to heating, 
 an enormous increase in the numbers of microorganisms (bacteria 
 and fungi) took place. Heating to 125° also caused an initial pro- 
 duction of small amounts of ammonia, but no subsequent ammonifi- 
 cation set in. The nitrates were little affected although nitrification 
 was entirely inhibited by the treatment. From the fact that volatile 
 antiseptics bring about similar effects, these authors believe that 
 partial sterilization kills certain biological agents which, in the 
 untreated soil, effectively hold in check the multiplication and activ- 
 ity of the ammonifying organisms. After these inhibiting agents 
 are destroyed the ammonifying efficiency of the soil rises rapidly, 
 thus making available greatly increased amounts of nitrogen. 
 
 Lodge and Smith 4 found that decoctions from soils show an 
 increase in ammonia after steam sterilization at 15 pounds pressure, 
 but a decrease in ammonia took place from the sterilization of the 
 subsoil. 
 
 Lathrop and Brown 5 found that the amounts of ammonia and 
 total nitrogen soluble in water increased with an increase in the 
 pressure under which the soil was heated. At 10 atmospheres 
 approximately 40 per cent of the total nitrogen was rendered soluble, 
 while the ammonia thus split off was found to vary from 7.83 per 
 cent to 15.64 per cent. 
 
 Recently Schreiner and Lathrop 8 published a comprehensive 
 investigation of the effects of steam heat on soil organic matter. In 
 this work they isolated from heated soils a number of compounds 
 not found in the unheated soil. Among the compounds isolated a 
 
 i Jour. Agr. Sci., 2 (1908), p. 411. 
 
 * New York Cornell Sta Bui. 275 (1910). 
 •Jour. Agr. Sci., 3 (1909), pp. 111-144. 
 
 * Massachusetts Sta. Rpt. 1911, pt. 1, pp. 126-134. 
 •Jour. Indus, and Engin. Chem., 3 (1911), p. 657. 
 
 6 U. S. Dept. Agv., Bur. Soils Bui. 89; Jour. Amer. Chem. Soc, 34 (1912), pp. 1242-1259. 
 
30 
 
 number are nitrogenous and it is of special interest in this connection 
 that- practically all of these have been found to be beneficial to plant 
 growth. Certain nonnitrogenous bodies, however, were also isolated, 
 one of which, dihydroxystearic acid, seems to have been formed 
 under the action of heat and which has been found to be distinctly 
 toxic to plants. 1 It has been known for some time that steam heat 
 may bring about toxic conditions in soils, apparently of an organic 
 nature, but it remained for Schreiner and Lathrop to determine 
 definitely what is at least one of the toxic bodies thus produced. 
 On the one hand, these authors have shown that definite nitrogen 
 compounds of a character beneficial to plant growth are formed by 
 the action of heat, while on the other, a toxic compound, also organic 
 and definite in character, may be generated at the same time. The 
 significance of these discoveries is at once apparent; the value of 
 such definite and fundamental data can not fail to be important. 
 
 A knowledge of the effects of steam heat on soil organic matter has 
 special bearing on greenhouse practices, but may it not well be asked, 
 what are the effects of dry heat without pressure ? This phase of the 
 question has not been exhaustively studied. It is unsafe to conclude 
 a priori that the same types of cleavage and hydrolysis take place in 
 the absence as under the influence of pressure. There is evidence in 
 the growth and appearance of crops on burned soil that nitrogen is 
 made available by the heat. The deep green color of the crop is 
 sometimes very striking. It is important, therefore, that this phase 
 of the question be investigated in a general study of soil heating on 
 account of the importance of nitrogen in the nutrition of plants. 
 
 In an altogether different connection our attention was drawn to 
 the very large increase in the ammonia of some Hawaiian soils brought 
 about by the action of heat. It was observed that the ammonia con- 
 tent of certain soils increased from a few parts to over 400 parts per 
 million. At the same time the nitrates were decomposed. From 
 these observations and its general bearing on soil heating, an investi- 
 gation of the nitrogen transformations seemed of interest and impor- 
 tance. Whence the ammonia thus set free and from what class of 
 compound does it arise ? 
 
 The nitrogen of soils having been at one time bound up in organized 
 tissue, plant and animal, and, therefore, largely of proteid nature, 
 undergoes hydrolysis under the action of enzyms, bacteria, etc., with 
 the resulting formation or splitting off of simpler compounds. In 
 soils there must occur every stage of these changes from the proteid 
 complex, on the one hand, to inorganic compounds, on the other. The 
 larger part of soil nitrogen exists, however, in complex organic com- 
 binations. Nevertheless, the simple inorganic nitrogen compounds, 
 
 » U. S. Dept. Agr., Bur. Soils Bui. 80 (1911). 
 
31 
 
 especially nitrates, while occurring in relatively small amounts, have 
 long been considered to be of great importance to plant growth. 
 
 For the purposes of this investigation two courses of procedure 
 were open. First, a study of the changes that take place in the indi- 
 vidual nitrogen compounds occurring in soils; second, a study of the 
 group changes — that is, the effects of the treatment on the relative 
 amounts and proportions of the large groups included under the 
 amids, monamino acids, and' diamino acids. The latter of these was 
 chosen. 
 
 EFFECTS OF HEAT ON NITRATES. 
 
 The soils used in this investigation were taken from various locali- 
 ties in the islands and represent a wide range of types and conditions 
 of formation. Some of the samples were taken from arid sections, 
 some from intermediate, and still others from extremely humid sec- 
 tions. The method of heating differed somewhat from that employed 
 in the work already reported. The time of heating was 2 hours, 
 and the temperatures used were 100, 150, 200, 250° C. and steam heat 
 in an autoclave at 2 atmospheres pressure. One hundred gram por- 
 tions of air-dried soil placed in porcelain dishes were heated to the 
 desired temperatures in an air bath, or autoclave. Nitrates were 
 determined colorimetrically by use of the phenol disulphonic acid 
 method, and ammonia, from separate portions, by distillation with 
 magnesium oxid in the usual way. It should be remembered that 
 the ammonia thus obtained probably occurred in part as amids. 
 Distillation with magnesium oxid is known to liberate ammonia 
 from amids. In a lew instances the modified method of Schloesing, 1 
 which consists in leaching the soil with dilute hydrochloric acid and 
 then distilling the ammonia from the filtrate with the use of mag- 
 nesium oxid, was employed. The results were very similar to those 
 obtained by direct distillation. The following table shows the effects 
 of heat on the nitrate content : 
 
 The effects of heat on soil nitrates. 
 [Nitrate nitrogen expressed in parts per million of air-dried soil.] 
 
 Temperature. 
 
 Soil 
 No. 9. 
 
 Soil 
 No. 290. 
 
 Soil 
 No. 292. 
 
 Soil 
 No. 329. 
 
 Soil 
 No. 335. 
 
 Soil 
 No. 407. 
 
 Soil 
 No. 411. 
 
 Soil 
 No. 428. 
 
 
 108.0 
 95.0 
 
 57.0 
 5.0 
 5.4 
 
 94.0 
 
 18.0 
 18.6 
 12.5 
 6.5 
 .5 
 
 10.5 
 
 17.6 
 13.0 
 23.5 
 3.5 
 1.4 
 
 12.5 
 
 197.0 
 
 1.58.0 
 
 61.5 
 
 1.3 
 
 3.5 
 
 148.0 
 
 3.3 
 2.0 
 3.0 
 .6 
 1.0 
 
 L8 
 
 0.7 
 .7 
 .6 
 .5 
 .4 
 
 .6 
 
 56.0 
 
 60.0 
 
 1.7 
 
 1.5 
 
 .5 
 
 48.0 
 
 70.0 
 
 100° c 
 
 70.0 
 
 150°C 
 
 49.5 
 
 200°C 
 
 .8 
 
 250°C 
 
 .5 
 
 Steam pressure 2 at- 
 
 46.0 
 
 
 
 These data i 
 on soil nitrates 
 
 ire of interest 
 . In most in 
 
 as showing the destructive effect of heat 
 stances the nitrates underwent considera- 
 
 i Referred to by Todidi, Michigan Sta. Tech. Bui. 4, p. 1L 
 
32 
 
 ble decomposition at 150° C, while at 200 and 250° C. practically 
 total decomposition took place. Heating to 100° C. had but little 
 effect. Steam heat at 2 atmospheres pressure brought about some- 
 what less decomposition than dry heat at 150° C. 
 
 EFFECTS OF HEAT ON THE AMMONIA CONTENT. 
 
 In the next table will be found the data showing the effects of heat 
 on the ammonia content. 
 
 Effects of heat on the ammonia content of soils. 
 [Ammonia nitrogen expressed in parts per million of air-dried soil.] 
 
 Temperature. 
 
 Soil 
 No. 9. 
 
 Soil 
 
 No. 290. 
 
 Soil 
 No. 292. 
 
 Soil 
 No. 329. 
 
 Soil 
 No. 335. 
 
 Soil 
 No. 407. 
 
 Soil 
 No. 411. 
 
 Soil 
 
 No. 428. 
 
 
 28.0 
 23.8 
 67.2 
 187.6 
 40.6 
 
 83.3 
 
 18.1 
 
 19.6 
 
 45.2 
 
 464.8 
 
 206.5 
 
 51.1 
 
 11.2 
 
 10.5 
 
 32.2 
 
 174.3 
 
 336.0 
 
 16.8 
 
 56.0 
 64.4 
 81.6 
 218.4 
 28.0 
 
 77.7 
 
 12.6 
 
 18.2 
 17.5 
 32.2 
 19.6 
 
 16.1 
 
 9.1 
 13.5 
 
 28.7 
 368.2 
 114.8 
 
 46.2 
 
 19.6 
 28.0 
 77.7 
 170.8 
 98.0 
 
 69.2 
 
 63 7 
 
 oo°c 
 
 72 8 
 
 150°C 
 
 127 2 
 
 200°C 
 
 274 4 
 
 250 V C 
 
 238 
 
 Steam pressure, 2 at- 
 
 112 7 
 
 
 
 The ammonia content of soils Nos. 329 and 428 before heating is 
 here shown to be abnormally high. Generally soils contain ammonia 
 to the extent of a few parts per million only, whereas the nitrate con- 
 tent may rise to considerable concentration. 1 
 
 Under the influence of heat the ammonia content of all the soils 
 studied was greatly increased, practically reaching a maximum at 
 about 200° C. Above this temperature a falling off took place which 
 was probably due to a loss of ammonia through volatilization. We 
 here have, therefore, some interesting and, as seems probable, very 
 important facts. As pointed out above, heat considerably increases 
 the solubility of the inorganic matter. Here it is shown that the 
 ammonia content is enormously increased also. 
 
 Formerly little attention was given to the ammonia content of soils 
 except in its relation to nitrification. During the past few years, 
 however, the idea that ammonia may serve as a direct source of nitro- 
 gen to higher plants has steadily gained ground. It is now known 
 that certain aquatic plants, rice in particular, not only can utilize 
 ammonium nitrogen but that this form of nitrogen is better adapted 
 to assimilation by rice 2 than is nitrate. Other crops 3 have also 
 been found to be able to transform ammonia into proteids with 
 
 i Ammonia in soils, produced by biological agents, has for some time been looked upon as being merely 
 a transitional state, its formation being essential to nitrification. The nitrifying organisms seize on the 
 ammonia and convert it into nitrites and then into nitrates, thus effectively preventing an accumulation 
 of ammonia in the soil at any one time. One of the essentials of vigorous nitrification, however, is free 
 oxygen, while ammonirication may take the place under anaerobic conditions. In many Hawaiian soils 
 aeration is very low, and for this reason (perhaps others), nitrification frequently does not keep pace with 
 ammonification. 
 
 2 See Hawaiian Sta. Bui. 24. 
 
 s Kriiger, Landw. Jahrb., 34 (1905), No. 5, p. 761. 
 
33 
 
 equal facility. From the large number of cultures that have been 
 reported and the many observations made it is safe to assume that the 
 ammonia of natural soils is absorbed and assimilated to a greater or 
 less extent by nearly all plants. We may conclude, therefore, that 
 an important part of the action of heat on soils has to do with the pro- 
 duction of ammonia. 
 
 As previously stated, Schreiner and Lathrop (page 29) have shown 
 that the major portion of the organic nitrogen compounds, split off 
 from more complex bodies in soils under the action of heat, is also 
 beneficial to plant growth. With the additional production of rela- 
 tively large amounts of ammonia it is probable that marked stimu- 
 lation would result. 
 
 The effect of heat viewed from this standpoint is also of interest in 
 its relation to the effects of partial sterilization. As already stated, 
 one of the pronounced effects of partial sterilization, either with heat 
 or volatile antiseptics, is the abnormal ammonification thus induced 
 and which seems to be correlated with marked plant stimulation. 
 In some Hawaiian soils the effect of partial sterilization on subse- 
 quent ammonification has recently been found to be exceptionally 
 great. If the accumulation of ammonia as a result of partial sterili- 
 zation reacts beneficially on plants, we certainly have a right to con- 
 clude that its direct production by means of heat would also prove 
 stimulative to crops. 
 
 EFFECTS OF BRUSH BURNING IN THE FIELD. 
 
 With the view to determining the effects produced by burning 
 refuse, brush, etc., in the field, a few samples of soil from spots where 
 brush had been burned were examined at two different times. The 
 brush was burned about September 1 and the samples were taken 
 September 10 and November 7, respectively. Care was taken to 
 remove the ashes so as to secure portions of the uncontaminated 
 soil. Samples of unburned soil near by were taken at the same 
 time. Ammonia and nitrates were determined in the samples as 
 
 follows : 
 
 Effects of burning brush on soil nitrogen. 
 [Parts per million of nitrogen in air-dried soil.] 
 
 
 As nitratos. 
 
 As ammonia. 
 
 Laboratory No. 
 
 After 10 
 days. 
 
 Two 
 months 
 later. 
 
 After 10 
 days. 
 
 Two 
 
 months 
 
 later. 
 
 402 (burned ) 
 
 6.5 
 
 20.0 
 
 • 6.0 
 
 6.0 
 
 16.0 
 
 £2.0 
 
 5.5 
 18.0 
 8.0 
 8.0 
 22.0 
 52.0 
 
 50.4 
 39.2 
 161.0 
 21.0 
 77.0 
 8.4 
 
 100.8 
 
 402a (not burned; 
 
 70.0 
 
 403 (burned) 
 
 10H. 4 
 
 403a (not burned) 
 
 32. 2 
 
 404 (burned ) 
 
 114 S 
 
 
 30.8 
 
 
 
34 
 
 Here again it is shown that an increase in the ammonia and a de- 
 crease in nitrates takes place in soil heating. The content of ammo- 
 nia and nitrates at the end of two months is of special interest. The 
 above data show that not only is ammonia formed by the action of 
 heat but that subsequently ammonification took place at a greater 
 rate in two cases out of three than in the unburned soils. Nitrifica- 
 tion, however, was not restored under the existing field conditions. 
 It is probable that reinoculation with both the ammonifying and 
 nitrifying organisms gradually took place, but the lack of aeration 
 prevented the development of the nitrifying bacteria. These soils 
 had not been cultivated for two years previously and received no 
 tillage during the time of observation. It is not possible to state the 
 temperature to which the soil was heated in these instances. An ap- 
 proximate test applied in another locality, however, indicates that 
 the burning of small brush heaps similar to those burned on the soils 
 above discussed created a temperature of about 200° C. 6 inches 
 below the surface. The temperature would naturally vary greatly 
 from place to place. 
 
 EFFECTS OF HEAT ON THE ORGANIC NITROGEN. 
 
 Having found that large amounts of ammonia are formed from the 
 action of heat, a study of the organic nitrogen as affected by heat 
 seemed of interest. It is well known that ammonia is one of the 
 cleavage products of protein hydrolysis. It is also known that in 
 the destructive distillation of organic nitrogenous substances ammo- 
 nia is one of the decomposition products. It was observed that the 
 amounts of ammonia recovered from heated soils by means of dis- 
 tillation were not proportional to the total nitrogen present, but 
 seemed to depend largely on the type of the soil. The amount of 
 ammonia obtained, for example, from soil No. 335 was very much 
 less than that from the other samples studied (page 32). Ammonia, 
 therefore, was probably volatilized and driven out of the soil to a 
 greater extent in some instances than in others. Soil 335 is a sandy 
 soil composed very largely of coral sand (CaCO s ). In the foregoing 
 work total nitrogen determinations were not made. Hence it is im- 
 possible to correlate the rise and fall of ammonia with losses of 
 nitrogen. 
 
 In order to throw further light on these questions total nitrogen 
 and the several groups of nitrogen compounds rendered soluble in 
 boiling hydrochloric acid were studied. For this purpose the 
 method of Hausmann 1 as modified by Osborne and Harris 2 was ap- 
 plied. This method was devised for a study of protein chemistry, 
 but has been previously used by Jodidi and others in studying the 
 organic nitrogen of soils. 3 
 
 Ztachr. Physiol. Chem., 27 (1899), p. 95. Jour. Amer. Chem. Soc, 25 (1903), p. 323. 
 
 Michigan Sta. Tech. Bui., 4 (1909); Iowa Sta. Research Bui., 1 (1911). 
 
35 
 
 In this study total nitrogen, nitrates, ammonia, amids, diamino 
 acids, and monamino acids were determined. Nitrates and ammo- 
 nia were determined in the soil directly, while the groups f organic 
 compounds were determined in solutions obtained by boiling 50 
 grams of soil with 750 cubic centimeters of hydrochloric acid under 
 a reflux condenser for 10 hours, as outlined by Jodidi, filtering, 
 and making the filtrate up to 1 liter. 
 
 The organic nitrogen of soils, having at one time been bound up 
 largely in proteid combinations, may reasonably be expected to 
 yield hydrolytic products similar to those formed from protein. 
 But little is known, however, regarding the specific hydrolysis 
 induced by the microflora of the soil. It is not known, for example, 
 whether the protein molecule as a whole is broken down with the 
 ultimate liberation of ammonia from the several classes of protein 
 cleavage products in the same ratio in which nitrogen occurs in 
 them or whether certain of these groups yield inorganic or elementary 
 nitrogen more readily than others. 
 
 Samples of both heated and unheated soil were studied in this 
 connection. The former were subjected to a temperature of 200° 
 C. for a period of two hours, after which the same treatment and 
 determinations were made as in the unheated portions. The results 
 are recorded in the following table: 
 
 Nitrogen compounds in heated and unheated soils. 
 
 
 i 
 
 to 
 o 
 
 i 
 
 o 
 
 a 
 
 1 
 
 2 
 
 Ctj 
 
 1 
 
 £ 
 S 
 < 
 
 Soluble in hydrochloric acid. 
 
 Composition of hydro- 
 chloric acid soluble. 
 
 Soil numbers. 
 
 a 
 
 < 
 
 o 
 
 a 
 
 as 
 
 «8 
 
 o 
 
 a 
 
 as 
 
 a 8 
 o 
 
 3 
 
 o 
 
 
 03 
 
 '3 
 
 o 
 
 a 
 a 
 < 
 
 W3 
 
 1 
 
 < 
 
 o 
 
 a 
 
 — « 
 
 as 
 p 
 
 o 
 a 
 
 || 
 
 a a 
 
 o 
 
 3 
 
 Unheated: 
 
 379 
 
 P.ct. 
 0.546 
 .179 
 .504 
 .779 
 .396 
 
 .417 
 .178 
 .419 
 .608 
 .207 
 
 P.ct. 
 
 0.001 
 .0001 
 .0015 
 .0045 
 .0062 
 
 .0 
 .0 
 .0 
 .0 
 .0 
 
 P.ct. 
 0.001 
 .005 
 .006 
 .022 
 .001 
 
 .069 
 .036 
 .067 
 .031 
 .020 
 
 P.ct. 
 0.096 
 .042 
 .079 
 .129 
 .074 
 
 .098 
 .055 
 .103 
 
 .077 
 .039 
 
 P. ct. 
 0. 030 
 .018 
 .055 
 .029 
 .033 
 
 .034 
 .017 
 .019 
 023 
 .022 
 
 P.ct. 
 0.298 
 .100 
 .240 
 .363 
 .125 
 
 .168 
 .044 
 .092 
 .079 
 .028 
 
 P.ct. 
 0.426 
 .165 
 .381 
 .558 
 .239 
 
 .369 
 .152 
 .281 
 .210 
 .109 
 
 78.02 
 92. IS 
 75. 59 
 71.63 
 
 60.35 
 
 88.49 
 85.39 
 67.05 
 34. ,54 
 52.65 
 
 P.ct. 
 0.23 
 3.03 
 1.57 
 
 P.ct. 
 22.53 
 25.45 
 20.74 
 
 P.ct. 
 
 7.04 
 10.91 
 14.43 
 
 5.9 
 13.80 
 
 9.20 
 11.18 
 
 6.76 
 10.95 
 20.18 
 
 P.ct. 
 
 69. 95 
 
 405 
 
 406 
 
 66. 06 
 62.97 
 
 428 
 
 3.94i 23.12 
 .41 30.69 
 
 18.69! 26.56 
 23.68 36.18 
 23.84' 36.65 
 14.76 36.66 
 18.35 35.7! 
 
 65.05 
 
 447... 
 
 52 30 
 
 Heated: 
 
 379 
 
 4."> S3 
 
 405 
 
 406 
 
 28.95 
 32.74 
 
 428 
 
 37.62 
 
 447 
 
 25.69 
 
 
 
 
 
 Considering first the unheated soils, the nitrates and ammonia 
 are shown to constitute a relatively small percentage of the total 
 nitrogen and to vary greatly in the different soils examined. Soil 
 447 was found to contain the highest amount of nitrates, while in 
 No. 405 nitrates were present to the extent of only one part per 
 million. No. 428 contained an abnormally high ammonia content, 
 
36 
 
 while Nos. 405 and 406 also contained many times as much ammonia 
 as nitrates. 
 
 The relative amounts of nitrogen extracted by hydrochloric acid 
 also varied greatly. In soil No. 405, 92.18 per cent of the total 
 nitrogen went into solution, while No. 447 yielded only 60.35 per 
 cent of its nitrogen. Nos. 405 and 406 are soils that have been 
 devoted to aquatic agriculture (rice and taro) for many years, while 
 soils 379, 428, and 447 have been subjected to dry-land cultures. 
 
 The chemical decompositions and hydrolyses that take place 
 naturally in the organic matter of soils being brought about largely 
 by biological agents, it is probable that the range and types of such 
 reactions in submerged soils are somewhat different from those 
 taking place in well-aerated soils. There are several lines of reason- 
 ing not necessary to mention here that lead to this conclusion. 
 From this point of view, then, the biological effects on soil nitrogen 
 may reasonably be expected to be different in the two instances. 
 The nature of the organic matter originally incorporated with the 
 soil probably has some bearing on this question also. 
 
 Among the several groups of nitrogen compounds brought into 
 solution by hydrochloric acid it is noteworthy that the amids and 
 monamino acids constitute the main portion. The latter comprises 
 approximately two-third© of the total nitrogen dissolved. It should 
 be borne in mind, however, that the monamino nitrogen was deter- 
 mined by difference; that is, by subtracting the sum of the other 
 groups from the total nitrogen in solution. It is known, however, 
 that this difference is not made up entirely of monamino acids. 
 Jodidi 1 found, for example, that the monamino nitrogen group 
 in Iowa soils was made up of from 40.12 to 92.11 per cent of actual 
 monamino acids, the variation in this respect being dependent 
 in part on the treatment to which the soil had been previously 
 subjected. It is of interest that the relative amounts of amids, 
 monamino, and diamino nitrogen in Hawaiian soils were found 
 similar to those of soils elsewhere. 
 
 Turning now to the question of heat as affecting soil nitrogen, it 
 was found that with the exception of No. 405 the average loss of 
 nitrogen was about 25 per cent, but in certain soils the loss was 
 much greater than in others. Soil No. 447 suffered a loss of prac- 
 tically 50 per cent while No. 405 sustained almost no loss of nitrogen. 
 It is also of interest that the reduction in the amounts of nitrogen 
 extracted by hydrochloric acid was greater in two instances and less 
 in three than the absolute loss of nitrogen occasioned by heat. In 
 every instance enormous increases in ammonia and a total decompo- 
 sition of nitrates took place. On the whole, the absolute amounts of 
 neither the amids nor the diamino acids were greatly affected by 
 
 'Iowa Sta. Research Bui. 1 (1911). 
 
 
37 
 
 heat, whereas there was relatively large reduction in the nitrogen of 
 the monamino acid group in every soil studied. 
 
 Heating, therefore, caused a loss of nitrogen on the one hand and 
 an increase in ammonia on the other, and the decompositions appear 
 to come principally from the monamino acid group. The amounts 
 of amids in soils Nos. 428 and 447 and the diamino acids in Nos. 406 
 and 447 also sustained considerable loss from the heating. 
 
 Regarding that portion of soil nitrogen remaining insoluble in 
 hydrochloric acid, next to nothing is known. By again referring 
 to the table (p. 35) it will be seen, however, that the heat had some 
 effect on the insoluble nitrogen compounds. The difference between 
 the total nitrogen in the soil and that extracted shows that consid- 
 erable reduction in the insoluble nitrogen of soils Nos. 379 and 447 
 took place by heating, while there was a gain in the insoluble nitro- 
 gen of soil No. 428. The organic matter of soil No. 428 is in a less 
 advanced stage of decomposition than that of the other soils studied 
 and it was noticed that a pronounced charring in this soil took 
 place under the action of the heat. It seems probable that such 
 charring of the organic matter would tend to protect the nitrogen 
 bodies in the interior of the particles from the action of the solvent, 
 thus apparently increasing the percentage of insoluble nitrogen. 
 
 SUMMARY. 
 
 (1) Twelve different soils representing a wide range of types and 
 agricultural conditions were studied with reference to the effects of 
 heating to 100° C, to 250° C, and to ignition. The solubility of 
 all the mineral constituents except sodium was determined, using 
 water and fifth-normal nitric acid as solvents. The effects on the 
 nitrogen compounds were also investigated. 
 
 (2) The results showed considerable variation. Neither the abso- 
 lute nor the relative solubility of the inorganic constituents were 
 effected similarly in all the samples studied. 
 
 (3) On the average, drying at 100° C. was found to bring about 
 an increase in the water soluble manganese, lime, magnesia, phos- 
 phoric acid, sulphates, and bicarbonates. At this temperature an 
 increase in the solubility of potash, silica, and alumina was pro- 
 duced in about 50 per cent of the soils examined, but a decrease 
 was observed in the solubility of these elements in some instances. 
 The solubility of iron was decreased in most instances. 
 
 (4) Heating to 250° C. or ignition produced effects on the solu- 
 bility in water similar to those brought about at 100° C, but vary- 
 ing in degree, these being sometimes greater, sometimes less in 
 intensity than those produced at 100° C. 
 
 (5) The solubility in fifth-normal nitric acid was not greatly 
 affected by heating to 100° C, but in some instances heating to 
 
38 
 
 250° C. considerably increased the solubility of alumina, manga- 
 nese, potash, and phosphoric acid and at the same time effected 
 a reduction in the solubility of lime and magnesia. Upon ignition 
 the solubility of silica, alumina, potash, phosphoric acid, and sul- 
 phates was increased, while the solubility of lime and magnesia 
 underwent a corresponding decrease. 
 
 (6) The solubility of soils used in aquatic agriculture is abnor- 
 mally high, but upon drying out these become much less soluble 
 and approach a state similar to that existing in aerated soils. When 
 such soils are heated after drying they seem to undergo changes of 
 the same order as are produced in dry-land soils. 
 
 (7) No single factor is sufficient to cover the solubility effects 
 resulting from heating Hawaiian soil. On the other hand, the 
 subject is very complex and involves many factors. Among the 
 more important of these may be mentioned flocculation, deoxida- 
 tion of manganese dioxid, oxidation, particularly of iron, double 
 decomposition, dehydration, and the attending physical alterations 
 of soil films. Such alteration would destroy film pressure, thus 
 allowing the solvent to come into more intimate contact with the 
 soil constituents. At the higher temperatures bicarbonates become 
 converted into normal carbonates, thus effectively lowering the solu- 
 bility of lime and magnesia. 
 
 (8) Nitrates undergo decomposition with heat, a decrease in 
 nitrate content having been found to take place at 150° C, while 
 at 200° or 250° C. practically total destruction of nitrates took 
 place. 
 
 (9) One of the noteworthy effects of soil heating is the production 
 of ammonia, which at 200° C. was formed in abnormally large 
 amounts. Soil subjected to heat from brush burned in the field 
 was found to undergo stimulated ammonification after heating. 
 Nitrification, on the other hand, was not restored after the lapse of 
 two months. 
 
 (10) Heating to 200° C. caused a loss of approximately 25 per 
 cent of the total nitrogen. A loss of nitrogen and the ammonia 
 formed by the action of heat came largely from the monamino 
 acid group, while the amids and diamino acid sustained much less 
 loss. 
 
 (11) The results of these studies are believed to throw important 
 light on the subject of soil aeration and consequently have a direct 
 bearing on the practical question of soil management. 
 

 UNIVERSITY OF FLORIDA 
 
 ■■Mill 
 
 3 1262 08929 1099