INDUSTRIAL AND ENGINEERING CHEMISTRY
284
These data are plotted in Figures 4 and 5. From Figure 5 it can be seen that the linear relationship predicted by Equation 3 holds over a fairly wide range of concentrations, the value of k being 0.00599. In repeating the above with two new sets of solutions, the values of k obtained were 0.00603 and 0.00597, respectively. A reliable average of these values is k = 0.0060. A solution, whose concentration was unknown to the observer, was placed in tube II and gave a reading of 44.7 pa. From the curves of Figure 4,this means a concentration of 8.2 p. p. m. Or, the following calculation gives c =
log 50/44.7 0.0060
= -0.0486 0*0060 =
tinguished only with difficulty from 7 or 9 p. p. m., and with certainty from 6 or 10 p. p. m.
Acknowledgments The authors are indebted to Frederick L. Brown of the Rouss Physical Laboratory for many helpful suggestions and to Robert H. Kean of this laboratory for assistance in studying some of the early models of the colorimeter. Our thanks are due the American Instrument Company, Washington, D. C., for building the apparatus and for assistance in solving some of the problems of design.
Literature Cited
8.1 P. P. m.
The correct concentration was 8.0 p. p. m. In comparison with visual methods, by means of Xessler tubes in a roulette comparator (g), a solution containing 8 p. p. m. can be dis-
VOL. 7, NO. 4
(1) Weston
Electrical Instrument Corp., Newark, N. J., Technical
Data, B-1001-A. (2) Yoe and Crumpler, IND. ENG.CHEM.,Anal. Ed., 7 , 7 8 (1935).
R~~~~~~~ April 16, 1935.
A Pressure Regulator for Vacuum Distillation 0. J. SCHIERHOLTZ, Ontario Research Foundation, Toronto, Ontario, Canada
A
NUMBER of devices have been described in recent years for the control of pressure, the most recent being those of Palkin and Nelson (2) and Jacobs (1). The apparatus described below is very simple in construction and is rugged and foolproof. There are no ground joints subject to wear and leakage, no liquids likely to cause corrosion, no electrical contacts subject to disturbance, and no fragile glass parts which cannot be replaced in a very few minutes. The action of the regulator is not affected by traces of impurities in the mercury in the U-tube. The regulator is actuated directly by the vacuum itself without the aid of a secondary outside agency. The only wearing part requiring replacement is the rubber valve seat and this can be cut, without special tools, from any reasonably good rubber sheet. This device is not intended to furnish extreme accuracy, b u t it will control pressures within the accuracy of laboratory thermometer readings over a wide range, with a minimum of attention in the way of adjustment and repairs. While this regulator operates on the flutter-valve principle, the valve never shuts off entirely while in operation (except when the vacuum is first being built up), but the rubber valve seat “floats” an infinitesimal distance from the surface ’of the glass orifice. This makes for smooth operation.
In Figure I (a side elevation of the apparatus) A is a small square of sheet rubber cemented t o a metal plate which in turn is riveted to lever C. B is a glass capillary tube about 4 cm. long and ground down to the edge of the orifice at its upper end. The lower end fits into pressure tubing held by clamp E, the position of which is adjustable by knurled nut G, and which is connected to the vacuum line preferably as near as possible t o the distilling flask. When A closes down on B, the influx of air stops and the vacuum builds up, and vice versa. Lever C revolves on pivot F and has attached to it a threaded stud carrying a counterweight, D, which serves as a fine adjustment for the valve assembly. The metal plate carrying A rojects beyond the rubber square and engages a slot in metal bractet H . K is the main bracket which is bolted t o an instrument board at L. In Figure I1 (an elevation taken at right angles to that of Figure I) M is a wooden beam which swings on knife edge N , hun on bracket P, which is also bolted to the instrument board. To t%e wooden beam is attached U-tube &, the horizontal ortion and right leg of which consists of Pyrex capillary tubing oF3-mm. bore and is sealed at the end, like a closed-end manometer. The left leg consists of Pyrex tubing of 5-mm. bore and is attached to the vacuum line by means of a piece of pure gum tubing filled with short glass cylinders to prevent its coIlapse under vacuum, and at the same time allowing the greatest possible degree of flexibility. Sensitivity can be increased somewhat by increasing the difference between the bores of the two legs of the U-tube. The U-tube is filled with mercury for the full length of the 3-mm. capillary.
JULY 15, 1935
ANALYTICAL EDITION
This apparatus will control the pressure within I mm. and its over-all range i s l i m i t e d only by the depth of the U-tube, up to 760 mm. In order to set the regulator for the r e q u i r e d pressure, the p o s i t i o n of the U-tube with respect to knife-edge N is first adjusted by sliding beam M through the sleeve by means of which it is attached to the knifeedge N until a p p r o x i mately the required pressure is obtained in the system as measured by an independent manometer. When the required presFIG~JRE 111. PHOTOGRAPH OF s u r e i s o n t h e system, APPARATUS beam should be in an aPProximatelY horizontal position. Further adjustment is obtained by means of G and the final regulation may be controlled by means of D.
285
The operation of the assembly is as follows: As the air is exhausted from the system, the mercury in the Utube is drawn up in the left leg only a fraction of the distance which it drops in the right leg; hence a maximum weight of mercury crosses the center of gravity and causes beam M to swing on the knife-edge in such a way as to raise the rubber valve seat, thus allowing air to bleed in through B. As the vacuum decreases the beam swings back tending to close B. Actual1 , in operation, the rubber face on the plate attached to lever C L a t s an infinitesimal distance away from B, never actually shutting it off. This results in very smooth operation, as evidenced by the fact that the oscillation in mercury meniscus of the manometer approaches the limits of ordinary vision. The size of the bore in capillary B should be chosen rather larger for low vacuums than for higher vacuums. A little experience will suggest the size of aperture to use in order to obtain maximum sensitivity.
Literature Cited (1) Jacobs, G.W.,IND.ENG. CHBM.,Anal. Ed., 7,70 (1936). (2) Palkin, S.,and Nelson, 0. A., Ibid., 6, 386 (1934). RECEIVED March 4, 1935.
Determination of Lead Removal of Bismuth Interference in the Dithizone Method C. E. WILLOUGHBY, E. S. WILKINS, JR., AND E. 0. KRAEMER Tumor Clinic of Jefferson Hospital, Philadelphia, Pa.
I
N ANALYZING biological materials such as blood, excreta, tissues, etc., for their lead content by a previously described dithieone method ( I ) , bismuth, if present, seriously interferes, inasmuch as it reacts with the dithieone reagent under the same conditions as specified for lead. Bismuth may often be present in specimens of this kind as a result of previous medication. In order t o extend the applicability of the dithizone method for lead to materials also containing bismuth, the procedure described below was developed and incorpoirated in the original method. Bismuth is separated from the lead before its final estimation by extracting a nitric acid solution of the two metals, which has been adjusted t o pH 2,0, with a chloroform solution of dithieone. Whereas lead does not react and remains in the aqueous phase, bismuth reacts with the dithieone reagent and forms a chloroformsoluble organic complex. B y means of this additional step, amounts of lead ranging from 0.002 t o 0.200 mg. have been satisfactorily recovered from samples of lead and bismuth nitrates containing 0.500 mg. of bismuth. Larger quantities of both lead and bismuth could, in all probability, be handled with equally good lead recoveries.
Procedure GLA.SSWARE AND REAQENTS.These are the same as previously specified ( I ) , with two exceptions. The concentration of dithizone solutioh 1may be increased to facilitate the separation of appreciable quantities of bismuth. The solution should not be so concentrated, however, as to mask the color changes during extractions. With 0.50 mg. of bismuth, for example, a solution containing 0.20 gram of dithizone per liter is suitable. Secondly, another indicator, acid mcresol purple, standardized 0.04 per cent solution, is required. PR~PARATION OF SAMPLE AND SIMULTANEOUS EXTRACTION OF LEADAND BISMUTH.The destruction of organic matter, the removal of lead and bismuth simultaneously from the digest with dithizone solution 1, and the conversion of the lead and bismuth from dithizone complexes to the corresponding nitrates is carried out exactly as described in the original method ( I ) . SEPARATION OF BISMUTH.Two drops of acid mcresol purple are added to the nitric acid solution, which is then adjusted to pH 2.0 by the addition of 5 per cent ammonium hydroxide. At this
point the solution should have a volume of 25 to 35 ml. The solution is extracted with 25 ml. of dithizone solution 1. Inasmuch as the reaction between an appreciable amount of bismuth and dithizone is rapid, the separatory funnel need not be shaken vigorously for more than 2 minutes. After complete settling, the chloroform phase is removed and discarded, 0.2 to 0.4 ml. of the chloroform solution being left in the separatory funnel, to guard against any loss of the aqueous phase. The aqueous solution is reextracted twice more with 5-ml. portions of the dithizone solution. In each of these extractions the separatory funnel is shaken vigorously for 5 minutes to insure the removal of the last traces of bismuth. With 0.5 mg. of bismuth, the first portion (25 ml.) of dithizone solution is changed to a deep wine-red color by the reaction, the second portion (5 ml.) shows little, if any, color change, and the third portion (5 ml.) remains entirely unchanged in color; this indicates that the removal of bismuth is complete. Whether or not a color chan e has occurred is more easily observable during the shaking of t f e separatory funnel than after the subsidence of the chloroform phase. Larger amounts of bismuth would be removed in like manner by extracting with successive increments of the dithizone reagent until a newly added portion undergoes no change in color. Following the bismuth removal, the aqueous phase is
TABLEI. DETERMINATION OF LEADIN SOLUTIONS CONTAININQ 0.5 Ma. OF BISMUTH AS THE NITRATE (In these experiments the lead, as lead nitrate, was added by another chemist in amounta unknown t o the analyats.) Total Lead Lead Found Added Lead Lead Added Found in Blank Recovered Error MQ. MQ. MQ. Mg. Mg. 0,002 0.005 0.008 0.023 0.060 0,100 0.110 0.150 0.160 0.170
0.180 0.190 0.190 0.200 0.200
0.004 0.008
0.010 0.024 0.062 0.103 0.113 0.152 0.162 0.171 0.181 0.193 0.192 0.201 0.203
0.002 0.004 0.002 0.002 0.002 0,002 0.004 0,002 0.003 0.002 0.002 0.003 0.003 0.002 0.003
0.002 0.004 0.008
0.000 -0.001
0.022 0.060 0.101 0,109 0.150 0.169 0.169 0.179 0.190 0.189 0.199 0.200
-0.001 0.000 +0.001 -0.001 0.000 -0.001 -0.001 -0.001 0.000
0.000
-0.001 -0.001 0.000
