1065
V O L U M E 22, NO. 8, A U G U S T 1 9 5 0 try, hes the great advantage that it can process much larger quantities of material than the Craig apparatus. Although the principle involved is identical with that used in Craig's machine, data on the distribution of benzoic acid were ohtained and results compared with the calculated values (Figure 3). Crajg'e system of equal volumes of metbanol and water as heavy phase and equal volumes of Skellysolve C and benaene as the light phase was used (8). The distribution constant for the system used by the authors was found to be 0.55 instead of his v&e, presumably because of difference in composition of the hydrocarbon mixture. The agreement between calcdsted and determined values is mtisfactory, showing that errors due to slight difference in volumes of the U-tubes and to inaccurate cutting a t position 3 are not serious. The results show strik-
ingly, however, the effect of presence of a small amount of low molecular weight acid in tubes 0 to 2 and of failure to permit emulsions to settle completely before proceeding to the next stage (tubes 12 t o 18). llTERATURE CITED
(1) Craig. L. C.. J . Bid. Chem.. 155, 519 (1944). (2) &did.. p. 526. (3) Craig, L. C., Hopeboom. G. H., Carpenter. F. H., and du Vigne8.ud. Vincent. I W . , 168, 665 (1947). (4) Craig, L: C., Snd'Post, Otto, ANAL.CHBM..21. 5M) (1949). ( 5 ) Janteen. "Des fraktionierte DistiUieren und das fraktionierte Verteilen." Berlin. Vedaz Chemie. 1932. ,) Tiedoke, K., thesis, €lamburg. 1928.'
.
-
R e o ~ r v e oJuly 13. 1848.
Molecular Still MICHAEL PRIZNAR, W. A. WILT, AND F. C. NACHOD Sterling- Winthrop Research Institute, Rensscloer, N. Y .
OME improvements in the vertical-type molecular still have been made during the past few years (14). The present note describes a oyclic 5til1, essentially following the design of Quickenhush and Steenhock (6), using a magnetically driven metallic rotor. ,. ' Because some difficulties had been encountered with the glass rotor suggested by Quackenbush and Steenhock (6), it seemed advisable to elaborate on their ha& design. A photograph of the molecuhr still, ready for operition but without the protective Luciteshield, isshown in Figure 1.
A
The liquid to he distilled can be introduced into the still through stopcock St and allowed to drain into storage chamber H. The maguet,ic pump, P, lifts the liquid upward into chamber F,which COWDEWSER G
STNNLESS STEEL OUTLET TVBE
e
STAINLESS STEEL BTlRRER
CROSS SECTION OF ROTOR
Figure 2
Figure 1. Front View of Molecular Still
provides for partial degassing. This ump is made from a hollowed iron core containingone glass baicheck valve with mother check valve ahout 3 inches above in the aystem. $he iron core pieton is supported on a Sichrome wim coil, spring, and is normally outaide the field of the surrounding coll. The coil is a 110~ 0 1 1 alrernatine current. No. 40C11360 (PhilliDs Control Cormration) unit,-which sucks the piston downward upon being brtuared. .\l&ing and breaking ;.I eontact to this Coil is pr0vidcd by a micmsaitch, which in turn ie actuated by theex-ceutcr wheel of B mamldawn motor. This motnr is furthermore contr&dby LVaritran autotransformer, and thus pumpin speeds to correspond to a 1-second cycle (ahout 1 ml. per second$ can be reali~ed. A second chamber, E, immediately above F avoids apatteiug of the liquid material in the system. From F,the distilland flows through stopcock St, whirh 8erves to regulate the flow rate, into
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).
Mair, B. J., Schioktana, S. T., and Rose, F. W . , Jr., J. Reasarch Natl. Bur. Standards, 15, 557 (1935). ( 6 ) Quackenbush,F. W., and Steenbock, H., IND.END.CAEM.,ANAL. ED.,15,468 (1943). (5)
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. Results of Analyses
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
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 21.07 a0.03 -0.04 0.00 10.84 10.62 -0.03 s0.02 0.00 13.63 13.47 * O . 04 -0.01 42.90 42.26 0.67 -0.07 -0.01 -0.04 0.00 11.23 11.17 -0.04 +o.oa 0.00 14.81 14.46 60.07 tO.06
%
A
