Jan., 1916
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
t h a t in t h e case of such substances, high in f a t , t h e use of t h e stirring rod is of no additional value although equally well suited t o t h e determination. The principal advantage t o be gained by t h e carbide method is t h a t of a definite end point. I n drying fats, t h e increase in weight due t o oxidation may introduce serious error. With t h e calcium carbide method, t h e end point is very clearly defined, a n d it is reasonable t o suppose t h a t oxidation is prevented b y t h e atmosphere of acetylene with which t h e fat is in contact. On t h e other hand, i t should be borne in mind t h a t in t h e case of a fat containing free glycerine some error may be introduced by t h e interaction between t h e carbide a n d t h e glycerine. This same fact should be taken into consideration in applying t h e method t o soaps, containing glycerine. The official method is, of course, equally faulty in such cases, due t o t h e difficulty of drying glycerine a n d t o t h e fact t h a t glycerine slowly volatilizes at t h e temperatures employed. The method as applied t o fruit juices requires further A few facts regarding t h e determinainvestigation. tion are worth noting, however, a t t h e present time. The presence of acid in t h e fruit juice causes some hydrolysis on continued heating, thus decreasing t h e apparent moisture content if t h e latter is determined b y t h e official method. Furthermore t h e presence of volatile compounds, such as acetic acid and alcohol, is a factor tending to increase the apparent moisture content. I n t h e carbide method t h e acids are also a source of error in t h a t they react with calcium carbide t o produce a calcium salt and acetylene. Attempt t o neutralize t h e acid would be valueless as the reaction would result in t h e formation of water which would similarly increase t h e apparent moisture present. T h e carbide method has a n advantage over a n y method depending upon t h e evaporation of t h e moisture, however, in t h a t t h e error may be definitely determined in each case a n d corrected for. Since t h e increase in apparent moisture due t o t h e action of t h e acid on the carbide is proportional t o t h e hydrogen ion concentration, i t is necessary t o determine only t h e total acidity of t h e juice a n d correct t h e volume of acetylene accordingly. The presence of alcohol does not influence t h e results by t h e carbide method unless present in sufficient concentration t o materially affect t h e vapor pressure within t h e burette or t o dissolve appreciable quantities of acetylene. CONCLUSIONS
of solids in the syrup sample a n d sand on which t h e syrup is dried. IV-The carbide which is used should be subjected t o a blank determination t o determine t h e water equivalent. V-The method is especially adapted t o substances easily denatured at high temperatures a n d t o those which lose other volatile substances (not permanent gases) during t h e usual process of drying. VI-The method can be used when acids are present b y correcting t h e volume of acetylene for t h e total acidity. DIVISION OF AGRICULTURALCHEMISTRY DEPARTMENT OB AGRICULTURE,UNIVERSITY OF MINNESOTA ST. P A U L I MINNESOTA
ACID SOILS AND THE EFFECT OF ACID PHOSPHATE AND OTHER FERTILIZERS UPON THEM By S. D. CONNER Received August 2, 1915 INTRODUCTION
Soil acidity is of such complex and variable character t h a t soil investigators have not been able t o agree as t o its exact nature. For a long time i t was supposed t o be due entirely t o the presence of organic acids. Humic acid was t h e name given t o t h e first of these. Afterwards ulmic acid, crenic acid and apocrenic acid were discovered. It is now generally held t h a t t h e above-named acids are not definite chemical compounds, b u t probably represent groups of organic compounds of a more or less acid character. They are generally spoken of by recent writers as "humic or humus acids." I n recent years inorganic compounds of a n acid reaction have been recognized as important factors in soil acidity. I n regard t o mineral soil acidity there is great difference of opinion as t o whether i t is of a chemical or a physical nature. Among t h e numerous contributors t o t h e literature on t h e subject may be mentioned: Cameron,' Kohler12 Parker13 H a r r i ~ ,Wiegner,5 ~ Gans16 Van Bemmelen,' Sullivanls Veitch,g Loew,'O and Daikuhara." T H E EFFECT O F S O L U B L E S A L T S O N A C I D S O I L S
Practically all methods for quantitatively estimating soil acidity depend upon t h e reactivity which t h e soil may have with bases: either free or combined. The reason different soil acidity methods do not give accordant results is due t o t h e variable composition of soils a n d t o t h e fact t h a t t h e various acid constituents of soils show different degrees of reactivity with 1
I-The calcium carbide method for moisture is accurate within three- or four-tenths of a per cent a n d equal in this respect t o t h e present official method of t h e A. 0. A. C. 11-The proposed method is more satisfactory t h a n t h e official method inasmuch as t h e end Doint is clearlv defined, a n d t h e determination may be completed within a much shorter period of time. 111-The official method is open t o criticism because of t h e uncertainty of results where there has been variation in stirring or variation in t h e relative amounts
35
2
8
F. K. Cameron, "The Soil Solution," 1911, p. 66. E. Kohler, Ztschr. Prakt. Geol. Jahrg., 11 (1903), 49. E. G. Parker, U.S. Dept. of Agr.. Jour. Agr. Res., 1, No. 3 (1913). J, E. J . Phys, Chem,, No, (1914), 355,
G. Wiegner. JOUY. Landw., 60, NO. 2. p. 111; s ( i g i z ) , 197. R . Gans, Internat. Mitt. Bodenk., 8, No. 6 (1913), 529-571; Centbl. M i n . Geol. U. Pol., No. 22. p. 699; 23 (1913), 728, and No. 9, p. 273; 10 6 8
(1914), 299. 7 J. M. Van Bemmelen, Deul. Chem. Ges. Ber., 11 (1879), 2223; Landw.
v e r s ~ ~ s . ~ . ~ ~ ~ l ~ ~Sur,, , h 'Bull, , 8 ~313) . (1907). ~eol,
9 F. P. Veitch, J . A m . Chem. Soc.. 26 (19041, 637: see also Hopkins, Pettit and Knox, U. S. Dept. Agr., Bur. Chem., Bull. 78 (1903). , a n ~ ~ o ~ ~ ~ ~ ~ ~ , "Sta., ~ ~u.~ ~Dept. ~cp Agr., 6 1 E xl3 p(1913); t'
s.
11
G. Daikuhara, Bull. I m p . Cen. E w p f . Sta. Japan, No. 1 (1914), 1-4.
T H E J O U R N A L O F I N D U S T R I A L A N D ENGINEERI-VG C H E X I S T R Y
36
different bases as well as with t h e same base when free, or when combined with different acids. T h e experiment reported in Table I v a s planned t o investigate this point. Neutral normal solutions of the various salts indicated were prepared with Cos-free water. The materials were as described in Table I. Ten grams of the silicate, or soil, were p u t v i t h I O O cc. of t h e salt solution, shaken a t intervals and allowed t o stand over night. Then it was again thoroughly shaken and immediately filtered, and refiltered through the same filter until the filtrate v;as clear. Twenty-five cc. aliquots of the filtrates were titrated with N / 2 0 N a O H solution, using phenolphthalein S e w 2 j cc. aliquots were analyzed for Al203 and Fe203. (There was no iron in the solution from aluminum silicate and a negligible trace only in the soil soltttions.) The determinations were all made a t t h e same time under uniform conditions of time a n d temperature, and with t h e same manipulation and reagents. Figs. I and I1 graphically present t h e d a t a in Table I and show t h a t the basic as well as t h e acid radicle of t h e salt varies the amount of acidity developed and t h a t this variation is not uniform with different soils. It will be seen from Table I t h a t while much higher acidities are obtained with acetates t h a n with strong acid salts, t h e amounts of A l g 0 3 found in solution are very much less with the acetates than with salts of strong acids. This is in accordance with the results obtained b y Parker.' The acidities obtained with salts of strong acids can be accounted for t o a large extent b y the presence of salts of aluminum. The aciditv obtained when acetates are used cannot
FIG.
I-RELATIVEACIDITYOB
SOILS W I T B V . 4 R I O U S N O R M A L S A L T S O L U T I O N S
be accounted for in this way. As there is so little a1uminu.m in solution and so much acid titrated, it is very evident t h a t the acidity with the acetate is due t o a free acid, and, in t h e case particularly of aluminum silicate, t h e acidity must be due t o free acetic acid. While these results are in accordance with adsorption theories, t h e y can also be explained on t h e basis of chemical double decomposition as follows: When potassium acetate, for instance, reacts with aluminum silicate, part of the potassium replaces part of t h e 1
E. G. Parker, U. S. Dept. Agr., Jour. A ~ YRes., . 1, T o . 3 (1913).
TABLEI-TRE.4ThlENT
OF SILICATE AND
SOILS
Vol. 8, SO.I
WITH
\rARIOUs
NORMAL
SALTS o ~ u r ~ o s s Constituents in percentages Volatile matter Humus
MATERIAL TREATED Artificial aluminum silicate (Merck's) Alz0,.7SiO~.lOHzO (by analysis). . . . , . . , , , , , , . . . 25.34 B Acid silty clay soil from Lawrence Co. Indiana. . 4.09 C Acid peaty sand soil' from La Porte Co. indiana. . . . 8 . I 6 D Acid peat soil, fro& Kosciusko Co.. Inhiana. . . . . . . 83.53
KO. A
DETERMISATION:
RELATIVEACIDITY Cc. 1V/20 NaOH to neutralize 25 cc. Salt used A B C D KzSOt. . . . . . . . . , . , 7.5 1.3 1.7 5.6 KCzHaOz . . . . . . , , . , 26.0 4 . 1 6 . 8 3 9 . 4 KC1. . , , , . . . . , . , , t . 3 2.5 2.1 3.2 Kh-03. , . . . . . . . , , , , 6 . 1 2 . 6 2 . 0 2.6 NazS01, . . . . . . . , , , 4.0 1 . 9 1 . 9 5.2 NaCzHaOz.3HzO.. . 18.9 3 . 5 6 . 2 37.7 NaCl. , , , , , , , , , , , 2.3 2.0 1.4 2.3 KahTOs., , , , . , . . , , , 2 . 0 1 . 9 1 . 9 2.2 Ca(CzHa0z)zHzO. , 17.4 3 . 5 7 . 7 43.7 CaCIz. . . . , . . . , , , 2.0 1 . 8 2 . 4 5.2 Ca(S03)2.4HzO. , . . 1 . 6 1 . 9 2 . 4 4.9 bIgS04.7HzO.. . . , . . 2 . 8 1 . 8 2 . 1 5.2 Mg(CZHaOn.)z.4HzO. 17.7 3 . 6 6 . 6 41.0 MgClz.GH20. . . . . . 2 . 4 2 . 3 2 . 0 3.4 Mp(N03)z.GHzO... . 2 . 4 2 . 3 2 . 9 4.5 Ba(CzHa0z)zHzO. . , 22.2 3 . 9 8 . 1 4 4 . 0 BaC12.2HzO. . . . . . , . 3 . 9 2 . 3 3 . 2 6.2
. . . .. . ..
.
Kone 0.58 4.86 44.45
A1203 DISSOLVED
Mgs. A1203 in 25 A B C 0 . 9 0 0 . 2 3 0 25 0 . 0 7 0.05 0 . 0 4 0 . 9 5 0.32 0 . 2 0 0 . 7 1 0.37 0 . 1 2 0.55 0 . 2 0 0.12 0.05 0.02 0 . 0 2 0.40 0.19 0.12 0.37 0 . 1 4 0 . 0 8 0.09 0 . 0 5 0 . 0 3 0.54 0.30 0 . 3 0 0 . 5 1 0.25 0.22 0 . 5 8 0.37 0 . 3 3 0 . 0 6 0.06 0.06 0.47 0.32 0.26 0.63 0.49 0 . 4 0 0.15 0.12 0 . 1 4 0 . 7 1 0.30 0 . 3 9
cc. D 0.32 0.03 0.32 0.37 0.21 0.00 0.17 0.13 0.02
0.53 0.46 0.60 0.0; 0.42 0.60 0.12
0 51
aluminum forming potassium aluminum silicate, t h e replaced aluminum combining with the acetic radicle t o form aluminum acetate. Aluminum acetate is soluble b u t very highly hydrolyzed. On hydrolysis t h e insoluble aluminum hydroxide would go out of solution, leaving free acetic acid in solution. Such double decomposition would go on until equilibrium was reached and in this way t h e presence of free acetic acid could be explained on a purely chemical basis. Parker1 explains selective adsorption of KC1 b y a soil a s being due first t o hydrolysis of t h e KC1, t h e n a subsequent adsorption of K O H by the soil, leaving HC1 free t o react in turn with the soil bases. If this hypothesis were correct then it would seem true
FIG.11-RELATIVE W E I G H T S
OF A h 0 8 DISSOLVEDFROM NORMAL SALTS O L U T I O N S
SOI1,S B Y V A R I O U S
t h a t any reaction which might take place between a K O H solution and an acid silicate would throw some light upon the subject. With this in view the following experiment was planned t o determine the heat of reaction between K O H and various silicates: Ten grams of silicate were placed in a pint vacuum bottle, and j o CC. of recently boiled distilled water of room temperature added and stirred. A Beckmann thermometer was placed in 1
E. G. Parker, C . S.Dept. Agr.. J o u r .
Apt'.
Res.. 1, h-0. 3 (1913)
Jan., 1916
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
t h e vacuum bottle and the temperature ‘of t h e mixture read: j o cc. of normal potassium hydroxide of t h e same temperature as t h e mixture in the bottle were then added and thoroughly mixed with t h e water solution of t h e silicate. The temperature was read again a t t h e end of five minutes.
37
soils high in organic matter a n d containing a n excess of calcium in t h e form of carbonate will set carbon dioxide free from a solution of potassium bicarbonate. EFFECT OF H E A T O K A C I D I T Y
As further evidence t h a t t h e degree of acidity of
a silicate is affected by the amount of water of constitution t h e different samples were subjected t o heat. I n every case t h e acidity was lowered as t h e water was driven off. T h e artificial aluminum silicate (Sample A) had no acidity by the potassium nitrate method after being subjected t o ignition a t bright red heat. Clay soils were very much reduced in acidity on ignition. Acid peat and acid peaty sand soils were rendered alkaline on burning. Soils and silicates also lost their affinity for lime, as determined by t h e Table I1 shows the relative increase in tempera- lime-water method. This fact has already been ture on t h e addition of KOH solution t o various alu- noted by 1Teitch.l This characteristic of acid soils minum silicates a n d also t h e relative acidity of t h e may be a partial explanation of t h e beneficial effect silicates as shown by t h e potassium nitrate method. It of t h e old European practice of “paring and burning’’ is seen t h a t t h e more acid a silicate is, the greater is the soil, as by such practice a large part of the harmful the heat evolved, a n d where no acidity is shown there acidity would be destroyed. is no heat given off. From t h e amount of heat evolved The foregoing results show t h a t by t h e addition of these results indicate very strongly t h a t t h e reaction various kinds of salt solutions t o acid soils, soluble between potassium hydroxide a n d aluminum silicate acids or acid-acting salts are set free. Without doubt is of a chemical rather t h a n of a physical nature. a soil containing no soluble salts would be sterile a n d Table I1 is also interesting in t h a t it shows two ex- for this reason manures a n d fertilizers containing solceptions t o Gans” hypothesis t h a t silicates showing 3 uble salts are used. When nitrates, chlorides and molecules of SiOz t o I of A1203 are acid, while those sulfates are used as fertilizers on acid soils, t h e immewith less t h a n 3SiO2 t o IA1203 are not acid. Pyro- diate tendency is for the base t o combine with t h e phyllite (4Si02 t o 1A1203 t o I H ~ O )is not acid while organic matter a n d t h e silicate in the soil and for t h e halloysite (zSiO2 t o 1 A l ~ 0 3t o 3H20) is acid. Kaolin- acid radicle t o combine with aluminum and t o a less ite with t h e same relative silica and alumina as halloy- extent with iron. Of course, some of the acid would site b u t with one less molecule of water is not acid. combine with t h e stronger bases, such as calcium @nd Thus it would seem t h a t t h e acid or alkaline state magnesium, b u t t h e acid condition of any soil is due of aluminum silicates depends upon the amount of t o the fact t h a t it does not have a sufficient supply water of constitution as well as upon t h e ratio of Si02 of the strong bases, hence aluminum and iron are forced t o supply the basic radicle for many of the soil t o A1203. The acidity of the sample of acid-washed kaolinite reactions. The immediate effect, then, of t h e addimay be accounted for because of the fact t h a t it con- tion of soluble salts of nitric, hydrochloric a n d sulfuric tains approximately 3 per cent less &03 a n d approx- acids would be t h e setting free of soluble aluminum imately 3 per cent more Si02 and about 0.j per cent and iron salts of these acids, a n d hence the presence more water t h a n t h e untreated kaolinite. Much in t h e soil of toxic acid solutions. Soluble salts of more aluminum t h a n silica was dissolved from the aluminum and iron have been found in unfertile kaolinite by t h e dilute hydrochloric acid. The orig- acid soils and t h e toxic character of aluminum nitrate inal sample of kaolinite did not contain any appre- studied in this laboratory.2 Soluble toxic iron and ciable amount of base other t h a n aluminum. I n this aluminum salts have also been found in acid soil a t connection i t may be well t o note t h a n Daikuhara2 t h e Massachusetts Station3 on plots receiving ambas reported work on a number of samples of kaolin, monium sulfate fertilization. Daikuhara4 reports minsome of which are acid, some neutral and others alkaline. eral soils which upon t h e addition of salts of strong N o soil samples were used in t h e heat of neutraliza- acids set free soluble acid salts of aluminum and iron, tion experiment, because it was found t h a t potassium thereby reducing their productivity. Veitchl says: Further t h a n this, t h e reaction which takes place hydroxide reacts with soil organic matter t o such a n extent t h a t more or less heat is evolved even with between certain of these soil constituents and added soils containing calcium carbonate. Many soils which chlorides, sulfates, etc., produces positively acid salts, are entirely satisfied SO f a r as calcium is concerned as we have seen from t h e reactions of t h e sodium are still unsatisfied SO far as potassium is concerned. chloride method. There can be but little doubt F. P. Veitch, J . A m . Chem. Soc., 26 (1904). 637. From work in this laboratory i t has been found t h a t
TABLE11-HEATS OF hyEUTRALIZATION(a) A N D RELATIVEACIDITIES( b ) O F VARIOUS SILICATZS WITH NORMALK O H Rise in temp. Acidity SILICATES FORMULAE(C)O C. (Lbs. ~~. CaCOs) 7120 A1zOa.7SiOz.lOHzO.. 1 . 9 1 Artificial aluminum silicate 2840 AlzOs.4SiOz.7HzO.. . 0.27 Montmorrillonite None Alz03.4SiOz.HzO... . Kone Pyrophyllite 1600 AlzOa.2SiOz.3HzO... 0.19 Halloysite None A1zOs.SiOz.. . . . . . . . None Cyaqite hTone AlzOs.2SiOz.2Hz0,. . None Kaolinite . . . . . . . . . . . . . . .0.07 840 Kaolinite (acid-washed) ..... ( a ) Heat evolved on adding 50 cc. normal K O H t o 10 g. silicate in 50 cc. water. ( b ) Acidity determined by potassium nitrate method as given in Bull. 107 (revised), Div. of Chem., U. S. Dept. of Agr. Amounts given represent pounds CaCOs needed to neutralize one million pounds silicate. ( c ) Formulae were confirmed b y analyses.
1
R. Gans, Internal. Mitt B o d e n k , 3, No. 6 (1913). 529-571. Daikuhara. Bull. Imp. Cen. Expt. Sla. Japan, No. 1 (1914).
* G.
* Abbott,
Conner and Smalley, Ind. Agr. Expt. Sta.. Bull. 170 (1913). Morse and Ruprecht, Mass. Agr. Expt. Sta., Bull. 161 (1915). 1 G. Daikuhara, Bull. Imp. Cen. E x p t Sla Japan, No. 1 (1914).
38
T H E J O U R N A L O F I N D U S T R I A L A N D ENGINEERIJVG C H E I W I S T R Y
t h a t i t is due partly, a t least, to the acidity thus produced t h a t the injury arising from the use of chlorides a n d ammonium sulfate on acid or neutral soils is t o be ascribed.” E F F E C T O F PHOSPHATES O N S O I L ACIDITY
the immediate effect Of Of the stronger acids on acid soils is t o increase t h e soluble acidity, this is not Ordinarily true in the case of salts of phosphoric acid. When phosphates are added as fertilizers t o Soils, even in t h e form of acid phosphate, the soluble phosphate is soon fixed and no increase of acidity follows. For the purpose of studying the effect of acid phosphate on acid soils an investigation was started b y the writer in August,, 1912, on field and laboratorytreated soils. FIELD-TREATED soxs-The samples of the fieldtreated soils were taken from Set IV East, Purdue Experiment Station. This set of plots has been under fertilizer treatment since 18go. Corn, oats, wheat, TABLE111-EFFECT OF ACID
PHOSPHATE O X
ACIDITIES
OF
ETHYL ACETATE METHOD FOR ESTIMATING I S SOILS
v01. 8, NO. 1
SOLUBLE ACIDITY
Weigh I O grams of soil into a glass stoppered bottle. Add 100 of a j per cent ethyl acetate solution, using freshly boiled and cooled distilled water. Shake a t intervals through the day and let settle over night. At the end of a definite period pipette out I O cc. of the clear supernatant solution and titrate with -AJ120 alkali, using phenolphthalein as an indicator, By repeating the shaking and titration at definite periods, the value CC.
of the velocity constant can be calculated, if desired, by using the formula for a monomolecular reaction represented by the equation I/’t log, u / u - x = IC. A blank j per cent ethyl acetate solution without soil should be carried as a check. A ~ 7 / ~ 0 acid 0 0 or salt solution can also be carried for comparison. The determination should be carried a t a constant temperature, preferably in a thermostat.
While this method is not advanced for the purpose of replacing any of t h e older soil acidity methods, it is believed t h a t it is valuable for use in a study of the nature of soil acidity. The results of t h e acidity determinations of Set
FIELD-TREATED S O I L S (SET
Iv EAST,PURDUE EXPERIM~NT STATION)
ACIDITIESOF SOILS (Alkali for Neutralization) ANALYSESOF SOILS (Set I V East, Purdue Expt. Sta.) Lbs. CaC08 Cc. N/ZO PLOT FERTILIZATIOS:1890-19 12 (inclusive) Nitrate per million h-aOH(c) Total lbs. per acre Per cent PER CENT ACID HUMUS Per cent nitrogen Potassium LimeEthyl TOTAL Per yo of total Pts. per nitrate water acetate Acid volatile HUMUS cent total nitrogen million method method method NO. (NHr)zSOd NaXOs phosphate KCl matter 1 None None None None 7.32 3.26 1.74 53.1 0.23 24 152 1607 10.5 2 (Q) PITone None Xone 7.99 3.60 2.00 55.6 0.26 80 112 1607 11.0 3 (b) None Xone None 8.21 3.77 1.94 51.5 0.26 87 60 1071 13.0 50 236 1428 10.5 4 1407 3382 2633 1258 7.59 3.42 2.00 58.5 0.24 5 None Kone None None 7.32 3.26 1.74 53.1 0.23 24 152 1607 10.5 6 1407 3382 2633 None 7.46 3.22 1.88 58.4 0.225 44 352 1964 9.5 7 None Xone 2633 1258 1.69 3.38 1.82 53.9 0,235 40 176 1607 9.5 8 1407 2382 Kone 1258 i.56 3.28 2.08 63.1 0.24 34 266 1607 9.0 9 None None None hrone 7.25 3.18 1.80 56.6 0.23 28 159 1607 10.0 7.40 3.14 1.68 53.5 0.23 40 143 1428 10.5 10 None None 2633 None 11 1407 3382 None None 7.21 3.05 1.84 60.3 0.225 32 364 1428 9.8 12 None None h-one 1258 7.26 3.03 1.74 57.4 0.22 32 216 1428 9.5 7.25 3.18 1.80 56.6 0.23 28 159 1607 10.0 13 None None None None (a) Horse manure 70 tons. ( b ) Cow manure 105 tons. (c) Cc. N/20 NaOH is the alkali required t o neutralize acidity developed by 10 g. soil acting on ethyl acetate for 115 hrs. at 21 C.
clover and orchard grass have been grown in a fiveyear rotation. The fertilizers and manure have been applied only to the corn, oats and wheat crops. The different plots have been treated with various manures as indicated in Table 111. On t h e plots receiving nitrogenous fertilizers, ammonium sulfate was used for t h e first five applications, then the treatment was changed and nine applications of sodium nitrate were made. For this reason t h e effect of t h e nitrogenous fertilization on soil acidity is not particularly significant as one type of fertilizer has tended to neutralize the effect of t h e other. that t h e soil of Set IV The analyses E,, is very uniform in character; hence i t is believed that chemical differences in soil samples f r o m the differe n t plots can be largely attributed t o t h e manurial treatment. Determinations of soil acidity were also made, the methods used being: The potassium nitrate method,’ the lime-water method of Veitch,2 a n d t h e ethyl acetate method. The procedure in the latter method is original in this work and so far as t h e author knows is used for t h e first time in estimating acidity in soils. 1 Hopkins, Petit and Knox, U. S. Dept. of Agr., Bur. Chem., Bull. 75 (1903). 2 LOC. Lit.
IV E., are shown in Table 111. I n all four instances t h e effect of t h e acid Phosphate has been to lower t h e acidity according t o t h e potassium nitrate method. I n t h e case of t h e ,lime-water method we find that Plot I O , which has received 2633 lbs. of acid phosphate per acre, is less acid t h a n t h e check plot receiving nothing. In 7 and 1 2 , and 6 a n d 11, t h e Phosphate appears t o have increased ferthe acidity. While comparing the tilizer, Plot 4, with the nitrogen a n d Potash, Plot 8, we find t h a t acid phosphate has decreased t h e acidity. Considering t h e results obtained with the ethyl acetate method we find t h a t in two cases there is more soluble acidity where t h e phosphate is used, in one case just t h e same acidity a n d in one case less acidity with acid phosphate than without. The ammonia test for acidity is sometimes used on soils high in organic matter. I n this test the soil containing t h e greater per cent of humus soluble in ammonia water wit,hout previous treatment with acid, is considered t h e more acid. I n Table I11 it will be seen t h a t in all four instances t h e soil having had acid phosphate applied contains less acid humus t h a n t h e correspondingly treated soil without acid phosphate. I n view of t h e fact t h a t in every case t h e soil receiving acid phosphate contains more total humus and more volatile matter t h a n the soil not receiving phosphate,
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Jan., 1916
i t would seem t h a t t h e tendency of acid phosphate has been t o render t h e organic matter less soluble in ammonia and hence the soil less acid. LABORATORY-TREATED s o I L s - I n view of t h e results obtained on t h e soils from t h e field plots, experiments were undertaken on soils treated with acid phosphate in t h e laboratory. The soils, as indicated in Table IV, were subjected t o t h e potassium nitrate a n d t o t h e ethyl acetate acidity methods. T o determine t h e effect on soil acidity, as shown by the potassium nitrate method, different phosphatic substances were applied t o soils K a n d D in equivalent amounts carrying t h e same content of phosphoric acid. This amount was based upon a n application of 8000 lbs. acid phosphate per acre, z,ooo,ooo lbs. of soil. The resulting acidity as shown by titration is less where t h e phosphoric acid is used t h a n it is with t h e untreated soil. All t h e phosphates, including acid phosphate, have given similar results. No. A C D E
K
L M
39
a great capacity for fixing phosphoric acid, it is doubtful if acid phosphate would ever be applied in amounts large enough to increase acidity. Very sandy or peaty soils low in aluminum a n d iron silicate might, in some cases, be a n exception t o this. Other acid soils were treated with acid phosphate in t h e laboratory, and in every test t h e potassium nitrate method indicated a decreased acidity in t h e treated soil. AS acid phosphate shows a distinct acidity toward phenolphthalein, which can be titrated, this decrease in acidity cannot be attributed t o a n apparent error of titration or t o a n effect of t h e phosphoric acid on the indicator. I n fact, as a rule, t h e less phosphoric acid there is in solution (as determined gravimetrically), t h e less there is of acidity indicated by the potassium nitrate method. When t h e effect of a n application of acid phosphate a t t h e rate of two tons per acre, z,ooo,ooo lbs. of soil, was tested by the ethyl acetate method, in the case of t h e artificial silicate and t h e mineral Montmorrillonite no acidity was indicated either with or without acid
TABLE IV-EFFECT OF ACID PHOSPHATE O N LABORATORY-TREATED SOILS Constituents in percentages Volatile matter Humus MATERIALTREATED Artificial aluminum silicate, Alz03.7SiOz.lOHzO (by analysis) None Acid peaty sand soil from La Porte Co., Indiana.. ........ 4.86 Acid peat soil from Kosciusko Co., I n d i a n a . . . . . . . . . . . . . . . . . . . . . . 83.53 44.45 Montmorrillonite (a natural silicate). AlzOa.4SiOz.7HzO. .. . . . . . . . . 21.02 None .~ Acid clay soil from Ripley Co., I n d i a n a . ~........................................................................ . 3.86 0.64 3.02 0.86 Acid silt soil from Jennings Co. Indiana.. Unfertilized acid loam from Set' I V E., Purdue Expt. Sta., Plots 9 and 13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.25 3.18 ~~
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RELATIVEACIDITIESBY POTASSIUM NITRATEMETHOD Results on 100 g. Soil Digested with 250 cc. N KNOi Results on 25 g. Soil Digested with 250 cc. N KNOs TREATMENT ACIDITY TREATMENT ACIDITY G. soluble PzOs OF Lbs. CaCOs per million G. acid Lbs. CaC03 per million per 250 cc. filtrate SAMPLE D K Dhosnhate C D L M C D L M None ........................................ 4000 4040 None 1835 2800 430 170 0.0025 0.0092 None 0.0010 3840 3960 0.05 . . . . . 140 .. .. 0.0010 0,0125 g. Phosphoric acid ..................... 140 0.024 g. Monocalcium phosphate.. . . . . . . . . . . . . 3760 3720 0.1 0.0010 li90(0) 2640 3io 200 O.OOls(a) 0 . oi04 0,0045 0.0010 0.2 0.034 g. Dicalcium phosphate.. . . . . . . . . . . . . . . . 3600 3120 E. Tricalcium uhosphate.. . . . . . . . . . . . . . . . 3520 3240 1725 2640 345 220 0,0020 0.03 0.4 0.0326 0.0038 0.0010 0 . 1 0 g. Acid phosphate;. .................... 3840 3840 0.8 1690 2960 415 300 0.0018 0,0520 0.0118 0,0048 0 . 0 5 g. Raw rock phosphate., ................. 3760 3800 1720 3200 610 400 0.0033 1.2 0.0918 0.0245 0.0140 t o 937 lbs. CaCOa 1 . 6per 1735 0.0038 3200 935 580 0.0918 0.0450 0.0250 ( a ) 0.2 g. acid phosphate alone titrates an acidity equal million and contains 0.023 g. soluble PzOs. RELATIVEACIDITIESBY ETHYL ACETATEMETHOD Cc. N,/20 NaOH per 10 g. Sample treated 100 hrs. a t 21.5' C. Acidity 100 cc. solution of various reagents TREATMENT A C D E K L M Cc. N/20 NaOH None 0.0 39.0 36.5 0.0 10.4 11.0 10.0 0.02 g. acid phosphate.. ......................... 1.5 0.0 37.5 37.0 0 . 0 8.4 8.0 8.0 N/lOOO nitric acid.. 33.0 0.02 g. acid phosphate N/1000 aluminum n i t r a t e . . ...................... 3.5
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Table I V also gives t h e results obtained with t h e potassium nitrate method on four typical acid soils when varying amounts of acid phosphate were added. One-tenth gram of acid phosphate per I O O grams soil represents a n application of one t o n per acre, z,ooo,ooo lbs. of soil. The acid phosphate used was ground t o pass a sieve I O O meshes t o t h e linear inch. It contained 1 1 . 5 per cent soluble P205 when 0 . z gram was digested with 2 5 0 cc. normal K N 0 2 . As t h e applications of acid phosphate were increased minimum acidities were reached; beyond this point further additions of acid phosphate caused the soluble acidity t o increase. The peat soil (D), which has only I . 5 per cent of mineral bases soluble in strong hydrochloric acid, shows t h e least power of fixing phosphoric acid. Apparently t h e power of fixation of P z O by ~ acid soils is due t o t h e inorganic more t h a n t h e organic compounds. If acid phosphate is applied in greater amounts t h a n t h e soil has t h e capacity t o fix, then t h e acidity is increased in proportion t o t h e acid phosphate applied. As ordinary soils have
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phosphate. I n every case except one, the addition of acid phosphate decreased t h e acidity of t h e soil. The peat soil proved a n exception by this test, showing slightly more acidity after a n application of acid phosphate. The 0 . 0 2 gram acid phosphate alone produced a n increase of acidity, yet when added t o ordinary soils it decreased t h e acidity even more than i t increased it when alone. The action of t h e solutions of N / ~ o o o nitric acid and of N / ~ o o aluminum o nitratearepresented t o give a n idea of the strength of the soluble soil acids. The results of t h e tests of the laboratory-treated soils (Table IV) confirm t h e results obtained with t h e field-treated soils (Table 111) and together they are believed t o be good proof t h a t the effect of acid phosphate when added t o acid soils in ordinary amounts is t o decrease soluble acidity and in fact any insoluble acidity which might become soluble a n d toxic by the application of fertilizer or other salts. I n this connection i t is interesting to note t h a t Meggittl reports 1 A. A. Meggitt, M e m . Dep. Agr. I n d i a , Chem. Ser., 3, 235 A. i., 1212 (1912).
T H E JOURiVAL OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
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a n experiment on a very acid soil in which t h e only plots which would grow grain were those which received alkaline manures and some which had superphosphate. The action of t h e latter manure in saving t h e crop notwithstanding the increased acidity(?) is attributed t o its stimulating action on root growth, which would result in increased oxidation and in the destruction of t h e toxic substance. I s it not more probable t h a t t h e superphosphate acted in a direct chemical way and t h u s precipitated the soluble acid toxic substance, and rendered it less harmful? The acid reaction of acid phosphate will no doubt exist in ordinary soils until fixation is complete. T h e rapidity with which such fixation may take place depends largely upon t h e physical condition and especially t h e water content of a soil. I n soils containing enough water for proper plant growth such fixation will occur in a very short time. Without doubt both organic and inorganic acids occur in acid soils and either class of acids may exist in a solubIe or a n insoluble form. It is doubtful if soluble inorganic acids ever occur in appreciable quantities in ordinary acid soils other t h a n as hydrolyzed salts of weak bases, such as aluminum and iron. Likewise i t is still more improbable t h a t free phosphoric acid or acid salts of phosphoric acid ever exist in ordinary soils. When calcium, magnesium or other strong bases are present the acid phosphate would be fixed b y these bases in a non-soluble form. I n acid soils deficient in strong bases aluminum and iron would largely furnish t h e base for fixation of phosphoric acid. Organic compounds are said by some t o aid in t h e fixation of phosphoric acid in acid soils;' on t h e other hand, a case is reported b y Petit,z where a forest soil rich in humus had n o power of fixing phosphoric acid. T h e reason acid phosphate and even free phosphoric acid tend t o reduce soluble and active soil acidity probably lies in t h e fact t h a t phosphoric acid tends t o form insoluble compounds, both organic and inorganic. Acid phosphate would tend t o hold iron and aluminum out of solution and hence in a non-acid form. The aluminum silicates containing the most water of constitution are the most acid; also they are the most active chemically. For this reason the phosphate would tend t o combine with these active alumin u m silicates and render them less acid. Such reaction could possibly go on until all the active aluminum was combined with phosphorus, leaving only calcium aluminum silicates or even free silicic acid. Probably three-fourths of the soils of Indiana are more or less acid. These acid soils, almost without exception, respond favorably t o fertilization with acid phosphate. Soils L and M which were used in p a r t of t h e experiments reported in this paper have in field fertilizer tests shown large crop increases after treatment with acid phosphate. Soil C does not respond favorably or unfavorably t o acid phosphate alone, b u t upon a partial neutralization by limestone i t does respond favorably t o such treatment. 1
Rousseaux and Brioux. Bull. .\!fern. Of. Renseig A g y . Paris, 8, No. 1
(1909). 2
A. Petit, Comfit. rend., 162 (1911); 155 (1912).
1701. 8. No.
I
The results of this paper are not advanced as a n argument in favor of acid phosphate as a remedial treatment for soil acidity. The author does believe, however, t h a t they show t h a t acid phosphate can be used without danger on phosphorus-deficient acid soils, either with or without the additional use of lime. S U M M A RY
I---Various acid constituents of soils show different degrees of reactivity with different bases, also with the same base when free or when combined with different acids. 2-The acidity developed when acid soils or silicates are treated v i t h neutral salt solutions is more probably d u e t o chemical exchange of bases t h a n t o physical selective adsorption. 3-When aluminum silicates are treated with a solution of potassium hydroxide, heat is developed with t h e acid silicates, b u t not with neutral silicates. The heat developed is proportional t o the acidity, indicating a chemical rather t h a n a physical reaction. +-The acidity of aluminum silicates is not only in proportion t o the ratio of A1203 t o Si02 but also in proportion t o t h e water of constitution. The greater the proportion of water in t h e silicate the more acid is the reaction. 5-Heating and t h e consequent driving off of water of constitution in acid aluminum silicates lower t h e acidity until all the water is removed when neutrality is reached. Ignition of acid soils also destroys the acidity. 6-Much of t h e harmful acidity of acid soils is due t o the presence of toxic acid salts of aluminum and iron. 7-The immediate effect of the addition of soluble fertilizer salts of the strong acids (nitric, hydrochloric and sulfuric) t o acid soils, is t o increase t h e soluble acid salts of aluminum and iron. 8-On experimental plots a t Purdue Experiment Station, soils treated for twenty years with acid phosphate show less acidity t h a n soils t h a t have never had acid phosphate. 9-Acid soils and silicates treated in t h e laboratory with acid phosphate show less soluble acidity than untreated soils and silicates. I -The reduction of soil acidity by acid phosphate is probably due principally t o a combination of t h e soluble phosphoric acid with t h e acid salts of aluminum and t h e consequent formation of insoluble nonacid compounds. 11--A new soil acidity method in which the catalysis of ethyl acetate is taken as t h e measure of t h e soluble soil actdity, is used along with the potassium nitrate method, and t h e limewater method of S'eitch. T h e author wishes t o express his appreciation t o hlr. Geo I. Spitzer and Mr. H. A. Noyes for many valuable suggestions. hToTE-since the completion of this article, the writer has received Bull. 162 of the Massachusetts Agricultural Experiment Station and it is gratifying to know that Dr. Brooks, the autho;, has concluded from a long-continued series of soil test experiments that acid phosphate (dissolved bone-black) a t least has not increased the necessity for lime. On the contrary, i t seems clear that the bone-black has reduced this necessity." ' I
PURDUEUNIVERSITY, LAFAYETTB, INDIANA
