ANALYTICAL CHEMISTRY
1066 amount of glucose was increased t o 100 micromoles, it still was not oxidized under these conditions. However, 10 micromoles of oxalic acid decolorized the permanganate.
statistical treatment of the data, and John Ilemp and H. P. Iiato for technical assistance. LITERATURE CITED
RECOVERY OF ACONITIC ACID FROM A PROTElh SOLUTION
cis-ilconitic acid (0.1 micromole) was added to a protein solution and the mixtures were deproteinized by the addition of metaphosphoric acid, final concentration 3%. The suspension was centrifuged and the permanganate-reducing materials of the supernatant solution were determined. The date of Table 111 indicate that complete recovery of the added aconitic acid was obtained. ACKNOWLEDGMENT
The author wishes to thank Lowell Woodbury for aid in the
(1) Anschiitz, R., and Bertram, TT.. B c r ~ 37, , 3967 (1904). (2) Goldblith, S. A,, and Proctor, E. E., J . Bid. Chem., 187, io5
(1950). (3) Kolthoff, I. JL, and Sandell, E. B., "Textbook of Quantitative Inorganic .4nalysis," p . 592, Sew York, Maomillan Co., 1946. (4) Lauer, K., and RIakar, S. 31.,.Is.~L. CHEY.,23, 587 (1951). ( 5 ) JIerz, J. H., Stafford, G., and K a t e r s , K. A., J . Chern. SOC., 1951, 638. (6) Stamm, H., Alzgew. Chem., 47, 791 (1934). R E c E I r E D for review October 1, 1931. Accepted January 16, 1952. supported in part by a grant f r o m t h e U. S.Public Health Servxe.
'Kork
Densities and Refractive Indices for Diethylene Glycol-Water Solutions GORDON M A C B E T H I AND A. RALPH THOMPSON University of Pennsylvania, Philudelphia, Pa.
S A means of determining the compositions of aqueous
A diethylene glycol ( p , 8' - dihydrosyethyl ether) solutions,
measurements were made on a number of solutions of known composition for density a t 35" C. and for refractive index a t 25" C. Although values of these properties for the purified glycol have been reported in the literature ($), for aqueous solutions only graphical representations of the specific gravity using commercial grade materials could be found ( 1 i. I
I. I O
,
I
The water content of this purified diethylene glycol, as dereimined by Karl Fischer reagent, ivas found to be 0.025% by weight, The value of the refractive index, nVl 1.4461, agrees exactly with the value reported by Rinkenbach ( 4 ) , and the specific gravity At,
,I:;
_.
1.1183, is in close agreeinelit ii-ith previously reportell
values ( 1 ) . This purified diethylene glycol, together with freshly boiled distilled water, n-as used t o prepare nine solutions of various glycol concentrations from 10 to 90 xyeight %. The materia!s were pipetted into 50-ml. ground-glass-stoppered Erlenmeypr flasks, the actual amounts being determined by weighing to 0.1 mg. on an analytical balance. All solution compositions, based on amounts of material weighed and accuracy of the weighing., are known t o within approximately 1 part in 30,000. DENSITY MEA SUR EM ENTS
The density measurements were made using capped, 10-1n1. \Veld-type specific gravity bottles. These were equilibrated in a constant temperature bath maintained a t 35.00' i= 0.02" C. as determined by a calibrated thermometer. Duplicate deterniinations were made on each solution. All the weighings were reduced to values in vacuo and the absolute densities a t 35' C. were calculated as grams per millilit,er. 0
20
40 60 80 WEIGHT % DIETHYLENE GLYCOL
100
Figure 1. Absolute Densities of Aqueous Diethylene Glycol Solutions at 35'C. I n an earlier paper (Z),the authors presented data on densities and refractive indices for the system propylene glycol-water. Purification of materials and methods of measurement were described, and limitations of the data discussed. For the system under consideration, sufficient differences were encountered to make description of these advisable.
The experimental results are listed in Table I . Snioothrd values obtained from a large scale plot similar to Figure 1 are presented in Table 11. An esamination of these data shows that u p t o approximately SOY0 diethylene glycol, the composition should be measurable to xithin approximately 0.03 weight %, Beyond this, the slope of the curve decreases rapidly, as does the usefulness of density as a measure of composition.
1.45
PREPARATION O F SOLUTIONS
For use in preparing the solutions of known compositions, commercial grade diethylene glycol was purified by two successive distillations in a Todd column, 1 inch in diameter by 36 inches high, packed with 3 / , 6 inch glass helices. The absolute pressure was maintained a t 10 to 15 mm. of mercury, and a reflux ratio of approximately 20 to 1 was used in both distillations. The distillate came in contact only with glass, and drying tubes containing anhydrous calcium sulfate were used to prevent contamination with moisture during venting of the receiver. I n the first distillation, the middle 50% of the charge was collected, all within a 1" C. boiling point range. This material was then refractionated, the middle 50% being collected for use in making up the solutions. 1
Present address, The Dow Chemical Co, hlidland, hIich.
n x- 1.41 W
n
z W
> 1.37
a
a '
u. W a
1.33
b/
0
'
I
20 40 60 80 WEIGHT 5. DIETHYLENE GLYCOL
Figure 2. Refracti\e Indices of Aqueous Diethylene Glycol Solutions at 25' C.
100
1067
V O L U M E 24, NO. 6, J U N E 1 9 5 2
composition is hrlon approximately 80% glycol, and the refractive i n t i ~ x(;:++ashould be useful in drterniiriing the glycol cont c s n t to u i t h i i i I0.1 \\-eight yoover the entire composition range. P X P 'water IJr, 1
DG 2 DG 3 DG 4 DG 5 DG 6 DG 7 DG 8
DG Y
9 97 19.79
'I'ali!e
29 70
39 46
1 06303 1 07.m
49 73
69 78 69, 67 79 74 89 8 9
I0
(1
00000
mnni
Purified dic thl-ltne gl)-col
__ REFRACTIVE I S D E X hIEASUREMEh~TS
Refractive index values were measured by means of a Carl h i s s dipping refractometer and a constant temperature bath kept at 25" i 0.1" C. 9 sodium lanip served as the light source. Using this instrument, the values of refractive index are believed to be correct t o within j=O.OOOl. -1s a result of the relatively constant, rate of change of refractive index with composition as shown in Figure 2, the precision mentioned corresponds t o a composition difference of about 5 0.1 weight R over the entire composition range. In summary, the densit'y data presented may be used in detertnining the glycol content within 10.03 weight % when the
I )it,tliylne Gl,.col. Weight
0
10 20 30 40 50 60 70 80 90 100
00 00 00 00 00 00 00 00 00 00
I I.
Smoothed \'slues
Refractive Index,
ns5
Absolute Density, G./RZl. a t 35.00' C.
1.3325 1.3436 1.3550 1 3670 1 3788 1.3912 1.4032 1.4150 1,4261 1,4364 1,4461
0.99406 (3) 1.00733 1.02116 1.03x 1.04964 1.06340 1.07695 1.08695 1.09569 1.10189 1.10555
LITERATURE CITED
(1) Carbide and Carbon Chemicals Corp., New York, "Glycols," 1947.
( 2 ) RIacBeth, G., and Thompson, A. R., ANAL. CHEM., 23, 618
(1951). (3) Reilly, J., and Rae, W. N., "Physico-Chemical Methods," 3rd ed., Vol. I, X e w York, D. Van Nostrand Co., 1939. (4) Rinkenbach, W ,H., Ind. Eng. Chem., 19, 4 i 4 (1927). RECEIYED for review December 8, 1951.
Accepted February 10, 1962.
Determination of Phosphate by lor: Exchange ALEXANDER J . GOUDIE' AND WM. RIERIAN I11 School of Chemistry, Rutgers Cniversity, New Brunswick, .V. .I. RE-EX4SIIN.4TIOX of the ion-exchange procedure for the A ! determination of phosphate ( 3 ) seemed desirable for three
reasons. 1. Since this method was first proposed ( S ) , monofunctional high-capacity resins of the strong-acid type ( 1 ) have become arailable comriiercially in a wide variety of particle sizes. The uje of theye resins permits a more efficient separation of phosphoric acid from interfering cations. 2 . Dijksnian believed that the presence of carbonate in t'he titration was a serious source of error in this determination, and recommended ( 2 ) elaborate precautions for its exclusion. 3. Shortly after the ion-exchange method x-as recommended (3),it \vas observed in this laboratory that positive errors were incurred when the ion-exchange column was subjected to repeated use. Thib error was much worse with a sulfonated polystyrene resin than with Amberlite IR-100. Investigation revealed that the cause of the error vias failure of the regenerat'ion procedure t80remove the ferric ion completely from the column. >lore and more ferric ion was retained by the resin with repeated use unt,il a sufficient quantity was accumulated so t h a t a n apprecisble amount of ferric ion appeared in the eluate with the phosphoTic acid. Then part of the phosphate 1%-asconverted t o the tertiary state a t the second end point ( p H = 8.98). This error amounted to O.i% phosphorus pentoxide after ten determinations had been performed with one column according t o the directions given below, except that only 100 ml. of 4 111 hydrochloric acid \!-ere used in each regeneration. +4sthe removal of iron by hydrochloric acid proved t o be impracticable, diaminonium citrate x a s used as a coniplesing agent in the regeneration. PREPARATION OF COLUMN
Stir 35 grziiia of Dovex-50 (100 to 200 mesh, purchased from bIicrocheniica1 Specialties Co., 1834 University Bve., Berkeley 3, Calif.) with 200 ml. of water in a 250-ml. beaker. Let the coarse particles settle for 1 minute and decant the suspended fine particles into the sink. Repeat this procedure several times until a clear supernatant liquid is obtained. Place a bed of 15 ml. of the resin in a 30-ml. filter tube provided TTith a porous sintered-glass 1 Presenr address, Central Research Laboratory, Allied Chemical and Dye Corp., blorristown, X. J.
disk (Bllihn filter tube KO.8571, porosity 8,from Ace Glass Co. is very convenient). Attach a short piece of rubber tube with a pinch clamp to the bottom of the filter tube. Regenerate the column before each use as follows. Pass through the column 125 ml. of 1 144 diammonium citrate, then 250 ml. of 6 31 hydrochloric acid. Add a little water t o the column, stir the resin, and finally wash it with 250 ml. of water. Open the pinch clamp wide for the flow, but take care that the resin is always covered with liquid. STANDARDIZATION OF 0.1 N SODIUM HYDROXIDE
Prepare 0.1 A- sodium hydroxide by diluting the 18 N solution with carbonate-free water. To standardize the solution, weigh about 350 nig. of pure potassium dihydrogen phosphate, previously dried a t 110" for l hour. Dissolve this in 150 ml. of water and add 2 ml. of 6 144 hydrochloric acid and 3 drops of 0.003 -11methyl orange. ildd 18 11.17 sodium hydroside dropwise until the indicator turns yellow; then add 1 M hydrochloric acid dropwise until the indicator turns red. Titrate n-ith the sodium hydroxide solution, using a p H meter. In the vicinity of p H 4.6 and 9.1 (corresponding t o the formation of primary and secondary phosphates, respectively), add the solution in uniform increments of 0.20 ml. Take as the end points those buret readings for which A2pH is zero. DETER3llS.4TlOX O F PHOSPHORUS Iii PHOSPHATE ROCK
Treat a sample of 0.4 to 0.45 gram in a covered 150-iii1. beaker rrith 15 nil. of 12 -11hj-drochloric acid and boil gently for 30 minutes. Then evaporate the solution to dryness on a hot plate, and bake in an oven a t 110" for 1 hour. Add 2 ml. of 6 M hydrochloric acid and 20 nil. of n-ater in this order. When t,he sample is redissolved, filter the solution, and wash n-ith rrater until the total filtrate is 65 nil. It is convenient to regenerate the colunin during the foregoing steps. Transfer the solution to a dropping funnel attached to the ionexchange column. Pass the solution through the column with the pinch clamp TT-ide open. T h e rate will be about 5 nil. per minute. Wash the beaker, dropping funnel, and column with water until a total of 150 ml. of eluate is collected. Treat this with 18 A4 sodium hydroxide and 1 144 hydrochloric acid, and titrate as in the st,andardixation.
