PHOSPHORIC ACID I N SOILS
929
sugars showed that the amount of lead was so slight as to account for only 0.044 and 0.042 cc. respectively, amounts too small to affect appreciably the polariscopic reading, even in these samples of the lowest grades. I n high grade sugars, which constitute by far the greater portion of the world’s supply, the dilution is correspondingly small and insignificant. I t will thus be seen that these authors are in the unfortunate position of having explained away twice as much difference as ever exists, and that by indirect methods; while the most direct possible methods thoroughly demonstrate the fallacies of their claims and the superiority of the dry defecation over the process heretofore in use. YOSKERS.N.Y.
CHEMICAL METHOD FOR THE DETERMINATION OF THE AVAILABLE PHOSPHORIC ACID IN SOILS. BY A L E H I t S D E ‘ S I G M O X n . Received February 9, 190;.
Though the first steps in Agricultural Sciences were based upon the chemical analysis of soils, there is still a need of methods, for the determination of available plant food in soils. T h e ingredient most needed in hungarian soils is undoubtedly phosphoric acid. T h e author, as chemist of the H u n g a r i a n Slate E x p e r i m e n t Statioit of Plant Industry in Mag3Iar Ovhr: H u n g a r y , has studied this problem during more than seven years, and has devised a method, by which he has tested nearly 100 different soils of Hungary, having made control fertilizer experiments on the same soils. T h e work of the author was rewarded by the prize of the H u n g a r i a n Academy of- Sciences in Budapesl, H u n g a r y , and published recently’ by the same scientific institute. T h e author here gives a brief report of this work, and a complete description of his method for the determinatioq of the available phosphoric acid in soils. T h e starting point of his investigations v a s , to find a nafuraC limit in the solubility of the phosphoric acid in soils. In 1899 T h . Schlosing, jzm. in France, published some of his experiments, which seemed to divide the phosphoric acid in the soil into two distinct parts, the slightly soluble and less soluble part of phosphoric acid’. Schlasing tested but four different soils, and the author has repeated the experiments of Schlosing on eleven different Hungarian soils. T h e experiments of both authors agree in so far, that there is a distinct point which separates the phosphoric acid of soils in the above mentioned two parts. When we start with distilled water, and increase gradually Mathematikai 6s Tenneszettudoniftnyi Kijzlernenyek XXIX, No. I. 1906. A konnyen fttsajAtithat6 phosphorsav jelentosege 6s “tneghatArozftsa talajaink trftgyasziiksegleteiiek niegftllapitftsa czeljQb6l.”-Dr. Sigmond Elek. Compt. rend., 128, 1004. Action des liqueurs acides tres entendues sur le phosphates du sol.-Th. Schlosing fils. 1899. Paris.
930
A L E S I I ’ S Dl2
SII;>lVIONI)
the acidity of the soil solution by adding more aud inore nitric acid to the water, and determine the acidity of the soil solution and the amount of phoshoric acid dissolved in the solutioii they both have found, that o n increasing the end acidibi o f t h e soliLtion, iliirc is a rapid increase in tllc a m o u n t of soluble phosphoric acid also. But a t the point, wlieu the end acidity of the solution reaches 2 0 0 nig. S,O, per liter, on further increasing the end acidity to 1000mg. N,O, per liter, there is PiTartically ?tof k r f h e r increase in t h e anzouitt of phosphoric acid in the solution. And this seems to be a nafuraldivision of the Phosphates of the soil into the easib1 soluble a d less solubCe p a i f , for after the second limit is reached the amount of phosphoric acid dissolviiig, on increasing the end acidity of the solution, increases very rapidly again. T h e data of Tables I aud I1 illustrate the rule just mentioned. For the graphical demonstration of the geueral rule, drawn from the above data the author coiistructed the following average diagram.
According to this diagram the straight part a-6 of the curve represents the level, which divides the phosphates i i i the soil into two natural and distinct parts, the easily and slowly soluble parts. T h e next problem to study was, to find out if there is some relation between the availability aud the amount of the easily soluble phosphoric acid in soils. To solve this question, the author collected by the help of the Ex,beriment Station of P l a n t Indiisfry a t M a g y a r Ovciv, H u n g a r y , nearly 100 different Hungarian soils, one part of which was tested by field experiments, the other by pot experiments and some of them by both i. e. field and pot experiments. T h e most of the pot experiments were carried out with the complete variation of the three chief plant foods, N . P. K., and each experiment repeated three or four times. According to this, there were made about 24-32 pot experiments with each soil; in all there were tested 51 soils by pot experiments and there were made about I 200-1600 pot experiments. On the other hand sj soils were tested in fields, 1 2 being the same tested also by the pot experiments. I n all 94 soils were tested by fertilizing
931
PHOSPHORIC A C I D I N SOILS
TABLEI. N.zOs mg. End acidity P205m g in used for the ofthe SOIU- I liter of t h e solution tion N200mg. solution 1. Coiiporay, loamy soil 0 -25.0 0.38 25
-I
50 I00 203
300 400 5*
1.9 3.5 9.9 69.3 148.5 245.0
354.0 1090.o 1990.0
I220 2220
NzO mg. R i i d acidity P9,0Pa mg. in used for the of the solu- I liter of the solution tion N205nig. solution 2. Neauphle. loamy soil
I .07 1.66 1.89 I .97 1.79 1.92 1.95 3.89
2260
5260 10260
20260 3. Toinville, sandy soil j $ CaCO, 0 250
500 750
-64. -95.6 -20
1500
58.0 285.5 j29.0 766.5
r750
1023.0
2000'
2500
124s. 1793.
5-
4310.
Io00 I 250
10000
4.
9212.
1.72 3.33 4.42 4.82 4.94 4 47 4,97 5 16 5.23 5.59 6.31
20.0
72.0 262.0 515.0 956.0 1844.0 4780.0 9630.0 19300.0
0.74 2.74 3.64 3.4r 3.63
. ..
3.71 4.65 6.60 8.70 10.49
Boulogne, soil very rich in CaC03 0
0.5 1 2
-30.5 - 5.0
0
90 I so 2 70 520 77 0 I 260
0.52
50 IO0
203
- 60. 16. - 164. -229.
-I
500
-3jS.
Io00
-404.
2500 3000 3100
-23s.
3200
3300 3400 3600 3800 4000
-
s4.
6. 18.6 57. 124.
3'9. 416. 632.
0.61
0.54
. ..
1.46 2.63 4.34 8.F 11.30 13.00
14.19 14.75 17.06 17.42 17.97 17.59
TABLEI1 Name and ph sical character of txe soil
Per cent. CaCO,
P? Bashaloni (loam)
Hailsag (peaty soil)
Leva (clay) KaIocsa (loani ) 22.91 Pa
Acidil r of the solution calcu- In z j g . lated in mg. N ? O per ~ liter soil sample at t h e b e a t the nig. P,Oj ginning end
65S.8 1182.6 1463.0 2959.2 658.8 I 182.6 1463.0 1738.8 2959.2 745.2 1441.8 2959.2 6jS.8 1463 o ssg1.0
6339.6 6998.4 745.2
Po6 (loam ) 3.11
1441.8
1738.8 2959.2
+-
16.2
f 313.2
626.0 1987.0 - 108. - 415. - 67j. - 896.
T
-t 2052.
- 567. tr193. i2743. - 156.6 - 86.4 neutral 635.4 - 637.2 - 54.0 199.8 - 367.2
f
-
1485.0
4.6 6.0 6. o 8.0 2.4
6.2 5.6 7.3 8.6 3.2 3.2 4.5
..
.. .. 20.5 21.1
traces I 1.3 18.7 20.5
Per cent soluble P20j
0.018 0.024 0.024.
0.032 0.010 0.025
0.022
0.029 0.034 0.013 0.013 0.018
. ... . .. . .., *
0.082 0.084
. ...
0.045
0.075 0.082
932
ALEXIUS LIB ' S I G ~ I O S D
experiments, and tlie saiiie samples were also tested by the chemical method of the author. T h i s method corisists of the following determinatioiis: I. l h DefermiitatiJii o f t h e BasiciQ o/ f h e Soi/.--Titratiiig 2 j grams of soil with a standard solutioii of nitric acid, coiitaiuing I O O mg. S,05 per liter, and boiling the soil, to drive out all tlie carbonic acid, we get a t the basicity of the soil, that is theamozmt cfzz'fi7'c a r i d uezitmlizrd b y the soil. T h e author uses the term basicity for the nuniber of nig. S,Oi for complete neutralization of 2 j g. of the soil. TVeigh 2j g. air dried soil in a beaker, add a siiiall amount of water and I O cc. of the standard nitric acid solution. Then boil tlie solution until the carbonic acid escapes, test, with 1it:nus paper, and if' the renction is uot distinctly acid, add again I O cc. of nitric acid, boil, and test again with litmus paper. Repeat this until there is a distinct excess of acid. Then pour tlie whole contents of tlie beaker into a standard flask of joo cc., fill up, shake, filter and determine in j o cc. tlie excess of acid with a standard solution of potassium hydroxide such that I cc. neutral13y calculating the izes I O nig. X,O,. Use methyl orange as indicator. number of mg. of N,O, neutralized by 2 j g. of soil, -se get the basicity of the soil. With soils, which on adding some acid effervesce distinctly, the author has fouud it better to use only 5 g. instead of 2j g. 2. tlfafiiizf of the Soil Sol?~tion.-In making the soil solution, me wish to get a solution with an end acidity ranging zoo-1000ing. S,O., per liter of the soil solutioii. T h e eizd acidif)! means the acidity of the soil solution after the solution is ready for the deteriiiination of phosphoric acid. From the basicity of the soil, we car1 nearly calculate the amount of standard acid wanted, for the soil solution. Xaniely: If the soil contains practically no traces of Carbonates, or the I. basicity runs below t h e value of 1000 nig. S20j:use but I O cc. of the standard nitric acid solution to 2 j g. of soil. If the soil contains carbonates, but the basicity ranges but IOOO2. 4000 ing. S,O,: use just as inany cc. of the standard acid a s are required for the full neutralization of t h e basicity of the soil to 2j g . of soil. 3. If the soil is very much loaded with carbonates or the basicity runs above 4000 mg. S,O,, and t h e soil is almost loamy or clay, use 5-10 cc. less of the standard acid than would be required for t h e complete neutralBut in the case of sandy and loose, peaty soils, ization of the basicity. the author has found it best to use the amount of acid according to 2 . N o w for making the soil solution weigh 2 5 g. of air dried soil in a standard flask of one liter, add about I O O cc. distilled water and standard nitric acid according to the above detailed rules. With soils rich in carbonates, take care of the effervescence; then fill up to 1000cc., close the
933
PHOSPHORIC ACID Ih' SOILS
flask and put it in a rotatory apparatus. After half an hour of slow rotation (one rotation lasting about one-half minute) take out t h e flask, carefully remove the stopper and allow t h e solution to stand at room temfor about 16 hours, Then put the flask again in the perature (12'-23') apparatus and rotate one half of an hour again. Xow filter the solution aud take 25 cc. for the determination of the end acidity of the solution. T h i s is done by titrating it with the above mentioned standard potash solution, using methyl orange as indicator, If the end acidity would not fall between the 200-1000 mg. N,Oj as wanted, repeat the preparation of the solution according to the results of the end acidity. If the end acidity is right, the solution is ready for the determination of phosphoric acid. of Phosjhoric Acid iz the Solution.-Evaporate -3. The Determinafio~~ 800 cc. of the filtered solution to about j o cc. using a small amount of a 2 0 per cent. amnioniurn nitrate solution, for the precipitation of silicic acid. When the solution is evaporated as far as about roo cc., filter, add jo-100 cc. ammonium molybdate solution, heat gently until t h e precipitation is complete, filter the solution, wash the precipitate with some nitric acid of 5 per cent. , dissolve the molybdate precipitate with ammonia, add hydrochloric acid in excess, and again ammonia in excess, and precipitate with the usual magnesia mixture. T h e small amount of magnesium phosphate precipitates sometimes very slowly and 48 hours should be allowed for complete precipitation. Dry and burn the filter paper in a platinum crucible, ignite, and weigh the magnesium pyrophosphate a s usual. T h e amount of P,O, found, multiplied by 5 , gives the per cent. in the soil. This is exactly the method used by the author in his studies. T h e exactness of t h e method may be shown by the data of the following Table 111. TABLE111.
End acidity of Kame of the soil
.............. ................. ..... ........ .............. .............
the solution a. b.
Tolna o Pel -150 Puszta-Somorja - 10.8 XI-OvLri akad. - 10.6 kiserleti ter. Vajka - 60 Kisber -430 Nagy-BossLny -320 F-Puszta Als6takarmanyos - 75 KajniBd -220 Vaj ka -320 Mezohegyes -290 M-Ovari akad. -140 kiserletiter Lucsonyi kis6rl. ter (Carlau). -1h FLczlnkert -235 F- Pusztareti tBbla - 21.6 F- Pusztareti tabla -120
...... ....... ............ .............. ........ .........
........... ......... .. ..
0
-150 - 16.2
Gm. P,Os in 800 cc M PO of the solution soiutie tn a. b. a. b.
61;
0.0009 0.0009 0.0015 0.0029
4.5 4.5 0.0015 5 5 16 0.0033 14
- 10.8 0.0047 0.0042 23 - 80 0.0045 0.0047 2 2 0.0052 0.0053 26 -470 -350 0.0054 0.0055 27 - 75
0.0066 0.0066 33 . . 0.0066 0.0068 33 0.0068 0 . 0 ~ 6 6 34
22 22.5
27
27 33 33.5 33.5 55 56
0.0109
0.0113 54
-130
O.OIII
o.orr5 55
57
-240 -240
0.0113 0.0119 56 0.0152 0.0153 76 0.0173 0.017 1 86
59 77 85
122
123
-400 -280
- 27.6 -130
0.0245
0.0246
4.5 5 15
21 23 26
33 34 33 56
-210
;!
