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determinations, were made with thermometers calibrated by the U. S. Bureau of Standards and readable to * 0.02'. In the course of the investigation forty-eight individual viscosity values were obtained with seven different samples of the abietic acid, forty-eight viscosity values with six separate rosin I samples, and thirty-one viscosity values with four rosin FF samples. In general, a series of values obtained with any one sample was found to lie very consistently on a smooth curve and to be highly reproducible, but apparently the various series with different samples of the two rosins and abietic acid could differ appreciably. This behavior is, perhaps, not surprising in view of the fact that the materials were commercial products and that viscosity is a property of matter which is often extremely sensitive to small differences in the composition and even in the preparation (thermal history) of the samples. Figure 1, in which the common logarithm of the viscosity (in poises) has been plotted against the Centigrade temperature, shows all the viscosity results in the case of abietic acid. The smooth curve A appears to be fairly representative of these data, indicated by the circles and dots, which have been obtained in the present study. The crosses, lying somewhat below this curve, are the values for abietic acid recently published by Bingham and Stephens (1) as representative of the results found with their alternating stress method. In all cases the authors' results indicated true viscosity and not plasticity; and this was also the conclusion of Bingham and Stephens, who measured a viscosity as large as 7.2 X 10" poises at 20" C. Curves B and C serve to show how results for rosin I and rosin FF compare with those for the abietic acid. To avoid confusion in the figure the individual points for these data have been omitted. It is interesting that the darker, or cruder, rosin has an appreciably higher viscosity than the commercial abietic acid, while rosin I is consistently lower
CHEMISTRY
Vol. 7, No. 2
within the temperature range of this study. At the upper temperatures the authors' rosin curves overlap to some extent the viscosity determinations published by Peterson and Pragoff (8) and in this region the two investigations are in fair agreement. Thus for rosin I, Peterson and Pragoff found a viscosity value of 2.83 poises a t 125' C., while curve B in the authors' study corresponds to 2.5 poises. In the case of rosin FF the earlier investigators found viscosities of 5.95 poises a t 120" C. and 2.56 poises a t 130" C.; and the present study yields 7.4 and 3.3 poises, respectively, a t these two temperatures. TABLE I. VISCOSITYDATAFOR WOOD ROSINAND ABIETICACID TEMP.
ROSINFF Log100
ROSINI Log100
ABIETICACID Logloll
28 30 40 50 60 70 80 90 100 110 I20 130
10:?3 9.00 7.38 5.96 4.69 3.62 2.70 1.93 1.34 0.87 0.52
10.06 9.73 8.11 6.60 5.23 4.04 3.06 2.23 1.54 0.98 0.57 0.27
10.68 10.35 8.71 7.07 5.68 4.40 3.33 2.43 1.78 1.10 0.65 0.31
c.
In Table I are given a series of "best values" for viscosity results with these three materials, obtained by reading off the logtoq values corresponding to even temperatures in an enlargement of Figure 1. For convenience in tabulation the data have been kept in the form of the common logarithm of the viscosity (in poises). LITERATURE CITED (1) Bingham and Stephens, Phusics, 5,217 (1934). (2) Parks, Barton, Spaght, and Richardson, Ibid., 5, 193 (1934). (3) Peterson and Pragoff, IKD. ENQ.CHEM.,24, 173 (1932). RECEIVED January 14, 1935
A Rapid Method of Preparing Biological M.aterials for Phosphorus Determinations H. W. GERRITZ, Agricultural Experiment Station, S t a t e College of Washington, Pullman, Wash. IFFICULTY has been encountered in preparing cattle cubic centimeters of cattle urine are thus digested in 15 minutes and sheep urine for total phosphorus determinations. and 2 grams of feed require about the same time. PhosThe low phosphorus content requires the digestion of phorus determinations on perchloric acid-digested samples large quantities of urine and the removal of the organic matter have been found to be accurate and to compare well with requires vigorous oxidation. In digesting with nitric and determinations by official methods (1). hydrochloric acid, it is practically impossible to obtain a clear Very good recovery of added phosphorus has been made. solution. Sulfuric-nitric acid digestion with further addition Table I shows the accuracy with which phosphorus may be recovered from s t a n d a r d of nitric acid or sodium nis o l u t i o n s gravimetrically, trate requires 2 hours' divolumetrically, 01colorimetgestion or more to clarify TABLE1. RECOVERY OF pHosPHoRUs AFTER PERCHLORIC ACID urine samples. The same DIGESTION OF STANDARD SOLUTIOXS rically, after perchloric acid (Phoaphorus added a6 K2HPOd digestion. Standard solumethod of digesting feeds VOLUM~TRIC COLORIMETRIC t i o n s of potassium phosand feces requires 1 to 2 GRAVIMETRIO METHOD METHOD METHOD phate were placed in Kjelhours. Recovered Recovered Recovered dah1 flasks and filter paper The use of perchloric acid after after after in with nitric Phos horue €IC104 Phos horus HClOa Phos horus HClOi afded digestion a&ed digestion acfded digestlon was added to Organic and sulfuric acids or with Gram Gram Gram Gram Gram Gram matter. The organic matter 0.0060 0 0060 0 0017 0.0018 0.0057 0 0057 was removed by oxidation sulfuric acid alone has been 0 0019 0 0057 0 0058 with sulfuric, nitric, and perfound to accelerate the clari0 0058 0.0017 0.0057 0 0058 0.0019 0.0057 chloric acids, as in determif i c a t i o n a pp,r ecia b l y 0.0058 0.0018 0.0057 0.0060 0.0018 0.0057 nations of phosphorus on through r a p i d , v i g o r o u s oxidation. T w e n t y - f i v e biological materials.
D
March 15, 1935
ANALYTICAL EDITION
117
TABLE 11. PHOSPHORUS IN URINESAMPLES BY COLORIMETRIC METHOD -SULFURIC-PERCHLORIC
A5
B"
%
%
--
(25-cc. duplicate samples of urine digested by each method) ACIDDIGESTIONSULFURIC-NITRIO ACIDDIGESTIONDifferDiffer~. ence AV. A B ence
%
%
%
0.0010 0.0009 0.0001 0.0009 0.0009 0.0009 0.0009 0.0000 0.0009 0.0009 0.0011 0.0011 0.0000 0.0011 0.0011 0,0022 0.0001 0.0021 0.0021 0,0022 0.0064 0.0001 0.0063 0.0063 0.0063 0.0125 0.0000 0.0125 0,0125 0.0125 A and B are duplicates of the original sample treated in the same manner.
Table I shows good recovery of phosphorus in all cases. Satisfactory results were also obtained by comparing phosphorus found in biological materials after rapid perchloric acid digestion with that found after more tedious methods.
DIGESTION OF URIXESAMPLES Twenty-five or 50 cc. of urine were pipetted into a 500-cc. Kjeldah1 flask and 5 to 10 cc. of concentrated sulfuric acid were added, The flask was heated until copious white fumes were no longer evolved. One cubic centimeter of 70 per cent perchloric acid was added to the hot solution and the boiling continued. If the solution did not become water-clear in about 5 minutes, another 0.5 cc. of perchloric acid was added. The solution was boiled for a short time after becoming clear, cooled slightly, and 50 cc. of water were added cautiously. This was transferred to a volumetric flask, cooled, and made up to volume. The phosphorus was determined either volumetrically or colorimetrically. A very offensive odor accompanied sulfuric acid digestion of urine up to the time the perchloric acid was added. When ventilation was poor, it was therefore found advantageous to add 10 to 15 cc. of concentrated nitric acid to the urine a t the time sulfuric acid was added. The digestion was then completed with perchloric acid as before. The complete digestion required 15 to 25 minutes. The results obtained by the rapid sulfuric-perchloric acid digestion and by the slower nitric-sulfuric acid digestion of aliquots of the same sample are given in Table 11. Good checks were obtained by 0.0001 per cent, showing that the rapid method with perchloric acid is at least as accurate as the slower method.
DIGESTION OF FEEDS, FECES, AND FERTILIZERS Feeds, feces, and fertilizers have been digested for phosphorus determinations by heating 15 minutes with sulfuric, nitric, and perchloric acid. In many cases the ube of nitric acid is unnecessary. From 1- to 4-gram samples were placed in 500-cc. Kjeldahl flasks. Fifteen cubic centimeters of sulfuric acid were added, then 15 or 20 cc. of nitric acid. The flask was swirled to facilitate mixing, and heated gently under a small flame until danger of frothing had passed. The boiling was then continued with a full flame until copious white fumes were no longer evolved. Qne cubic centimeter of 70 per cent perchloric acid was added and the boiling continued. If the solution did not clear up in 5 minutes, another 0.5 cc. of perchloric acid was added. When the material oxidized with difficulty it was sometimes found expedient to add a second portion o! nitric acid at the time copious white fumes were evolved, and then to heat again to white fumes before adding the perchloric acid. It has rarely been necessary -to add a second portion of nitric acid. The analysis was completed gravimetrically or volumetrically, with equally good results. The author has used this digestion successfully in the analysis of several hundred samples for phosphorus during the past three years. Before applying the method t o different types of material, samples were prepared by perchloric acid digestion in duplicate, and at the same time samples of the same material were digested by accepted procedures (1). The results are tabulated in Tables 11, 111, IV, and V. Data obtained from these comparisons are presented without choice
DIFFERENCE BETWEEN
METHODS
. .. . AV.
%
%
%
%
0.0009 0.0009 0.0012 0.0022 0.0064 0,0125
0.0000 0.0000 0.0001 0.0000 0.0001 0,0000
0.0009 0.0009 0.0011 0.0022 0.0063 0.0125
0.0000 0.0000 0.0000 0.0001 0,0000 0.0000
TABLE111. PHOSPHORCS 1;2' POULTRY FEEDS BY VOLUMETRIC METHOD Av.
DIQESTION WITH NaN03, HNOa, AND DifferA B ence Av.
%
%
DIGESTION WITH HC104, HNOa, AND
HnSOa
A
B
Difference
%
%
%
0.98 0.97 0.91 1.07 1.16 0.55
0.96 0.83 0.92 1.03 1.18 0.54 Av.
0.02 0.14 0;Ol 0.04 0.02 0.01 0.04
0.97 0.90 0.92 1.05 1.17 0.55
0.92 0.97 0.92 1.06 1.12 0.52
%
%
0.92 0.95 0.87 1.11 1.12 0.50 Av.
0.00 0.02 0.05 0.05 0.00 0.02 0.02
DIFFERENCE BETWEEN
METHODS
% 0.92 0.96 0.90 1.09 1.12 0.51 Av.
% -0.05 $0.06 -0.02 4-0.04 -0.05 -0.04 0.04
TABLEIV. PHOSPHORUS IN PASTURE GRASSBY VOLUMETRIC METHOD DIGESTED WITH HClOa, HNOa, AND
A % 0.63 0.61 0.65 0.65 0.43 0.45 0.42 0.66 0.41 0.42 0.41 0.46
&So4
B % 0.65 0.63 0.67 0.66 0.44 0.45 0.44 0.66 0.41 0.41 0.42 0.48 Av.
Differenoe
DIFFERENCB
7 A A B H E D -
%
%
A %
0.02 0.02 0.02 0.01 0.01 0.00 0.02 0.00 0.00 0.01 0.01 0.02 0.01
0.64 0.62 0.66 0.66 0.44 0.45 0.43 0.66 0.41 0.42 0.42 0.47
0;66 0.67 0.63 0.58 0.45 0.45 0.46 0.60 0.44 0.45 0.46 0.47
Av.
B % 0.67 0.64 0.60 0.66 0.45 0.43 0.44 0.60 0.43 0.45 0.46 0.46
Difference
%
0:ol 0.03 0.03 0.08 0.00 0.02 0.02 0.00 0.01 0.00 0.00 0.01 Av. 0.02
BETWEEN
Av. METHODS % G7" .0.67 $0.03 4-0.04 0.66 -0.04 0.62 0.62 -0.04 0.45 $0.01 0.44 -0.01 0.45 +0.02 0.60 -0.06 0.44 $0.03 0.45 $0.03 +0.04 0.46 0.47 0.00 Av. 0.03 I -
TABLEV. PHOSPHORUS IN FERTILIZERS BY GRAVIMETRIC METHOD DIGESTED WITH HClO4, HNOa, DIGEBTED WITH NaNOa, "Os, AND HsSO4 AND &SO4 DifferDifferA B ence Av. A B ence Av.
% 4.29 4.28 2.85 4.63 4.40 2.27 4.85 4.89 4.07 2.93 6.34 4.91 4.56 3.68 3.65 2.79
% 4.26 4.27 2.81 4.65 4.59 2.24 4.97 4.92 4.14 3.98 6.32 4.97 4.58 3.65 3.74 2.84 Av.
%
%
%
%
0.03 0.01 0.04 0.02 0.19 0.03 0.12 0.03 0.07 0.05 0.02 0.06 0.02 0.03 0.09 0.05 0.05
4.28 4.28 2.83 4.64 4.50 2.26 4.91 4.91 4.11 2.96 6.33 4.94 4.57 3.67 3.70 2.82
4.34 4.27 2.79 4.53 4.53 2.23 4.97 4.92 4.14 3.01 6.32 4.90 4.55 3.79 3.50 2.76
4.24 4.32 2.84 4.57 4.78 2.35 4.91 4.86 4.14 2.93 6.34 4.92 4.52 3.70 3.52 2.83
%
0.10 0.05 0.05 0.04 0.25 0.12 0.06 0.06 0.00 0.08 0.02 0.02 0.03 0.09 0.02 0.07 Av. 0.06
% 4.29 4.30 2.82 4.55 4.66 2.29 4.94 4.89 4.14 2.97 6.33 4.91 4.54 3.75 3.51 2.82 Av.
DIAFERENCE BETWEEN
METHODS
% +0.01 $ 0 . 02 -0.01 -0.09 4-0.16 $0.03 +0.03 -0.02 +0.03 $0.01 0.00
-0.03 -0.03 +0.08 -0.19 0.00 0.04
or repetition, so that a complete picture of the comparison may be obtained. For both volumetric and gravimetric determinations official methods (1) were used after digestion was completed. The colorimetric method used was that of Zinzadze (S), modified t o use Zinzadze (9) molybdenum blue reagent. DISCUSSION The use of perchloric acid in digesting appreciable quantities of biological material results in a much more rapid method for phosphorus determinations than any hitherto presented. Results so obtained were accurate both in recovery of added
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phosphorus and in determination of phosphorus in biological materials. The average difference in results by the two methods is, in most cases, less than the difference between duplicates by either method. Only in the case of the gravimetric determination on pasture grass, Table IV, is the difference greater. In the gravimetric analysis of fertilizer as shown in Table V, the difference between the two methods is less than between duplicates in either one. In all cases the difference is small. SUMMARY In making phosphorus determinations on biological materials, the addition of perchloric acid during the sulfuric-nitric acid method of digestion decreases the time required for the digestion from hours to about minutes* A water-c1ear solution is obtained. This n-&hod of digestion results in no loss and the phosphorus may be accurately determined on the
CHEMISTRY
Vol. 7, No. 2
solution volumetrically, gravimetrically, or colorimetrically without interference. ACKNOWLEDGMENT The author is indebted to H. L. Cole, assistant professor in chemistry, for his help during the earlier part of the problem, and to H. K. Murer, who is studying the Zinzadze method, for his help on that portion of this work. LITERATURE CITED (1) ASSOC.Official Agr. Chem., official and Tentative Methods of Analysis, 3rd ed., 1930. (2) Zinradae, R,, Bull, 8oc. chim,, (4)49, 8,2-9 (1931). (3) Zinzadae, C. R., 2. Pflanzenerndhr. DOngung, 16A, 129-84 (1930). RZCEIVED February 1, 1935. Thia work was begun by the Puthor in the Department of Chemistry. Soientifio Paper 302, College of Agriodture and Experiment Station, State College of Washington.
Recovery of Silver and Iodine from Silver Iodide JOSEPHR. SPIES,Insecticide Division, Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, College Park, Md.
T
HE accumulation of a quantity of silver iodide-oxide
residues, in methylation studies involving silver oxide and methyl iodide, necessitated the recovery of the silver and iodine. A survey of the available methods indicated the lack of any by which both free iodine and silver can conveniently be recovered. Chlorine (2), hydrogen chloride ( I ) , and ferric chloride (4) have been used to convert silver iodide to the chloride, but no mention of the use of aqua regia for this purpose could be found. Aqua regia (1 part of concentrated nitric acid to 3 parts of concentrated hydrochloric acid by volume) reacts smoothly and quantitatively with silver iodide to form the chloride. The reaction proceeds vigorously although not violently, without external heating and with the evolution of only a small amount of brown oxide of nitrogen. The silver iodide should be ground to pass a 40-mesh sieve and the mixture shaken frequently to hasten the reaction. In dealing with large quantities, or if the silver iodide is not finely ground, more than one treatment may be required to complete the transformation. After completion of the reaction the aqua regia is diluted with water to precipitate dissolved halides and the residue filtered and washed with water. The chloride is separated from unconverted iodide by shaking with concentrated ammonium hydroxide. If necessary, the treatment with aqua regia is then repeated until no residue remains upon shaking with ammonium hydroxide. Reduction of the silver ammonium chloride, in excess ammonium hydroxide, is accomplished by sodium hyposulfite as suggested by Firth and Higson (5). The iodine monochloride, which is formed by the action of aqua regia in the process, is stable in the acid solution. Hydrolysis of the iodine monochloride, by which eight-tenths of the iodine is precipitated and two-tenths converted to iodic acid, is brought about by adding sodium hydroxide to the diluted aqua regia until it is just acid to litmus (6). In neutralizing the acid an excess of alkali must be avoided to prevent solution of some iodine. After filtration of the iodine, the mother liquor should be tested by adding more acid or alkali. If the correct acidity was not attained, this will cause additional iodine to precipitate. The remaining two-
tenths of the iodine, in solution as iodic acid, is precipitated by the addition of the calculated amount of sodium hyposulfite solution. An excess must be avoided, otherwise iodine will be reduced further, yielding soluble sodium iodide. The calculation of the required amount of hyposulfite was based on Equation 5 given below. These two steps may be carried out in the same operation by adding the hyposulfite solution after the first precipitation of iodine. The acidity of the solution should again be adjusted after adding the hyposulfite. The iodine is recovered by filtration of the cold solution on a Buchner funnel, using a hardened paper. It is washed with ice water and dried in a desiccator over concentrated sulfuric acid. In dealing with silver iodide-oxide residues, the silver oxide is removed by first extracting with dilute nitric acid. The silver iodide remains undecomposed and the dissolved silver is precipitated by reduction of its ammoniacal solution with sodium hyposulfite as in the case of silver ammonium chloride (5). The reactions involved in this recovery process are represented by the following equations: Conversion of silver iodide to chloride: HNOs 3HC1+ Clz NOCl 2Hz0 AgI Clt 4AgCl IC1 Hvdrolvsis of iodine monochloride: b.3 4 H20--f HCI €110 5HI0 +212 HIOs 2H2O Reduction of iodic acid: 6HIOa 6NazSz04 2H20+31z 10NaHS04 (5)
++ ++
++
+
+
+
+
8 8
+
The method was developed for the recovery of silver and iodine from residues, but in order to study the reaction pure silver iodide was employed, since it is the unreactivity of this substance which presents the difficulty in the procedure. A description of a typical experiment is given below and the method has been successfully employed starting with a 600gram lot of silver iodide-oxide residues.
EXPERIMENTAL CONVERSION OF SILVER IODIDE TO CHLORIDE.To 75.0 ams (0.32 mole) of silver iodide (40-mesh) were added 61 ml. oycon-
