Mar., 1914
T H E JOl’RLVdL O F 1,VDL’STRIAL A N D E,VGIiVEERIAVG C H E M I S T R Y
At t h e time t h e treated corn was sealed up the floats gave it a s a n d y feeling between t h e teeth, b u t in t h e silage from this corn the “ g r i t ” had disappeared. We were able t o detect no difference in the taste, odor or appearance of the two samples of silage. T h e following phosphorus estimations were made ,on these two samples of silage a n d on the fresh materials from which they were prepared. AND PHOSPHORUS IN SILAGE CORNWITH A N D WITHOUT A D D E D FLOATS, IN SILAGE MADEFROM THE SAME. PER CENT, WATER-FREE BASIS InorTotal
ganic P water Water- Citrate- sol. in sol sol. sol. 0.27, citrate-sol. P P HC1 P
+
Total
:
PRODUCT
0,200 0.203 0.218 0.207
0.151 0.150 0,147 0.149
0.020 0.021 0.021 0.021
0.086 0.082 0.082
...
0.083
0,170
0.231 0.228 0.214 0.224
0.159 0.161 0,161 0.160
0.009 0.007 0.009 0.008
0.112 0.110 0.112 0.111
Green silage corn plus floats (250 : 1) . . . . . . . . . . . . . . . . 0 . 3 7 4 0.371 0.367 0.371 Average.
0.135 0.138 0.135 0.136
0.055 0.064 0.065 0.061
0.156 0.181 0.178 0.172
0.158 0.157 0.155 0.157
0.061 0.061 0.059 0.060
0.234 0,243 0.235 0.23i
Untreated green silage corn
Average,
................
Silage from untreated corn.
Average.
.
................
................
Silage from treated corn..
...
Average.. . . . . . . . . . . . . . . .
0.405 0.387 0.361 0.384
... ,.,
...
... ,..
0.168
... ...
...
0.197
’
23
The citrate-soluble phosphorus in the treated fodder and in the silage from t h e same was naturally higher t h a n in t h e untreated corn a n d silage, since a part of the phosphorus of t h e floats was citrate-soluble. There was no increase in citrate-soluble phosphorus, however, in t h e residue from t h e water extraction. during t h e ensilage of the phosphated corn. The very considerable increase in inorganic phosphorus soluble in 0.2 per cent HC1 during t h e ensilage of the phosphated corn gives us the most significant figure of t h e test. In t h e treated corn fodder t h e inorganic phosphorus soluble in 0.2 per cent HC1 was 46.4 per cent of the total, while in the silage from t h e same was 61.7 per cent of t h e total. It is also of interest t h a t the phosphated silage contained more t h a n twice as much inorganic phosphorus soluble in 0.2 per cent HC1 as t h e treated silage. T h e total phosphorus of t h e floats was 12.666 per cent, the water-soluble phosphorus 0.01 29 per cent a n d the phosphorus soluble in 0.2 per cent HC1 8.721 per cent, all on a water-free basis. CoivcLvsIoN-The ensilage of ‘corn will render soluble in 0.2 per cent HC1 such a n amount of the phosphorus of floats, added t o corn, as t o constitute a practical consideration in t h e feeding of livestock. DEPARTMENT OF NUTRITION OHIO AGRICULTURAL EXPERIMENT STATION WOOSTER
... 0.217
T h e increase in total phosphorus during t h e ensilage pnocess shows t h a t there was a loss of 8 . 2 per cent of dry substance from t h e untreated corn a n d 3.5 per cent from the phosphated corn. T h e increase in water-soluble phosphorus in t h e untreated corn was not quite equal (7.4 per cent) t o the arithmetical increase due t o t h e loss of dry matter. During the ensilage of this untreated corn there was a loss of citrate-soluble phosphorus, in t h e residue from water extraction, which signifies a process of reversion t o less soluble forms. T h e one significant increase during t h e ensilage of the untreated corn was in t h e inorganic phosphorus soluble in 0.2 per cent HC1. This was much more t h a n enough t o account for arithmetical increase from loss of dry substance. I n the phosphated corn there was a loss of watersoluble phosphorus simply through the addition of t h e floats, t h a t is, t h e water-soluble phosphorus in the fresh corn was 0.149 per cent a n d in t h e phosphated corn 0.136 per cent, which probably signifies a combination of water-soluble phosphorus of t h e corn with bases in the floats. This probably took place during the partial drying a t 50’ C., though perhaps to some extent during the subsequent storage of t h e sample for nearly a year before t h e analyses were made. The water-soluble phosphorus in t h e phosphated silage was not higher t h a n in the untreated silage. T h e excess of water-soluble phosphorus in the phosphated silage over t h e amount in t h e unensiled. phosphated corn was more t h a n enough t o account for the loss in dry matter, b u t was not as great in amount as in t h e silage from t h e untreated corn, again suggesting reversion.
2
T H E EFFECT O F HEAT UPON THE SOLUBILITY O F T H E MINERAL CONSTITUENTS O F T H E SOIL‘ By WILLIAMMCGEORGE 2 Received November 5, 1913
Heating soils as a means of stimulating growth of crops is a practice established centuries ago, b u t owing t o t h e difficulties encountered in its application i t has not been extensively used in practical agriculture, a n d consequently has gradually fallen out of use. Those who have investigated t h e cause of this stimulation have, as was t o be expected from t h e extremely complex nature of soils, differed in their results a n d conclusions. I t is certain, however, t h a t the phenomenon is not explainable b y a n y one theory, b u t the action is dependent upon the chemical, biological, a n d physical properties of t h e soil. In Hawaii certain crops are greatly influenced, both in color a n d vigor, by the mere burning of brush and undergronths of guava and lantana upon the surface. I n tropical soils, which receive practically no “rest,” it is probable t h a t the effects of heat are similar t o those derived from cultivation a n d aeration. m’ith but few exceptions i t is found necessary in Hawaii t o plow t h e new land a n d follow with thorough tillage a t frequent intervals fpr several mo’nths before planting. On the other hand t h e same results may be accomplished by means of heat. Investigators have studied this question from various standpoints, among these being the effect of t h e heat upon the solubility of the mineral constituents. However, the majority have confined their studies t o phosphoric acid ; several have included potash and nitrogen, 1
2
Published by permission of t h e Secretary of Agriculture. Assistant Chemist, Hawaii Agricultural Experiment Station
,
T H E J O U R N A L O F I N D U S T R I A L A,VD E i V G I N E E R l N G C H E M I S T R Y
224
while b u t comparatively few have gone beyond this a n d determined t h e effect upon t h e remaining soil constituents. The object of the work, here presented, was t o a d d t o t h e information regarding t h e effect of heat upon all the c o m k o n mineral constituents of the soil.. Distilled water a n d fifth-normal nitric acid were used as solvents. Probably t h e most valuable work on the solubility of t h e mineral constituents of soils is t o be found among the publications of t h e U. S. Bureau of Soils, their work being largely confined t o t h e use of water as solvent. I n a bulletin of this Bureau' King gives comparative results of work upon fresh and oven-dried soils which show the effect of heating t o 110' C. to be quite striking. On the average, more nitrates, phosphoric acid, sulfuric acid, carbonic acid, a n d silica were recovered from the oven-dried t h a n from the air-dried soil, while t h e average of t h e chlorine .determinations showed a decrease. N o determinations of basic constituents are given, but it is stated t h a t upon later investigation a n increase was found in t h e solubility of potash, lime, a n d magnesia in oven-dried soils. M E T H O D O F P R E P A R I K G EXTRACTS-Extracts Were made upon the soils in proportions of I part soil t o j of water or fifth-normal nitric acid. T h e conditions of t h e samples treated were air dry, heated t o 100' C. for eight hours, heated t o 2 5 0 ' C. for the same time a n d over the full flame of the Bunsen burner (in porcelain dishes). The latter were heated carefully a t first t o prevent dusting a n d finally for two hours over the full flame. Water extracts were obtained by shaking for one hour a n d allowing t o settle twenty-four hours and then filtering. Nitric acid extractions were made b y shaking for j hours a n d then filtering directly. TYPES OF SOIL-I~choosing the soils t o be used in this work a series of twelve soils were chosen, which included in a general way the normal a n d abnormal types, both physical a n d chemical, occurring on t h e islands. These include both red a n d yellow heavy clays, sandy a n d silty soils, highly manganiferous (9.74 per cent M n s 0 4 ) ,highly titaniferous ( 2 0 per cent TiOz) soils, a soil containing 8.7 per cent MgO, submerged soils both in t h e wet a n d subsequently air-dried states, a n d finally soils both high a n d low in organic matter. In this paper only the results will be discussed. T h e complete analytical data a n d a more comprehensive discussion will be found in a bulletin of t h e Hawaii Experiment Station.2 T h e elements determined were silica, alumina, iron, manganese, lime, magnesia, potash, sulfates, phosphoric acid and bicarbonates. The results obtained upon the solubility of t h e first three of these substances in water are rather inconsistent. This is probably due t o the slight solubility of these elements toward this solvent. On an average t h e solubility of alumina a n d silica increased with increase in temperature up t o ignition. Iron was most soluble in the air-dry sample. This latter fact is in direct harmony with former experiences, namely, t h a t under normal conditions in Hawaii, part of t h e iron exists in the form of U. S. Dept. Agr., Bur P l a n t I n d u s , Bull. 26 Agr. Expt. Sta., Bull 30.
* Hawaii
Vol. 6, NO. 3
ferrous compounds. Hawaiian soils, while characteristically basic, normally give a n acid reaction, due indirectly t o the high clay content and its accompanying poor aeration. Further confirmation of this fact is t o be found in a comparison of cultivated a n d uncultivated soils, in which the iron content of t h e latter is more soluble. Also, the solubility of iron in rice a n d taro soils, in the submerged state, is strikingly high, a n d is greatly decreased as a result of heat a n d its accompanying oxidation. The data obtained b y using N / j nitric acid as solvent disclose some very interesting facts, and give almost conclusive proof of a n increase in solubility of these three constituents as effected b y heat. The results indicate a, gradual increase with increase in temperature up t o ignition. These effects on the solubility, especially in water, are probably referable t o a number of causes. I t is primarily physical, being related t o a n alteration of t h e films surrounding the soil particles and t o a modification of t h e colloidal forms which these elements probably assume under t h e prevailing conditions. Dehydration and certain chemical alterations a t the higher temperatures would also tend towards increasing the solubility in acids through the action of heat upon the hydrated silicates. It has long been known t h a t certain hydrated silicates of aluminum become more soluble in acids as a direct effect of heat. The ancient a r t of alum manufacture took advantage of this fact. T h e samples highest in magnesia content show the greatest solubility of silica in i V / j nitric acid. The alumina was found t o be most soluble in the highly organic soils and in addition proved t o be considerably more soluble t h a n the iron in every sample. &fAKGANEsE-The solubility of manganese in water was greatest in the samples ignited, if it be permissible to draw conclusions from an average. However, t h e data were somewhat inconsistent a n d not in harmony with field conditions as induced by cultivation; t h a t is, a n analysis of t h e same soil cultivated a n d uncultivated showed a decrease in solubility as a result of aeration. Apparently the effect of heat upon the manganese is partly chemical as well as physical. The solubility of N / j nitric acid as affected by heat shows a remarkably consistent increase in solubility up t o 2 j o ' C., followed by a large decrease in t h e ignited samples. This is true with only two exceptions in the entire seI;ies. This element occurs in some Hawaiian soils in the form of concretions and hence is present, at least partially so, as manganese dioxide. But in t h e normal soils these are absent and here t h e manganese exists in a lower state of oxidation a n d hence in a more soluble form. I n each instance manganites or other salts may occur to a limited extent. With one exception t h e oxides of manganese are quite insoluble in nitric acid, this oxide being manganous oxide (hlnO). Therefore the solubility of the oxides would increase with increase in temperature, owing t o a decrease in state of oxidation, MnOs being converted into LInzOa and M n 3 0 4 , each of which are partially soluble in nitric acid for t h e reason t h a t they are combinations of t h e oxides LInO a n d SInO?. Since I I n , 0 4 contains the largest amount of N n O i t is
Mar., 1914
T H E J O C R N A L O F I S D L ' S T R I A L A N D E IV GI iV E E RI LVG C H E M I S T R Y
evident t h a t a t this temperature greater solubility in A', j H S O a would result, due t o t h e formation of this oxide. I n addition t o t h e above facts i t is known t h a t the action of heat on organic compounds of manganese, as well as other of its salts, is t o convert t h e m into oxides. LIME ASD xaGxEsIA-From a study of the data obtained from the determinations of these t w o elements it was found t h a t they were both most soluble in water in t h e samples heated t o 2 j 0 ' C., increasing with increase in temperature up t o 2 j 0 O C., a n d decreasing again upon ignition. I n nitric acid t h e lime is most soluble in t h e samples heated t o 100' C., and least soluble in t h e ignited samples. T h e general tendency is for t h e magnesia t o be affected in a similar way. T h u s we are led t o conclude t h a t t h e action of weak nitric acid in no way correlates with t h a t of distilled water. The highly organic soils proved t o hold t h e lime in the more soluble form. It is also worthy of note t h a t the effect of cultivation was t o cause a n increase in t h e solubility of these elements. Another i m p o r t a n t fact brought out was t h a t even though most of t h e soils used in this series show, from digestion with HC1 (sp. gr. r . I I j ) 7 a higher magnesia content t h a n lime, one four times as much, yet t h e lime with few exceptions is present in higher concentration in t h e extract. The effect of heat upon t h e solubility of these t w o elements is more striking t h a n are t h e results obtained from t h e remaining elements. It is highly probable t h a t the increased concentration of the water extract of t h e sample heated t o 100' C over t h e air-dried samples is t h e result of physical causes, namely destruction of t h e soil film a n d dehydration accompanied b y a slight decomposition of organic matter. On the other h a n d the samples heated t o 2 j 0 O C. undergo all t h e above transformations more completely a n d in addition suffer a more complete decomposition of organic matter. Since calcium a n d magnesium are t w o elements universally combined with organic m a t t e r in t h e soil there necessarily follows a n increase in solubility as a result of t h e more complete decomposition. T h e soils containing the highest per cent of organic m a t t e r contained these two elements in the most soluble form. The decrease in solubility of lime a n d magnesia in water upon t h e ignited samples a n d in nitric acid a t 250' C. a n d ignition is h a r d t o explain. It is undoubtedly partly due t o chemical changes in t h e soluble forms resulting f r o m the decomposition of the organic matter, also in the decrease in exposed surfaces as a result of t h e aggregation of t h e soil particles a n d other physical factors. I t is suggested t h a t one of the chemical changes taking place is t h a t of a replacement of t h e potash a n d soda in the silicates b y magnesium and calcium, as a direct result of heating. The data obtained in this work show a decided decrease in solubilitv of lime a n d a n increase in t h a t of potash upon ignition in a majority of t h e samples. I n addition t o the abovementioned factors a decrease in solubility a t ignition would be produced b y t h e conversion of the bicarbonates into normal carbonates, t h e latter being less
225
soluble. This would, of course, be more noticeable in the water extracts. POTASH-The soils heated t o 2jo' C. a n d ignition yield t h e more concentrated solution of potash, t h e average being in favor of t h e ignited soils. I t mas found t h a t the solubility of t h e potash was increased b y cultivation, a n d t h a t in the highly organic soil t o be t h e most soluble. T h e general ideas involved in t h e effect of heat will be dealt with more thoroughly in the discussion t o follow, a n d for this reason t h e solubility of t h e potash requires little comment a t this point. The fixing of potash is generally held t o be due t o hydrated silicates a n d organic matter. Cameron a n d Bell1 on continuously extracting a soil with water until no more potash dissolved, then grinding t h e sample a n d re-extracting7 found a n additional amount of potash t o be removed. This they attributed t o a colloidal aluminum silicate upon t h e surface of t h e particles, thus protecting t h e m from the action of t h e water as well as absorbing t h e potash. Dehydration a n d decomposition would therefore materially overcome t h e fixing power a n d t h e potash subsequently replaced by lime or magnesia would not become refixed during a short period, a n d heat would also liberate more potash from t h e insoluble form. P H O S P H O R I C ACID-The solubility of this constituent as affected b y heat indicates a minimum in t h e air-dry soils a n d t h e maximum in those heated t o 100' C. a n d 250' C. It is worthy of note t h a t phosphoric acid is more soluble in t h e uncultivated t h a n t h e cultivated soils, a n d t h a t the former decreases in solubility with increase in heat. T h e nitric acid extracts show a gradual increase in solubility with increase in heat, being most soluble in t h e ignited samples. Phosphoric acid exists in soils in t h e major part combined with iron, aluminum, magnesium, calcium a n d organic matter. I t may be in t h e ,form of basic phosphates, hydrogen phosphates, or as double phosphates in combination with more t h a n one element. I t is probably combined mostly with iron, aluminum a n d titanium in Hawaiian soils. Considerable work has been done upon the effect of heat upon the solubility of this constituent a n d attempts have been made t o draw conclusions from these results as t o its state of combination, t h a t is arhether organically or inorganically combined. Peterson2using N / 5 nitric acid found t h a t after oxidizing t h e organic matter with hydrogen peroxide there was no increase in solubility when t h e soil was subsequently heated t o 240' C. He concluded, therefore, t h a t t h e solubility of t h e mineral phosphates in soils is not increased up t o 240" C. T h e results obtained from t h e water extracts of Hawaiian soils indicate a decrease in solubility a t high temperatures due either t o a chemical change t o a form less soluble in water or a n increase in absorbing power of t h e soil. The increase a t r o o ' a n d 2 5 0 ' is undoubtedly partly due t o a destruction of organic matter and t o a breaking up of t h e colloidal film. The action of dilute nitric *acid is somewhat different i n that an increase in solubility upon ignition results, accompanied by that of silica and titanium. Iron and alumina
u, s, Dept, 2
.4gr,, B u r , Bull, 30, p , 2 6 , Wis. Exp. Sta.. Reseovch Bull. No. 19.
226
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
occur, in Hawaiian soils, t o a certain extent as hydrates or hydrated silicates, and, of course, would be more or less mechanically impregnated with phosphoric acid, as well as chemically combined. T h e effect of heat would directly increase t h e solubility of these constituents in nitric acid u p t o ignition, a t which point t h e decomposition of t h e hydrates would be a t a maximum while their colloidal properties would be practically nil. SuLFATEs-Heat has a very striking effect upon the solubility of sulfates, most marked in t h e water extracts. I n this series t h e air-dried soils were t h e least soluble, those heated t o 100' C. next, while the maxim u m was reached in those samples heated t o 250' C., finally decreasing upon ignition. On t h e other hand t h e ignited samples gave t h e most concentrated solution with nitric acid. One surprising feature of this series is t h a t in many instances t h e sulfates were more soluble in water t h a n i n nitric acid, which is probably d u e t o precipitation subsequent t o extraction in the latter. I n connection with t h e solubility of the sulfates it should be mentioned t h a t part of t h e increase in solubility of sulfates as a result of heat is probably due t o absorption of the products of combustion of t h e gas used in heating t h e soils. King,' however, found a n enormous increase in t h e solubility of sulfates upon heating in an oven a t 110' C., using both gasoline a n d kerosene, t h u s eliminating this factor. I n addition t o t h e destruction of organic matter, soil films, etc., it is necessary t o take into consideration t h e effect of heat upon t h e various inorganic sulfur compounds. Calcium sulfate is known t o exist in four forms, two being anhydrous, one more soluble t h a n t h e other. Sulfur also exists in soils as sulfides, generally with iron or as sulfate in combination with iron, lime or magnesia, as well as many essential forms of organic compounds. T h e effect of heat would be most marked upon t h e organic compounds in that t h e y would be oxidized a t the higher temperature, t o the dioxide or trioxide which upon treatment with water as solvent would tend to form sulfuric acid or sulfates to the extent of t h e soluble bases present. On ignition i t is evident t h a t sulfur, especially t h a t organically combined, would be volatilized upon ignition. An illustration of this action is well illustrated in the soil containing t h e highest amount of organic matter in t h e series. I n this sample t h e increase of the sample heated t o 100' C. over the dry-air sample was 1600 parts per million, while in passing from 2 5 0 ' C. t o ignition t h e decrease amounted to 1900 parts per million. BICARBONATES--?;he results Of this series indicate a slight increase in solubility a t roo' C. a n d 250' C., followed by a decrease upon ignition. T h u s it appears t h a t heat increases t h e amount of bicarbonates in the soil a n d a t t h e same time increases the solubility of the bases. T h e decrease upon ignition is piobably due t o t h e transformation of t h e bicarbonates into normal carbonates, thus ternpoiarily reducing their sol'ubility * in water. b DIsCussIoN-The foregoing results show that a n increase in solubility of the mineral constituents of l
U. S. Dept. Agr.. Bur. Soils, Bull. 26, p. 56
Vol. 6, No. 3
Hawaiian soils is effected by heating. It was t o be expected t h a t t h e results would be inconsistent, t o some extent, because Qf t h e varying types of soil used. T h e samples represent most of t h e normal a n d abnormal types of t h e islands. T h a t there are both chemical and physical factors concerned in the phenomena a t hand must be admitted a t t h e outset. However, t h e most important set of factors affecting t h e solubility of inorganic soil constituents appears to be of a physical nature. Undoubtedly t h e means b y which t h e physical factors act is through t h e soil moisture in its relation t o t h e physical properties of t h e soil. The conditions conducive to t h e formation of a colloidal state a n d t h e subsequent relation of heat t o t h e destruction of colloid are t w o of t h e most important of these factors. It is certain t h a t soil moisture distributes itself around t h e soil particles a n d in some instances as a n impregnation within t h e particles. T h e moisture, therefore, occurs as thin films which, according t o certain physical conceptions, must be held arouqd t h e particle b y a n enormous pressure. From purely physical considerations this pressure has been estimated a t several thousand atmospheres. Under such pressure t h e concentration of film water with reference t o t h e mineral matter should be much greater t h a n t h a t of the free or capillary water in t h e soil. Then the air-dried soil, t h e particles of which are still surrounded b y a film of moisture, when shaken with water, should theoretically show the least solubility. Our results in most instances are in harmony with this assumption. B u t if t h e soil be allowed t o remain in t h e condition a n d environment prevailing in submerged cultures, t h a t is, in the presence of a large excess of water, then in time diffusion would bring a b o u t a more or less equal distribution of dissolved materials throughout t h e entire water present, and, therefore, the pressure of soil films would be decreased t o a minimum or entirely eliminated. Hence t h e amount of materials going into solution in t h e free water present from such soils would be expected to be abnormally high. Upon air drying such soils t h e normal films would again appear with a resulting decrease in solubility. Subsequent heating ought then t o affect these soils in a way very similar t o t h a t produced on dry land soils. The d a t a obtained in the examination of rice soils is in harmony with this view. Water, however, not only exercises a solvent action on minerals, but forms various hydrates, t h e solubility a n d physical character of which in some inst'ances are greatly altered; organic as well as inorganic matter goes into solution with the result t h a t t h e moisture films around the particles become solution films, holding in suspension and more or less intermingled with colloids, both organic a n d inorganic. The films then may be looked upon as being of a colloidal nature.' Upon heating the soil t o 100' C. alterations in the films would take place through evaporation a n d by partial dehydration of colloids t h u s destroying the pressure b y which the film was previously held around the particles. At the temperature of 100' C. t h e conNo claim is made for originality in this view. The idea of soil films, colloidal films, jels. etc.. has been made use of by various writers on soils.
Mar., 1914
T H E J O r R - V A L O F 1 , V D C S T R I A L A N D E Y G I N E E RI N G C H E MI: T R Y
centration of t h e soil moisture would also be tempo- able t o expect soils with widely varying physical a n d rarily increased, due t o increase in solubility with heat. chemical properties, such as t h e samples used in this During t h e course of t h e evaporation t h e concentration series, t o vary widely in their absorptive power. Hence of t h e soil moisture would increase t o t h e saturation i t is not at all unlikely t h a t t h e lack of consistency i n point, after which t h e mineral matternrould bedeposited some of t h e results obtained is due primarily t o this on t h e surface of t h e film as evaporation went on.' factor. Not only is there lack of uniformity in t h e Also t h e materials held in solution in t h e interior absorptive power of soils b u t they also show considerof t h e permeable particles would be partially deposited able selective power in t h e absorption of mineral conon t h e surface a s t h e water evaporated. Upon adding stituents. Soils high i n humus should tend t o have a water t o t h e soil after having been dried, it is probable high fixing power, due t o t h e properties of this cont h e materials deposited from previous evaporation stituent of chemically combining with minerals as well would be more soluble t h a n t h e other mineral constit- as i t s power of absorption, a n d , therefore, the effect uents. In addition a certain amount of oxidation a n d of heat upon highly organic soils should tend t o increase other chemical changes in t h e organic matter might t h e solubility of t h e minerals. This was found t o be reasonably be expected t o t a k e place, which would true in t h e highly organic soils of t h e series. Another have some effect on t h e solubility of t h e mineral bases factor is t h a t of precipitation following extraction, being t h e more marked in t h e acid extract due t o a t h a t tend t o combine with t h e organic matter. Upon shaking with water a soil previously dried, t h e more complete extraction. I n passing from 2 5 0 ° C. t o ignition t h e effects are solution then obtained should be of a greater concentration t h a n t h a t prepared from t h e air-dried soil. apparently of a specific rather t h a n general nature, With t h e absence of soil films a n d a more or less altered which have been previously discussed. Among these condition of t h e colloids present t h e solvent mould are t h e volatilization of certain sulfur compounds, have more ready access t o t h e soil particles during a conversion of bicarbonates into normal carbonates, deshort period in addition t o coming into immediate hydration of silicates, etc., replacing of potash b y lime contact with salts deposited on t h e surface of t h e par- and other chemical transformations. I n addition ticles. I n t h e light of these views then t h e solubility there is produced a greater aggregation of t h e soil parof soils before a n d after drying becomes more intel- ticles, resulting i n a decrease in surface area exposed t o t h e solvent a n d a n accompanying change in t h e fixing ligible. W h y several of t h e mineral constituents of t h e soil and absorbing powers of t h e soil. It is possible, b y should be so markedly more soluble when heated t o application of these conceptions, t o explain t h e majority 250' C. t h a n at t h e other temperatures is a question of changes, both increases a n d decreases in solubility not easily answered. T h e difference i n physical effects resulting from ignition. were quite noticeable in t h a t there was a greater aggreAcknowledgments are hereby extended t o Dr. W. gation of particles. Again there was a more complete P. Kelly, chemist a t this Station, for valuable suggesdestruction of organic matter effected at this tempera- tions and assistance otherwise rendered. ture a n d also i t is not entirely impossible t h a t drying HAWAIIEXPEXIMEKT STATION HOXOLULU at 100' C. for eight hours does not effect a complete elimination of t h e soil moisture a n d especially t h e water of chemical combination. It seems reasonable then THE USE OF S O D I U M CITRATE F O R THE DETERMINAT I O N OF REVERTED P H O S P H O R I C ACID' t h a t t h e effects of heating t o 100' C. are simply magBy ALFREDW. BOSWORTH nified when heated t o 250' C. added t o this being a more complete destruction of organic matter, t h e reI n 1871, Fresenius, Neubauer a n d Luck2 published sults both physical a n d chemical being of t h e same a method for t h e determination of reverted phosphoric general nature b u t more complete a t t h e higher tem- acid in phosphates which involves t h e use of a solution perature. The destruction of organic constituents of neutral ammonium citrate, specific gravity 1.09. being more complete would necessarily increase t h e This method, with a change in t h e temperature of solubility of the mineral matter held in combination, t h e solvent, has been in constant use since t h a t time3 a s i t is generally conceded t h a t t h e organic constituents with no a t t e m p t b y a n y one t o give a n explanation of t h e soil in i t s natural state are quite insoluble in of t h e chemical reaction involved. It has been quite water and acids, more especially t h e former. There is generally believed t h a t t h e neutral ammonium citrate also evidence of t h e existence of f a t t y or resinous or- solution possesses a selective power which enables ganic matter which would materially affect t h e prop- i t t o separate dicalcic-phosphate from tricalcic-phoserties of the soil film. For t h e decomposition of such phate. This is not true, for it has been found i n this bodies i t would be necessary t o heat t h e soils consider- laboratory t h a t IOO cc. of t h e Official ammonium citably above 100' C. rate solution2 is capable of dissolving 1.3, grams of I n addition t o t h e above-mentioned effects of heat precipitated tricalcic-phosphate i n one-half hour a t t h e relation between solid a n d solvent would naturally a temperature of 65' C. This dissolving of t h e tribe affected b y other factors. Among these, would be calcic-phosphate is accompanied b y a precipitation absorption or "fixing power" of t h e soil.2 It is reason- of calcium citrate. King (loc. c i f . ) in discussing t h e relative solubilities of fresh and dried soils advanced this idea. Richter (Landw. Vers. Stat., 41 (1896), p. 269) found t h a t heating t h e soil increased t h e absorptive power of t h e soil for water
1 Read before t h e Association of Official Agricultural Chemists, Washington, D. C., Nov. 17, 1913. * 2. anal. Chem., 10, 133. 8 U. S. Dept. Agr., Bur. of C h e m , Bull. 101 (revised).
