Dec., 1914
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
as much soluble phosphoric acid as a n y stronger solution. T h e normal acid shows a slight decrease in yield in t h e second a n d third soils, a n d t h e N / s acid shows a decrease in every case. This agrees with t h e experience of Wood in t h a t a certain strength of acid is necessary t o get all t h e Pz06. However, it is not necessary t o use t h e concentrated acid as did Passernini. T h e stronger nitric acids indeed are objectionable because t h e y introduce certain difficulties by bringing down larger quantities of iron a n d aluminum. PERIOD O F ExTRAcTIoN-In each case 20 cc. of normal acid were used, a n d the per cent of Pz06 given is a n average of two closely agreeing checks. TABLE 11-PERIOD OF EXTRACTION VARIED Per cent P10s found in soil Period of extraction 1 hr.. . . . . . . . . . . . . . 2 hr . . . . . . . . . . . . . . . . 4 hr.. . . . . . . . . . .a , . 8 hr . . . . . . . . . . . . . . .
.
No. 1 0.499 0.513 0.501 0.517
No. 2 0.166 0.173 0.166 0.154
No. 3 0.053 0.054 0.068 0.059
I n one hour practically all t h e soluble PzOs is obtained. Two hours would be a liberal allowance a n d sufficient for all cases. Passernini boiled for I hour, which is a b o u t enough, b u t Williams boiled on t h e water b a t h for I O hours, which was much longer t h a n necessary. Pagnoul digested for t w o hours, which was a b o u t t h e right length of time. Hilgard employed t h e two-day period for digestion with concentrated "0,. IGNITION-Each sample was extracted for 2 hrs. with z o CC. N "03. TABLE 111-TIME
OF I G N I T I O N VARIED
Per cent P~os found in soil
Ignition at red heat
No. 1
No. 2
0
0.513 0.499 0.487
0.18 0.199 0.195
................ ................
hr 1 hr.. ...............
1/2
No. 3 0.054 0.046 0.041
I n these cases t h e effect of ignition would seem t o be similar t o t h a t obtained b y Lipman, i. e., t o decrease t h e amount of P z O ~ soluble in "03. Sample No. z shows practically no change, but t h e other t w o show appreciable decreases in the amounts of P z O ~ extracted, as the period of ignition lengthens a n d as between ignition a n d no ignition. SUMMARY
I-Acid weaker t h a n I N t o z N " 0 3 will not extract all t h e soluble phosphoric acid from a soil. 11-It is needless t o extract with the acid for a longer period t h a n z hours on t h e steam bath. soluble phosphoric 111-Ignition decreases t h e " 0 3 acid in t h e soils. UNIVERSITY OF C A L I F O R N I A
BERKELEY
COMPARISON OF SILICATES AND CARBONATES AS SOURCES OF LIME AND MAGNESIA FOR PLANTS By W. H. MACINTIRE AND L. G. WILLIS Received September 21, 1914
T h e amount of calcium carbonate in soils has long been considered a very i m p o r t a n t consideration in their chemical examination; b u t calcium silicate has not been accorded universal recognition as a n important source of lime for growing plants. T h e s a m e may be said of t h e corresponding forms of magnesia. I n determining soil carbonates by t h e present official method of t h e Association of Official Agricul-
IOOS
tural Chemists, we find t h a t practically every soil has a n apparent occurrence of carbonates, b u t a t the same time possessing, in most cases of humid soils, a lime requirement b y t h e Veitch method.' These two conditions-presence of appreciable amounts of carbonates a n d lime requirements, which indicate need of carbonates-are diametrically opposite, a n d were a soil t o contain carbonates under laboratory conditions i t would have no lime requirement. It is hard t o conceive of a soil having 0 . 2 7 per cent calcium carbonate a n d yet having a lime requirement of 3812 lbs. of C a C 0 3 per acre (3,500,ooo lbs. of soil); however, such results were obtained by t h e A. 0. A. C. method for COz a n d t h e Veitch lime requirement method, respectivelx, upon t h e loam soil of t h e farm a t this Station. This is strongly indicative of erroneous results from either one or possibly both of t h e methods cited. T h e work of Marr2 a n d t h e results reported b y t h e writers3 have shown t h a t some soils absolutely free of carbonates, through elimination by dilute acid digestion, will produce heavy evolution of COz from t h e action of boiling acid upon carbonaceous matter. Marr concluded from his work t h a t the use of 1:5o HCl, a n d boiling with greatly reduced pressure, gave correct results. Until recently, practically all of t h e methods advanced for t h e determination of soil carbonates were based upon t h e supposed necessity of boiling t h e soil with acid t o completely decompose carbonates a n d t o expel from solution t h e liberated T h e more recent work of t h e writers3 has dem, COZ. onstrated t h a t phosphoric acid is less active t h a n hydrochloric acid upon soil organic matter a n d t h a t I : 1 5 HaPo4 will liberate a n d expel from solution all carbonate COZ a t room temperature with about a 4-inch vacuum. In recent unpublished work t h e writers are making determinations upon treatments of about 400,000 pounds of limestone per 2 , 0 0 0 , 0 0 0 lbs. of soil a n d t h e carbonates from this treatment are entirely liberated by I : I j &Po4 with suction a n d without heat. T h e Association of Official Agricultural Chemists has recognized the incorrectness of its method a n d is now studying t h e two methods above cited. It will t h u s be seen t h a t in many cases all of t h e COZfound by analyses of soils when boiling with acid has been erroneously considered as in combination with lime, while t h e lime has occurred largely in t h e form of silicates a n d not as carbonates. CORRELATION
BETWEEN
ACIDITY
AND
ABSENCE
OB
CARBONATES
gait he^-,^ in a comprehensive study of a large number of Ohio soils, found t h a t almost invariably there was a close correlation between acidity, as indicated b y the litmus-paper test, a n d absence of carbonates b y his modification of the Marr method. We should probably note, however, t h a t the authors have found t h a t soils rich in silicates of calcium a n d magnesium,
8
Jour. A m . Chem. SOC.,24 (1902). 1120. Jour. Agr. Sci., Vol. 111. Part 2 . 155-160. Tenn. Sla. Bull., 100.
4
THISJOURNAL, 6 (1913). 138.
1
1006
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
b u t devoid of carbonates, will react alkaline toward litmus paper. The, litmus-paper test, then, will show acidity in t h e absence of carbonates, except when there is a considerable a m o u n t of t h e alkali-earth silicates. h - A T I V E O C C U R R E K C E O F S I L I C A T E S A K D T H E I R FORRIATION I N SOILS
It has been the observation of the senior author t h a t it is a rare exception t o find in the Eastern States a cultivated soil which will react alkaline t o litmus, unless i t has been limed. I t would seem, then, t h a t t h e crops of many of our soils are compelled t o secure much of their lime from t h e carbonate of lime formed b y t h e hydrolysis of calcium silicate in carbonated water. While t h e occurrence of natiVe lime silicates has received b u t scant consideration, there has been even less attention paid t o t h e formation of silicates from lime treatments. Total lime, determinations by one of t h e writers,’ upon t h e lime-treated plots of the Pennsylvania Station has shown t h a t t h e reaction between lime a n d silicates continues !ong after attaining alkaline conditions b y t h e satisfying of t h e i m m e d i a t e l i m e r e q u i r e m e n t . It was shown t h a t of t h e total increase of lime over the check plots as a result nf t h e l i n e treatments, nearly 3 j per cent was accumulated as silicates. Investigations recently reported from the Tennessee Station‘ have shown t h a t a m o u n t s of CaO, C a ( O H ) 2 a n d precipitated C a C 0 3 , in excess of requirements of acidity, have very quickly united with soil silicates. It was found t h a t t h e t o lime requirements, acted directly with silicates and without carbonation, as in the Veitch procedure, when t h e treatments were mixed throughout t h e soil. T h e precipitated carbonate seemed t o combine with siliceous materials as quickly as the oxide a n d hydrate. T h e same experiments have shown decidedly quicker reaction between siliceous soil compounds a n d t h e oxide, hydrate a n d precipitated carbonate t h a n between silicates a n d ground limestone, in excessive a m o u n t s of equal basicity. It was also shown t h a t though lime reacts extensively with siliceous materials t h e silicates formed function in t h e same manner as does t h e carbonate b u t t o a lesser degree, which means t h a t there i s conservation of l i m e in soils w h e n i t i s present as silicate.
1
Tenn. Bull.. 107.
12
satisfy lime requirement; a n d t h a t t h e lime of caustic or carbonate formed shortly combines with acid silicates, preventing a n y accumulation of carbonates as t h e result of treatments. Gardner a n d Brown’ found t h a t applications of burnt lime a n d ground limestone, in amounts indicated b y t h e Veitch method, reduced t h e average requirements of a large number of plots b y 71 a n d 7 2 per cent, respectively. T h e analyses for residual lime requirements were made about eight months after treatments. This strongly indicates t h a t t h e continued beneficial effects of moderate liming must necessarily have come from the carbonate of lime, which is derived from t h e silicates b y action of carbonated water. LITERATURE
Although the literature upon t h e beneficial effects of CaSiOl, u n d e r s u c h d e s i g n a t i o n , is exceedingly scant, a great many d a t a , offered as showing t h e continued good effects from field treatments of moderate amounts of burnt or carbonated lime, have been attributed directly t o the original oxide or carbonate, whereas t h e beneficial results have been due indirectly t o t h e original treatment, a n d directly t o t h e continuation of the lime as silicate in t h e soil. Mieth* advanced the query, “ C a n t h e lime of calcium silicate serve as plant food?” a n d he studied t h e question by water-culture experiments with oats. He concluded t h a t t h e COS exuded b y root activities served t o produce carbonated water, which decomposed the calcium silicate a n d formed free silicic acid a n d calcium bicarbonate. He further silicate should receive consideration as a source of lime for growing plants. Gregorie3 found, in water cultures of rye, t h a t calcium zeolite “stimulated both root a n d aerial development,’’ both of which were retarded by a n excess of C a C 0 3 . Immendorf4 regarded liming with lime containing soluble silica as beneficial in connection with the formation of zeolites. Pfeiffer,6 in reviewing literature a n d discussing the work of Immendorf, concluded t h a t the. preponderance of evidence indicated beneficial effects from the use of siliceous lime. Von FeilitzenG secured better results with the finest lime, which reacts most extensively with silicates as shown by results published b y this Stati~n.~ SILICATES AS SOURCES O F CARBONATES I N SOIL SOLUTIONS
B E N E F I C I A L E F F E C T S O F CALCIUM SILICATE
I n extensive plot work a t t h e Tennessee Station marked effects are noticeable from liming over a nine-year period, during which nine crops of cowpeas a n d nine of wheat have been grown, though only 1800 lbs. per acre of lime were applied-an amount just sufficient t o neutralize t h e acidity requirements indicated b y t h e Veitch method. It is very probable t h a t the present favorable results from liming nine years ago are due t o residues of lime in t h e form of calcium silicate a n d not t o calcium carbonate. I t has probably not been sufficiently emphasized, if emphasized a t all, t h a t the average amounts of lime applied are required t o neutralize “acidity” or t o
Vol. 6 , No.
T h e d a t a presented in Table I show t h e comparative amounts of lime a n d magnesia conveyable in solution as bicarbonates t o plants, from carbonates a n d silicates as t h e sources of the bases. These results were secured b y placing each charge, in the amounts designated, in joo cc. of distilled water in glass cylinders a n d passing a current of COS through the water for 4 hours continuously. T h e COZ entered a t t h e bottom of t h e cylinders a n d a t such a rate as t o Pa. Sla. Annual Report, 1910-11, 76. L a n d w . Vers. Sla., 74 (1910). No. 1. 8 1 , No. 2, 120. 8 E x p . Sla. Rec., 23, 5 2 7 . I b i d . . 26, 34. 6 I b i d . . 29, 520, and 80, 127. 6 I b i d . , 23, 426. 7 Lac Lit. 1
2
Dec., r g r q
T H E J O l . R A ' A L 01;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
keep t h c substances in suspension. At the end of the 4-hour period, the suspended matter was quickly removed by filtration through Euchner filters with suction and the solutions titrated with h T / macid, methyl oranre being.used 3s an indicator. I t will be noted t h a t
1007
soil, No treatments other t h a n lime and magnesia were given. Re,d clover was used as a measure of plant growth. Thc seeding was made in the middle of April and thc pots were exposcd, b u t protectcd from unfavorahle mreather. Distilled water was supplied almost daily.
TABLEI---~OMPARISONS 01 SOLUBILITIES OF ?i~ai.u Caoulio M ~ N S B A L C A a ~ o ~AND ~ t SLLCC~(TES ~ s O P CALCIDM .AND MAUNBSIUM L X CARBONATED WAIRR-PERTOD or( CONTACI(. 4 Hauas GROWTH OF CLOVER RESULTING FROM TREATMENTS Alka- 0.SiOi per 1. Cc. N / l n linity in filfraie of From repeated scedings upon the two soils, we were acid to g. C e c a Csrhonated SUBSTANCO neutralize per hter HIO unable t o obtain any growth in t h e check pots. wo~~hstonite (casior)-in g.. . . . . . . . . . . 5 4 . 2 0.542 0.0566 ~ 0 . 0t ~ i (Caco,)-In ~ #.. . . ~, . . . , . . . .~. 0.900~ ~ ~ The comparison between t h e crops of treatments A , serpentine iMgsio.)-in 8 . . . . . . . . . . . . . 2 1 . 6 0.216 o.oi62 Table 11, and those of F is very striking for both soils. it^ (Msco,)-rn,s.. . . . . . .. . , , . . 2 8 . 0 0.280 mo~~ritonite end reipentin-in each. 6'1.15 0.6935 n.os4o I t should be emphasized t h a t the amount of MgO applied 0.0020 Precipjtsted chalk (CKOz)-lO g.. . , . , . 1 1 7 . 3 I . 173 0.0256 Pp~d.chalkaod~erpenfine-lOg.e*ch.. 121.2 1.212 'rABLe II-T~Z~TMZ~PS .. 92.2 0.922 wo~~ertonite--20 g..,. . . . . . . . . . , , . . . . . Each substance lar mixture) listed below was added in the ?mount equivalent to 16070 Ibr. per acre in excess of the Veltch method,ndlcatmn. the silica fourid in solution would account for b u t a A-MgSiOi D-CaSiO, B-MgSiOr and CaSiO, E--CaCOs small part of t h e CaO and the MgO as dissolved C-MgSiOa and CaCOs F-MgCOa Checks received no treatment.
silicates, even assuming t h a t the bases were combined as silicates with t h e SiOz found, instead of its occurring as hydrate S O , . The same has been found t o be true of the drainage waters from soils devoid of carbonates.
P I , A N OF EXPERIMEFTS WITII CALCIUM A N D M A G N E S I U M SILICATES
These observations, together with the fact t h a t not only silicates h u t pure SiOz will decompose calcium a n d magnesium carbonates and t h a t the affinity of MgO for 3 0 %and TiOl is so great as t o prevent t h e occurrence of magnesium carbonate as a solid in soils,' suggested a comparison between the silicates of calcium and magnesium, a n d t h e carbonates of t h e t w o elenients. The two soils used in the work were a silty loam of "rotten" limestone origin and a s a n d y clay loam. Both soils were low in total lime and devoid of carbonates; and each had a lime requirement of about T ton of calcium carbonate per 3,500,ooo lbs. of soil. The sandy loam contains a considerable quantity of red clay and was apparently benefited physically t o a much greater extent t h a n the silty soil, which h a d a decided tendency t o hake. I n other basket work upon t h e same soils the Veitch method had been used as a hasis of CaO and MgO treatments without cropping. In one set of treatments in this previous work, CaO and MgO were applied separately, in amounts chemically equivalent to 16070 lbs. of CaC03 per 3,500,000 lhs. of soil in excess of t h e indication of the Veitch method, both CaO and MgO being supplied as c. P. precipitated carbonates. I t was found, however, t h a t prior t o t h e seeding of clover, the MgCOs had been entirely decomposed with dissipation of the CO,, hence t h e treatments i n the magnesium carbonate pots were equivalent t o finely divided magnesium silicate. I n t h e silicate treatments the CaO and MgO treatments were duplicated as to amounts of CaO and MgO, hut analyzed roo mesh native mineral silicates, wollastonite and serpentine, were used as sourccs of calcium and magnesium, The treatments werc thoroughly mixed throughout the entire soil mass. Eightinch clay pots, painted inside and out with black asphaltum paint, were used as containers, two pots being used for each treatment and as a check on each 1
Lo
