I 004
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
V h . 6, No.
IP
THE STRENGTH OF NITRIC ACID, PERIOD OF EXTRACTION, AND IGNITION AS AFFECTING THE GRAVIMETRIC DETERMINATION OF PHOSPHORIC ACID IN SOILS
hours, then rotated one half hour again. Pagnoull digested for two hours. The official method of t h e U. S. Dept. of Agriculture' is t o add t h e "01 and evaporate t o dryness. Passernini3 boiled on t h e sand b a t h By 0. t.BRAUER for I hour. Received September 1, 1914 The second part of this investigation is t o determine T h e question of a good measure of the available t h e minimum time for the extraction of the soluble phosphorus in soils has long confronted chemists. phosphates. Fraps4 found t h a t ignition increased t h e T h e earlier investigators thought t h a t b y taking a solu- phosphate soluble in N / 5 HC1 in both soils and phostion of approximately t h e same strength as the plant phate materials. L i ~ m a n ,however, ~ found t h a t igacids they ought to get a correct estimate of the avail- nition decreased the phosphoric acid in soils which are ablq phosphoric acid. I n Europe, Dyer's1 method of soluble in nitric acid. I per cent citric acid was extensively used, while t h e The third part of this investigation includes a study American chemists used N / 2 0 0 HC1. Veitch2 extracted of t h e effect of ignition on t h e amount of P205 set free soil first with water a n d then with citric acid. Max- by extraction with "03. well3 used I per cent aspartic acid. As was pointed out SOILS usm-The soil was powdered up and passed b y Hall4 other factors entered into t h e determination, through a 0.5 mm. sieve, and thoroughly mixed. giving discordant results. Dargastb had already shown Three soils of quite different Pz06content were selected. t h a t t h e amount of phosphoric acid varied very much I - A very rich, black, fine, silty loam, rich in phoswith t h e solvent. For a given soil he got the following phoric acid and humus from Arroyo Grande, San Luis results, in percentages: Aqua regia, 0.108; ammonium Obispo County, California. oxalate, 0 . 0 5 6 ; ammonium citrate, 0 . 0 4 2 ; acetic acid, 2-A light, sandy loam, of fairly good humus and 0 . 0 1 8 ; saturated Cog, 0.015; and distilled water, 0 . 0 1 2 . P 2 0 ~content, from Anaheim, Orange County, CaliMoreover, i t was shown t h a t a given method might fornia. show low PZO6 in a soil which would still show a good 3-Heavy black adobe soil, low in humus and phoscrop yield. This led t o t h e conclusion t h a t a weak phoric acid, from Porterville, California. acid does not get all of the soluble phosphates. Wooda METHOD-weigh out 3 g. of air-dry soil and extract showed t h a t strong "01 removed much more P z O ~ with H N 0 3 on the steam bath. Filter and wash until t h a n the weaker acids; for example, strong "01 ex- washings give no acid reaction. Evaporate t o dryness tracted from the soil 0.23 per cent; I per cent citric, and heat residue a t 130' C. for 2 hours. Extract with 0.08 per cent; I per cent citric in excess of enough t o 20 cc. H N 0 3 (sp. gr. 1 . 2 ) . Filter and wash with warm neutralize the lime, 0.085 per cent PZO5. Other things water until the washings give no test for Ca3(P04)2. being equal, the crop yield showed general agreement Add N H 4 0 H until a precipitate remains and dissolve with the amount of P205 determined by analysis, when in a couple of drops of "03. Warm and add amt h e strong acids were used. monium molybdate and stand a t jo-60' for 1 2 hours. Still there is considerable diversity in the strengths Filter and wash with solution of NH4N03 in "03. of acids used for extraction. Passernini' used concen- Dissolve in NHIOH and slowly add magnesia mixture trated "03, Williams* used HC1 (sp. gr. I . I I ~ ) and , t o slight excess and stand over night. Filter and wash Frapsg used N / 5 HC1. I n 1 8 8 0 Professor Karl free from chlorides with a solution of I vol. IL"4OH, Schmidt showed t h a t the amount of P z O j extracted I vol. alcohol and 3 vol. H'O. Dry in air bath and carevaried with the strength of HCl employed. With I O fully ignite t o constant weight. per cent hot HC1 he got 0 . 5 6 2 ; with 5 per cent cold HC1 S T R E N G T H O F NITRIC ACID-Samples of No. I were 0.09; with I per cent cold HC10.084, in a soil containing extracted with 5 0 cc. HNOI and the rest with 2 0 CC. 1.97 per cent total PzOs. The first part of the present TABLEI-STRENGTHS OF ACID VARIED Per cent Pgos found in soil investigation is t o determine t h e strength of H N 0 3 Strength of acid No. 1 No. 2 No. 3 necessary t o obtain all t h e s o l ~ b l ephosphoric acid, or 15 N . . . . . . . . . . . . . . . . . 0.517 .. .. .. .. 0.067 t h a t included by Hilgard under the term "reserve" 8 N . . . . . . . . . . . . . . . . . . . 0.5ia .... 4 N . . . . . . . . . . . . . . . . . 0.501 0.177 0,065 material. 2 N . . . . . . . . . . . . . . . . . 0,517 0.187 0.074 N 0.154 0.059 ... . . . . . . . . . . . . . . . . 0.516 Not only in the case of strength of acid used in the N . . . . . . . . . . . . . . . . . 0.488 0.155 None extraction is there great diversity of practice among chemists, b u t also in the length of time used in extrac- H N 0 3 . They were all heated for two days on t h e tion. WilliamslO used concentrated HCl a t t h e tem- steam b a t h , with a watch glass over t h e soil cup t o perature of boiling water for ten hours. Sigmon'l prevent evaporation of t h e liquid. The percentages rotated for one-half hour and allowed t o stand for 16 given are computed t o the air-dry basis and are averTrans. Lond. Chem. Sac., 65 (1894). 115. J . A m . Chem. SOC.,21, 1090. 8 Ibid., 21, 415. 4 Trans. J . Chem. Soc., 39, 205. 8 A n n . Agran., 9, 470. 8 J . Chem. SOC.,69, 291. 7 J . Chem. SOC.Abs., 1911, p. 535. 0 U. S. Dept. Agr., BUZZ. 43, 387. THISJOURNAL, 5, 416. 3 10 J . A m . Chcm. Sac., 17, 925. 11 Ibid.. 29, 929. 1 2
@
ages of three checks on sample No. I , and two in t h e other cases, which, with the exception of three instances, did not differ by more t h a n 0 . 0 1 per cent. From Table I i t appears t h a t 2N " 0 3 will give A n n . Apron., 25, 554. Div. of Chem.. Bull. 43, 387. a Chem. Abs. [2],1911, p. 535. 4 Fraps, THISJOURNAL, 5, 416. 6 C. B. Lipman, Ibid.. 4, 663 1 2
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 ENGINEERING C H E M I S T R Y
as much soluble phosphoric acid as any stronger solution. The normal acid shows a slight decrease in yield in t h e second and third soils, and 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 they introduce certain difficulties by bringing down larger quantities of iron and aluminum. PERIOD O F ExTRAcTIoN-In each case 20 cc. of normal acid were used, and the per cent of Pz06 given is an 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 and sufficient for all cases. Passernini boiled for I hour, which is about enough, b u t Williams boiled on t h e water bath for I O hours, which was much longer t h a n necessary. Pagnoul digested for two hours, which was about 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 two show appreciable decreases in the amounts of P z O extracted, ~ as the period of ignition lengthens and as between ignition and 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
The amount of calcium carbonate in soils has long been considered a very important 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 and lime requirements, which indicate need of carbonates-are diametrically opposite, and 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 and 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. The work of Marr2 and 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, and 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 and t o expel from solution t h e liberated , COZ. The more recent work of t h e writers3 has demonstrated t h a t phosphoric acid is less active t h a n hydrochloric acid upon soil organic matter and t h a t I : 1 5 HaPo4 will liberate and 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 and t h e carbonates from this treatment are entirely liberated by I : I j &Po4 with suction and without heat. The Association of Official Agricultural Chemists has recognized the incorrectness of its method and 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 and 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, and 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 and 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
