T H E J O L T R N d L OF I N D I T S T R I A L ALVD E N G I N E E R I N G C H E M I S T R Y
July, 1914
577
TABLEPERCENTAGE COMPOSITION OF SOIL SEPARATES No. 1 VOLUSIA SILTLOAM Fine CONSTITUEAT sands Si02 . . . . . . . . . . . . . . . . 9 0 . 0 5 1.89 5.08 0.64 CaO . . . . . . . . , , . . . . . . 0.56 Trace Zr0z . . . . . . . . . . . . . . . 0 . 1 4 NazO. . . . . . . . . . . . . , . 0.79 . KaO . . . . . . . . . . . . . . . , 0.99 PzOa . . . . . . . . . . . , . . . . 0.16
No. 2
CECILSANDY LOAM .-Fine -. Coarse Fine silt Coarse Fine silt silt a n d c l a y 87.78 4 6 . 0 9 1.69 10.51 5 . 6 6 22.52 0.95 0.98 0.47 0.70 0.15 1.03 0.07 0.01 1.06 0.40 1.06 1.66 0.44 0.08
sands 94.79 1.21 2.73 0.87 0.33 Trace 0.11 0.13 0.79 0.10
h’o. 6 YORKSILTLOAM
silt a n d clay 86.89 45.92 1.21 6.46 6.86 28.14 1.05 1.19 0.13 0.26 Trace 0.36 0.06 0.01 0.06 0.20 1.66 1.99 0.12 0.23 No. 7
LOUISA LOAM
r
9 7 . 5 1 75.03 3 8 . 9 7 0.82 2.27 7.13 1.07 15,08 31.33 0.41 0.33 0.45 0.11 0.19 0.36 0 . 0 4 Trace Trace 0.03 0.05 0.02 0.59 0.61 0.06 3.72 5.40 0.22 0.09 0.04 0.12 P205.. . . . . . . . . . . . . . ( a ) Includes both ferric a n d ferrous iron.
.
97.35 1.24 0.92 0.55 0.27 0.06 0.11 Trace 0.02 0.10
89.11 2.79 3.72 2.44 0.34 0.15 0.15 0.24 0.76 0.01
57.07 7.11 18.51 1.70 0.22 0.26 0.04 0.14 1.85 0.24
TABLE 11-AVERAGE, MAXIMUM A N D MINIMUM AMOUNTSO F THE SEVERAL MINERAL CONSTITUEKTS FOUND I N THE DIFFERENT SEPARATES
{$ax. Min Av. Fez03 Max. iMin.
AlzOa Ti02
{A v’ Max. Min. Av. ihlax. (Min.
ikx.
CaO
Min.
PERCEATAGES Fine silt Fine Coarse a n d sands silt clay Constituent 8 8 . 5 0 83.05 45.52 Av. 9 8 . 9 9 95.37 5 8 . 7 1 hIgO Max. 76.23 6 4 . 1 3 22.55 Min. 1.66 1.96 8.73 2.95 4 80 17.02 ZrOz Max. 0.35 0.52 3.97 Min. 5.48 8 44 22.57 \Av. 12 56 18 28 31.33 NazO Max. 0 . 4 0 1 48 1 6 . 7 6 IMin. 0.72 1.11 1.34 /Av. 1.20 2.44 3.38 Kz0 iMax. 0.41 0.33 0.45 ( Min. 0.59 0 . 4 8 0.64 \Av. 1 . 7 2 0 . 9 7 1.27 PzOs Max. 0.05 0.13 0.22 IMin.
{ jAV’
Fine Coarse sands silt 0.40 0.33 2 . 0 6 1.05 Trace Trace 0.05) 0.11 0.14 0.20 0.02 0 . 0 3 0.73 0.86 2 . 1 8 1.78 Trace 0 . 0 6 1.58 2.04 5 . 5 6 4.35 Trace 0 . 7 6 0 . 1 1 0.08 0.20 0.14 0.04 0.01
Fine silt and clay 0.54 1.56 Trace 0.02 0.07 0.01 0.35 0.61 0.14 2.15 5.40 0.63 0.29 0.46 0.08
Table I1 of averages a n d maximum a n d minimum results shows t h e general composition of t h e finer separates of loams and direction of segregation of constituents in them. BUREAUOF S O I L S
E.
s. DEPARTXENT O F AGRICULTURE %’ASHIXGTON
THE PREPARATION OF “NEUTRAL” AMMONIUM CITRATE’ By
ERMON D. EASTMAX AND
No. 4 HAGERSTOWA LOAM
JOEL H. HILDEBXAND
I n t h e official method for t h e determination of phosphoric acid i n fertilizer, i t is necessary t o use a “neutral solution’’ of ammonium citrate of density 1.09 a t zoo. A number of methods have been proposed for preparing this solution, such as those using various indicators,* t h e titration b y c o n d ~ c t i v i t yt,h~e extraction a n d heat of reaction method^,^ a n d a n analytical method proposed b y P a t t e n a n d MartiS6 Mention 1 Presented a t t h e 49th Meeting of the A. C. S., Cincinnati, April 4-6, 1914. 2 Bull. Bur. Chem., 107, 1; 132, 11. 8 Hall and Bell, J . A m . Chem., SOC.. 4 (1912), 443. Bell and Cowell, J . A m . Chem. Soc., 35 (1913), 49. THIS JOURNAL, 5 (1913), 567.
No. 5 NORFOLK SANDY LOAM
.?
Fine Coarse Fine silt sands silt and clay 98.99 9 5 . 3 7 58.71 0.35 0.52 3.Y7 0.40 1 . 4 8 18.44 0.57 1.12 3.38 0.05 0.24 0.28 0.01 0 . 0 3 Trace 0.06 0.18 0.07 Trace 0.08 0.26 Trace 0.15 0.63 0.08 0.03 0.08
Fine Coarse Fine silt sands silt a n d clay 7 9 . 4 4 80.53 55.29 1.27 1.05 4.84 11.39 10.08 24.80 0.79 1.11 1.86 0.88 0.68 0.43 Trace Trace Trace 0.14 0.03 0.20 0.24 1.58 1.31 1.62 5.56 4.35 0.12 0.14 0.17
Fine Coarse Fine silt sands silt and clay 76.23 8 2 . 2 6 42.96 2.32 1 . 6 7 11.13 8.01 8.19 23.80 1.03 1.16 1.01 1.27 1.72 0.97 1.44 2.06 0.84 0.11 0.11 0.01 0.27 0.83 0.37 3.83 2.54 2.02 0.45 0.20 0.03
XO. 8 PENNSILTLOAM
No. 9 GLOUCESTER STONY LOAM . r
(with one exception) increase in percentage composition with t h e fineness of t h e particles. Lime, magnesia a n d soda seem t o follow no general rule. The higher content of potash in t h e coarser separates of three soils is due t o t h e presence of coarse crystals of potash feldspar. As a rule potash is segregated i n t h e finer particles.
Constituent
.-
1 7 -
SiOi.. -~~~ , . . . . . . . . . . . . . FezOs. . . . . . . . , . . . . . . Alz03. . . . . . . , . . . . . . . Ti02 . . . . . . . , . . . . . . . CaO. . . . . . , . . . . . . . . . AlgO. . . . . . , , , . . , . . . ZrOz. . . . . . . . . . . . . . . NazO. . . . . . . . . . . . . . . Kz0. . . . . . . , . . . . . . . .
SiOz
NO. 3 DURHAM SANDY LOAM
85.16 2.46 7.52 0.70 0.31 0.35 0.08 2.18 0.58 0.06
84.27 46.05 1 . 8 1 10.09 8.11 23.23 1.14 1.04 0.35 0.98 0.40 1.56 0.11 0.01 1.78 0.41 1.38 2.87 0.02 0.29
.
77.19 6 4 . 1 3 22.55 2.95 4.80 17.02 12.56 1 8 . 2 8 16.76 1.09 1.20 1.15 1.09 0.78 0.74 0.30 0.62 1.05 0.01 0.09 0.08 0.49 1.70 1.52 1.79 1.40 2.60 0.43 0.15 0.13
ivo. 10
CARRINGTOA LOAM
-_
I
88.33 2.07 5.15 0.45 0.59 0.28 0.07 0.56 2.40 0.10
8 5 . 0 4 41.62 1.80 9.02 6 . 9 1 18.14 0.69 0.68 0.67 1.20 0.37 1.21 0.07 0.01 1.12 0.36 2.22 1.67 0.04 0.46
should also be made of t h e recent paper b y Rudnick a n d Latshaw.’ The result has been t h a t while one analyst can usually reproduce his own results, t h e results of different analysts have frequently shown wide variations. Thus LIcCandless,2 while referee on phosphoric acid for t h e Association of Official Agricultural Chemists, found solutions made b y differe n t men t o vary in their ratio of ammonia t o citric acid from I : 3.775 t o I : 4.189. The commercial importance of this solution requires t h a t i t should be defined accurately a n d t h a t t h e method for i t s preparation should be simple a n d reliable. Reference t o this problem b y one of us in a n address3 a t t h e Milwaukee meeting of t h e American Chemical Society led t b a request from t h e Fertilizer Division for cooperation i n its solution, resulting i n t h e work which is described i n t h e following pages. DEFIKITIOK
OF A “NEUTRAL
SOLUTION”
I n defining t h e solution it is necessary t o bear i n mind t h e fact t h a t salts of weak acids a n d bases do not necessarily react neutral i n aqueous solution. A saltlike sodium acetate will react alkaline, due t o hydrolysis, while one like ammonium chloride will react acid. When both a weak acid and a weak base are involved as with ammonium acetate, considerable hydrolysis will take place, a n d t h e solution will contain a n appreciable quantity of free acid a n d base, though t h e extent t o which t h e solution would depart from neutrality would depend on t h e relative strength of t h e acid a n d base. A solution of ammonium citrate, therefore, shows considerable hydrolysis, a n d contains free acid a n d free base, even when t h e citric acid and t h e ammonia are present i n equivalent quantities. For this reason i t is folly t o expect t o prepare a neutral solution of ammonium citrate b y one of t h e methods t h a t has been proposed, i. e., t o a d d a n excess of ammonia a n d let stand till t h e excess has volatilized. Any solution of ammonium citrate, whether acid or alkaline, contains free ammonia, which would be gradually removed on standing open t o t h e air a n d more rapidly b y boiling. 1
THISJOURNAL, 5 (1913). 998
2
Bull Buy. Chem., 122, 147. Hildebrand, J . A m Chcm. SOC.,36 (1913). 848, 1538.
3
T H E J O U R N A L OF INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
578
Whether or not a solution containing equivalent amounts of ammonia a n d citric acid, which we shall call the normal salt, will be neutral, acid, or alkaline, depends upon the relative affinity of ammonium ion a n d citrate ion for hydroxyl a n d hydrogen ion, respectively, of water; in other words, upon t h e relative ionization of NH40H a n d HCOHsO,--. Since t h e dissociation constants of the three hydrogen ions of t h e citric acid molecule are not known separately, t h e question of t h e neutrality of the solution must be determined experimentally. This is very conveniently done b y means of t h e hydrogen electrode, as previously described b y one of US.^ T h e results of such titration in t h e neighborhood of t h e neutral point are shown
t h e former results from t h e analytical a n d conductivity methods rather t h a n the latter, i t will doubtless be less disturbing t o present practice to recommend it rather t h a n the truly neutral solution. If desired, t h e procedure we here recommend could easily undergo the slight modification necessary t o yield t h e neutral solution. We therefore define t h e solution as one containing equivalent quantities of citric acid a n d ammonia, a n d a d d t h a t a hydrogen electrode immersed in it will show a n E. M. F. against a normal calomel electrode of 0.71 volt, from ayhich t h e hydrogen ion concentration is calculated t o be IO-^.^. PRIKCIPLES O F PROPOSED METHOD
solution of ammonium citrate of equivalent acid a n d base content would be t o use t h e hydrogen electrode in the form such as was described b y one of US.^ T h e whole curve would not need t o be obtained. It would suffice t o set the opposing E. M. F. a t 0 . 7 1 volt a n d a d d ammonia until the galvanometer or electrometer just deflected in the opposite direction on pressing t h e key. This would require the apparatus described for such purposes, which would entail some expense, although it would prove a useful addition to a n analytical laboratory. Since this is too much t o expect, however, we have devised a method whereby the same result may be achieved by the use of a n indicator with a slightly greater expenditure of time a n d labor. T h e comparatively slight change in hydrogen ion concentration between a solution containing a n excess of acid a n d one containing a n excess of ammonia, showing itself in t h e not very rapid rise in t h e curve, makes clear the reason for t h e unsatisfactory behavior of indicators in this titration. Most indicators require a change in hydrogen ion concentration of nearly a power of ten in order t h a t their colors may be entirely changed. Within t h a t range some color standard is necessary for comparable results a n d this makes t h e results very subjective, as ordinarily worked. ( B y reference t o Fig. IV of the paper on the hydrogen electrode, t o which frequent reference has been made, it will be a t once evident t h a t t h e hydrogen ion concentration of sodium citrate changes far more rapidly through t h e neutral point t h a n t h a t of ammonium citrate, sd t h a t the former gives a sharp end point with a n indicator while t h e latter does not.) I n order t o fix t h e hydrogen ion concentration of the solution accurately i t is necessary t o choose a n indicator whose color change is a maximum a t the desired point, a n d then t o fix the desired color by means of a standard solution which will give t o the indicator t h e same color t h a t it would get in a solution of t h e normal ammonium citrate of the prescribed density. It was found t h a t a standard solution of the same hydrogen ion concentration as t h e citrate solution would not give t h e same color with the indicators tried. This is t o be attributed t o the large salt effect of such a concentrated solution. The acidity of the comparison solution h a d therefore t o be adjusted by trial. For the comparison solution we used a mixture of
4 - J - ~ ! - ~
zz FIG. I-HYDROGEN ELECTRODB TITRATION CURVE, CaHsOl
WITH
NHiOH
t h a t t h e point of inflection of such a curve represents t h e normal salt, while E. M. F. of 0.69 volt against a normal calomel electrode, corresponding t o a hydrogen ion concentration of IO-’ a t room temperature indicates a truly neutral solution. ( I n this calculation t h e liquid contact potential has been neglected, as where t w o nearly neutral solutions of high concentration are in contact t h e potential can be disregarded where a n accuracy of a centivolt is sufficient, as is t h e case here.) It will be seen t h a t t h e solution of t h e normal salt is slightly alkaline, having a hydrogen ion concentration of 10-7.4. It, therefore, becomes a question which solution should be selected. It may be noted t h a t t h e acidity varies most rapidly with the composition along this portion of t h e curve, and t h a t solutions containing a definite excess of citric acid or ammonia would not need t o be made nearly as carefully in order t o have a uniform hydrogen ion concentration, and, presumably therefore, a uniform action on phosphoric acid bearing material. Since, however, the neutral solution is prescribed legally, as t h e official method, we will show how it can be made, a n d since t h e normal a n d neutral solutions are so nearly alike, a n d since 1 LOC.
cit. .
Vol. 6 , KO. 7
1 LOC.
Cif.
July. 1914
T H E J O C R - V A L O F I N D U S T R I A L A N D E LVGI X E E RI ATG C H E M I S TI? Y
mono- a n d disodium phosphates. The change from a solution containing t h e ions PO4- - - and HPOd-t o one containing H P 0 4 - - a n d H2P04- is marked b y a sudden increase in hydrogen ion concentration which is shown very satisfactorily b y phenolphthalein. The change from t h e latter pair of ions t o the mixture H2P04- and H3P0, causes another sudden increase
.
579
i t only. Changes would have t o be made i n the standard of comparison if a n y other indicator were employed. P R 0 C E D U R E R E C 0 h.1 M E X D E D
For t h e preparation of citrate solution in two-liter lots, dissolve 3 7 0 grams in I 500 cc. of water: and nearly neutralize with concentrated ammonia solution. Cool t o 2 0 ’ and then a d d more ammonia from a h buret until a I O cc. portion of t h e thoroughly stirred solution, with a suitable quantity of rosolic acid, shows t h e same color in a Nessler t u b e t h a t t h e same amount of indicator gives with a I O cc. portion of a phosphate solution prepared as follows: Titrate a 2 j cc. portion of a n approximately 0 . I molar stock solution of N a 2 H P 0 4 ( t o which dilute HC1 or N a O H has been added until phenolphthalein is just colorless in t h e solution) with N / I O HC1 and methyl orange. T o a fresh 2 5 cc. portion (neutral t o phenolphthalein) a d d of t h e volume of HC1 used in t h e previous titration. Stir well a n d use a suitable portion for t h e color standard above. When the citrate is neutralized. bring t h e solution t o a specific gravity of 1.09 a t 2 0 ’ C. When small quantities are t o be made i t is simpler t o prepare a volume of phosphate equal t o t h e desired volume of citrate, thus avoiding 05 t h e withdrawal of samples. For t h e I O cc. portions two drops (100drops = 3 cc.) of rosolic acid. 0 . 2 ; g r a m dissolved in j o cc. alcohol and j o c c . water, g a m a FIG. 11-TITRATION06 NazHPOI WITH HC1 good color. of acidity indicated very sharply by methyl-orange. The method is sensitive t o about 0.1per cent of t h e Between these points t h e change in acidity is very total “,OH involved. Three distinct samples .of slow, so t h a t small differences in t h e concentrations “neutral” citrate prepared b y t h e above formula, and make but little change in t h e acidity, as shown b y t h e subsequently tested with t h e hydrogen electrode ~ ~ curve in Fig. 11. The difference in t h e end points with showed ( H + ) concentration of IO-^.^^', 1 0 - ~. . and these two indicators, on titrating a solution of disodium hydrogen phosphate, serves t o fix the concentration of phosphate in t h e solution, a n d i t is then easy t o transform a part of this by addition of t h e proper amount of hydrochloricacid,sothata solution of definite hydrogen ion concentration is obtained, subject t o a minimum of variation on account of impurities or errors in t h e manipulation. I n choosing a n indicator, alizarin, guaiacum tincture, neutral red, cryanin, hematein. rosolic acid a n d azolitmus werecompared. Considerations such as t h e sharpness of t h e change a t t h e desired point, t h e nature a n d permanence of the F I G . 111-CONDUCTIVITY AND E. M. F. C U R V E S , TITRATION OF C I T R I C A C I D WITH A M M O N I A colors, a n d t h e adaptability t o t h e standard solution adopted, led t o t h e final IO-^.^^ , respectively, t h e largest error being 0 . I per cent. selection of rosolic acid. T h e figures given apply t o T h e electrode method was finally compared with t h e
8,
I-
. THE 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
j80
conductivity method by a titration in which bridge readings were made simultaneously with E. M. F. readings. The results appear in the curves of Fig. 111, which show satisfactory agreement in the abscissae. SUMMARY
Vol. 6 . No. 7
vegetable ammoniates in commercial fertilizers is a subject of considerable interest a n d importance t o chemists who have charge of analytical work in connection with the enforcement of state fertilizer laws. T h e alkaline and neutral permanganate methods for organic nitrogen activity are now quite generally employed in many control laboratories. When properly interpreted they are capable of making reliable differentiations between high a n d low grade organic ammoniates as regards their activity or availability as nitrogenous plant food. For several years past t h e writers have taken an active interest in these problems both as regards laboratory methods a n d their control by pot experiments. I n connection with these lines of investigation we have endeavored t o secure some satisfactory method for separating quickly the organic nitrogenous portion of commercial fertilizers from the mineral nitrogen, acid phosphate a n d potash salts. Several procedures have been tried b u t with indifferent success. T h e scheme about t o be described was perfected last year a n d employed as extensively as time permitted on many commercial fertilizer a n d crude nitrogenous stock samples.
With the aid of the hydrogen electrode a n indicator method for the preparation of tri-ammonium citrate has been developed.. T h e H + concentration given b y solutions of this salt of 1.09 specific gravity is shown to be IO-'.^. This concentration is obtained in t h e preparation of the citrate by the use of a n easily prepared color standard, made by mixing HC1 a n d NaaHPOl solution. T h e results of a simultaneous determination of the “neutral point” with t h e electrode a n d conductivity methods are shown graphically, a n d t h e r e ’ a r e given results of several trials of the formula suggestcd. xom-It seems very likely t h a t the difficulties of the fertilizer chemist in determining available phosphate are not due entirely t o lack of uniformity in t h e ammonium citrate solution used. I t may be impossible to distinguish sharply between “reverted” a n d “available” phosphate by means of neutral ammonium citrate solution. For example, i t might be found t h a t available phosphate is barely dissolved by a citrate solution METHOD having a hydrogen ion concentration of IO-^: while Prepare the sample by drying from I O O t o 600 reverted phosphate is not greatly affected until a grams of the material, preferably unground, a t a hydrogen ion concentration of IO-^ is reached. Obviously the best solution for extraction would, in t h a t temperature of not over 170’ F. Cool a n d weigh. case, be one whose hydrogen ion concentration is T h e amount taken depends on the nature of t h e material IO-^, and remaiizs so duving the extractioiz. A solution a n d on the quantity of t h e organic portion desired. whose hydrogen ion concentration varied between Nearly fill a suitable beaker with carbon tetrachloride a n d a d d the sample in 2 5 t o 50 gram portions. Stir IO-^ a n d IO-^ would dissolve uncertain amounts of available phosphate. Furthermore, as mentioned in a n d allow t o settle. Skim off the portion t h a t floats t h e above paper, solutions of the normal ammonium . a n d throw on t o a dry filter. A t i n tablespoon is very citrate have a hydrogen ion concentration most sub- serviceable for this purpose. Continue this procedure ject t o variation, while solutions containing a n excess until the entire sample has been thus treated, using of acid or base would be changed much less by a n altera- more carbon tetrachloride a n d another beaker if necestion in the amount of t h a t excess. By reference t o sary. D r y t h e filter containing the organic portion t h e paper b y Hildebrand’ i t will be seen (Fig. IV) t h a t in a n air bath. Cool, weigh a n d preserve for microthe same considerations apply t o t h e proposal to use scopical a n d chemical analysis. T h e bulky residue t h a t sinks is transferred t o a z sodium citrate. The hydrogen ion concentration of liter flask, the filtrate from t h e organic portion is added, a n acid solution would be far less affected t h a n would t h a t of one nearly neutral by small variations in t h e a n d the carbon tetrachloride recovered by distillation a m o u n t of acid present. If a n acid solution will not in, a covered water bath. T h e residue remaining in .sharply differentiate available a n d unavailable phos- t h e flask can be removed easily after final drying in phate, then recourse must doubtless be had t o t h e a n air or vacuum bath a n d is then cooled, weighed and analyzed if desired. a m m o n i u m salt with a n excess of ammonia. I t has been found advisable in many cases to screen It may also be found desirable t o maintain a definite the sample previous t o treatment, through a I mm. hydrogen concentration during t h e digestion b y means sieve a n d make the carbon tetrachloride separation of a suitable indicator, adding ammonia or citric acid on the two portions separately. If t h e odor of the as needed t o maintain a definite color. reagent proves offensive a small exhaust fan placed CHEMICAL LABORATORY o n t h e desk near the beaker with outlet pipe extending ~ I N I V E R S I T YOP C A L I P O R N I A , B E R K E L E Y outside is recommended, or the separation may be made under a hood. W PROCEDURE FOR SEPARATING ORGANIC AMMOT h e following ‘summary shows the behavior of many NIATES FROM THE MINERAL PORTION OF of the materials used in fertilizer manufacture. COMMERCIAL FERTILIZERS2 By C . H . JONESAND G. F. ANDERSON
T h e separation and identification of animal and 1
LOG.c i l .
2 Presented at the 49th Meeting of the .\rnerican Chemical Society, Cincinnati, April 6--10, 1914.
FLOATS O N CARBON TETRACHLORIDE-Dried blood, fish, tankage, hoof meal, horn meal, leather, kanona tankage, morocco clippine, azotin, cottonseed meal, castor meal, castw pomace, beet refuse mmpoand, nitrogenous manure, casein, peat, garbage tankage, tartar pomace. moarah meal, rape meal, soja bean meal, wheat gluten, tobacco stems, fillerine (partly), cinders (rertain types).
.
