ANALYTICAL CHEMISTRY
1066 distillation chamber D,which contains the stainless steel rotor, comprising clutch magnet,. shaft, ball bearings, and stirrer, the oonstruction of which is shown in detail in Figure 2. The rotor consists of a brass housing supported on top of the distillin chamber on ball bearin e., and a stainless steel stirrer attache2 to it. The precision-buift stirrer is aligned perpendicularly to the distilling chamber with a level and is centered by groper clampin of the anchor ring, B , to the disk, A , of the metal ousmg. An flnico ma et, connected to a high-torque direct current motor (G. I(.H e l g Company), is centered and supported very close to the surface of A . The cylindrical stirrer has twelve equal sections cut out for reducing weight and allowing distillation to take place. The precision glass tubing (Glo-Tech recision-bore borosilicate glass tubing, obtained from Fischer & orter Co., Hatboro, Pa., and flanged on a glass-working lathe), which serves a8 the wall of the distillation chamber, D, is heated from the outside by a Glas-Col mantle, the temperature of which is controlled by another Varitran and is measured by a Brown potentiometer. The clearance between the stirrer and the inner wall of the recision-bore tube is 0.005 inch. The con&nser, G, is equipped with both inlet and outlet stainless steel tubing for liquid cooling. The system is evacuated by a Cenco Hypervac backing pump, R, and a two-stage oil diffusion pump, 8,manufactured by Distillation Products, Inc. Vacuum control is maintained by the Pirani gage, Q, and the McLeod gage, M . The amount to be distilled is governed by the dimensions of etorage chamber H and charges from 100 ml. to 1 liter can be recycled conveniently.
f:
The unit has been wed successfully in the distillation of certain natural products which proved refractory to conventional d k tillation techniques. The results of this work will be reported elsewhere. ACKNOWLEDGMENT
The mistance of H. Rayford Fry, Jr., and Frederick J. Schults, of the mechanical department of WinthropStearns, Inc., is gratefully acknowledged. Thanks are also due to G. W. Ewing, Union College, Schenectady, N. Y., for help in the original design of the unit. LITERATURE CITED (1) Hickman, K. C. D., I d . Eng. Chem., 29, 968 (1937). (2) Zbid., 4 2 , 3 6 (1950). (3) Hickman, K. C. D. (Eastman Kodak Co.), U. S. Patent 1,942,858 (Jan. 9,1934). (4) Jewell, W., Mead, T. H., and Phipps, S.W., J. SOC.Chem. Id., 5 8 , 5 6 (1939). (5) Mair, B. J., Schioktana, S. T., and Rose, Natl. Bur. Standards, 15, 557 (1935).
F. W . , Jr., J. Reasarch
( 6 ) Quackenbush, F. W., and Steenbock, H., IND.END.CAEM.,ANAL. ED., 15,468 (1943). RBCEIYEDOctober 28. 1949.
Determination of Arsenic in Insecticides Application of Ion Exchange JUNE T. ODENCRANTZ AND WILLIAM RIEMAN I11 Rutgers University, New Brunswick, N . J. ETHODS are proposed for the determination of total, M trivalent, and quinquevalent arsenic in insecticides. The distinctive feature of these methods is the separation of all interfering cations from the arsenic, by passage through a column of hydrogen-ion exchanger. The arsenic in the eluate is then determined by conventional iodometric procedures. The official procedure of the h o c i a t i o n of Official Agricultural Chemists for the determination of total arsenic in insecticides ( 1 ) involves reduction of arsenic to the trivalent state, separation of arsenious chloride, and iodometric titration of a neutralized and buffered aliquot of the distillate. T h e lengthy distillation of this procedure can be eliminated by using ion exchange to isolate the arsenic. There are other applications of ion exchange to analytical chemistry (2,s). The proposed method for total arsenic involves oxidation of the arsenic to the quinquevalent state, separation of arsenic from interfering cations in 5 minutea by use of an ion-exchange column, and titration of the quinquevalent arsenic with thiosulfate. This procedure requirea less time and space than the distillation procedure, especially when several samples are analyzed simultaneously.
be purchased from the Ace Glass Company, Catalog No. 8571 porosity B. The rate of flow through each tube was regulated by a Hoffman clamp attached to a iece of rubber tubing fitted to the lower end of the filter tube. two-hole stopper with a 125-ml. separatory funnel was fitted into the top of each filter tube. A bed volume of 12 ml. of 60- to 100-mesh Ion-X assured the uantitative removal of all cations by the recommended p r o m lure. This sulfonic acid resin may be purchased from Microchemical Specialties Company, 1834 University Ave., Berkeley 3, Calif. It is necessary to regenerate the resin bed before each run. The columns are first backwaahed for a few minutes by a reverse flow of water. Then 350 ml. of 2 N hydrochloric acid and 200 ml. of water are passed through each column a t the rate of 20 ml. per minute.
1
PROCEDURES
Determination of Total Arsenic. Weigh 200 mg. of sample into a 160-ml. beaker, add 7 ml. of 15 N nitric acid, and bring to a boil on a hot plate. Add 3 ml. of 2 N potassium bromate and evaporate to dryness. Backwash and regenerate the resin during this evaporation. Dissolve the residue in 2 ml. of 6 N hydrochloric acid without heating, and add 8 ml. of water. Filter this into the separatory funnel and wash the filter with three succes-
REAGENTS
Hydrochloric acid 2.0 N , 2.4 N , 6.0 N,and 12.0 N . Nitric acid, 15.0 d. Potassium bromate, 2.0 N . Sodium bicarbonate, reagent grade. Potassium iodide reagent grade. Standard thiosu1h.e solution, 0.05 N , standardized against POtassium dichromate. Sodium hydroxide, 10 N . Phenolphthalein indicator, 1%. Standard iodine solution, 0.05 N,standardized against arsenic trioxide.
Table I.
1
Chief Metallic Comtituenta Lead
2
Calcium
3
Calcium Copper Copper
Sample No.
4
Calcium Copper
6
APPARATUS
The apparatus consisted of several boro!ilicate glass Allihn filter tubes, 10 om. in height and 2.7 om. in diameter, wluch may
6
,
h&mium
Results of Analyses
A.O.A.C. Method Total Aa,
%
20.96 -0.02 10.67 -0.01 13.43 -0.03 42.71 -0.oa 11.14 -0.10 14.47 -'0.07
Proposed Method Total Aa, As (III), As V), %
%
20.82
0.00
10.62 -0.03 13.47 -0.01 42.90 -0.07 11.17 -0.04 14.46 60.07
0.00
-0.04
0.00 42.26 -0.01 0.00 0.00
A
21.07
a0.03 10.84 s0.02 13.63 * O . 04 0.67 -0.04 11.23
+o.oa
14.81
tO.06
1067
V O L U M E 2 2 , N O . 8, A U G U S T 1 9 5 0 sive 10-ml. portions of water. If the residue dissolves com letely in the 2 ml. of 6 N hydrochloric acid, omit the filtrdion angdilute the solution to 40 ml. in the separatory funnel. Let the solution flow through the column of resin a t a rate of 20 ml. per minute, and collect the eluate in a 250-ml. Erlenme er flask. Wash the se aratory funnel and column with one 20-mf portion and one 40mll portion of water. Add 50 ml. of concentrated hydrochloric acid to the eluate to bring the concentration of this acid up to 4 M . Add 1 gram of sodium bicarbonate, 0.2 gram a t a time, swirling all the while. Add 1 gram of potassium iodide, stopper the flask, and swirl until all the iodide is dissolved. After 5 minutes, titrate, without starch indicator, with 0.05 N sodium thiosulfate to the disappearance of the iodine. Recognition of the end point may be facilitated by performing the titration on a porcelain stand. In the presence of starch, the reaction between iodine and thiosulfate is retarded, so that an appreciable quantity of thiosulfate reacts with the acid. The size of the sample should be decreased to about 0.1 gram with insecticides containing over 3070 of arsenic because the end point becomes indistinct if more than 30 ml. of thiosulfate are used in the titration. Procedure for Quinquevalent Arsenic. Weigh 200 mg. of sample into a 150-ml. beaker and add 10 ml. of 2.4 N hydrochloric acid. Place in a water bath between 60" and 80" for 15 minutes. Filter the sample and proceed as previously described. Procedure for Trivalent Arsenic. Weigh 200 mg. of sample into a 150-ml. beaker and add 10 ml. of 2.4 N hydrochloric acid. Place in a water bath between 60" and 80" for 15 minutes. Filter the sample and wash through the column as previously described
Neutralize the acid present in the eluate with 10 N sodium hydroxide and adjust to the acid side of phenolphthalein with dilute hydrochloric acid. Add 4 or 5 grams of sodium bicarbonate. Titrate the solution with 0.05 N iodine using starch as an indicator. RESULTS
The results of the analyses together with the mean deviations, presented in Table I, indicate that the accuracy and precision of the recommended methods are satisfactory. Each entry in the table is the mean of at least three determinations. ACKNOWLEDGMENT
The authors Itre grateful to the Research Council of Rutgers University for financial aid in the investigation and to Kenneth Helrich of the Agricultural Experiment Station of Rutgers University for samples used in the analyses. LITERATURE CITED (1) Aasoc. Offic. Agr. Chemists, "Official and Tentative Methods of
Analysis," 6th ed., p. 53, 1945.
(2) Kunin, Robert, ANAL.CHEM..22, 64 (1950). (3) Nachod, F., "Ion Exchange," S e w York, Academic Press, 1949. RECEIVED October 28, 19-19. Presented before the Division of Analytical and Micro Chemistry at the 116th Meeting of the A\IEWCAXCHEWCAL SOCIETY, Atlantic City, N. .J.
33, 34, 35. Symmetrical Diphenylurea, Unsymmetrical Diphenylurea, and Potassium Chlorate
4
Contributed by WALTER C. MCCRONE, Arrnour Research Foundation of Illinois Institute of Technology, Chicago, Ill.
N RECENT months, inquiries have been received requesting Ierythritol, crystallographic data on the following compounds: penðer dipentaerythritol, pentaerythritol tetraformate, onitrophenol, diphenyl, apocupreine hydrobromide, and vanadium fluorides. Any information on the crystallography of these compounds, no matter how fragmentary, should be sent to the National Registry of Crystallographic Data, in care of the author, who will transmit the information to interested parties. During the course of this program, a number of incomplete descriptions have accumulated. Although in some cases these compounds merit completion, most of them are less common or less important and would not be completed. The data are, however, accurate 90 far as they go and furnish adequate information for analytical purposes. Three of these partial descriptions are, therefore, being published this month. The orientations of the crystallographic axes are based on morphology and might change if x-ray diffraction data were available. Each has, however, been reoriented to agree with the conventions used in this series. 93.
SYMMETRICAL DIPHENYLUREA (CARBANILIDE)
:
C&-
\
7" 4
Car-N
Struetural Formula for Symmetrical Diphenylurea
C
-a
l
a
oii
I
A
Figure 1. Orthographic Projec-
tion of Typical Crystal of Sym-
metrical Diphenylurea
CRYSTAL MORPHOLOGY (see Figure 1) Crystal S stem. Orthorhombic. Form anc?Habit. Tablets from hot ethyl alcohol are flattened parallel to b with rism l l O ) , and macrodome { 1011, showing also ioloy, (oolj, and brachydome [ 011 ). Axial Ratio. a : b : c = 0.8957:1:0,5712; 0.8611:1:1.1165 (a). Interfacial Angles (Polar). 110 A 110 = 96'; 011 A o l i = 105'.
lvl,
