Apparatus for Control of Pressure in Distillation G. W. JACOBS,[ Rutgers University, New Brunswick, N. J.
T
current permits a gravitational closing of the capillary. A stopcock, S, or needle valve below the capillary leak permits the rate of leak to be adjusted up to the limit of flow through the particular capillary used. Additional flow is accomplished by the bypassing of the gas through suitable control either by stopcock or needle valve. The solenoid proper was made to specifications for the author by the Struthers Dunn Company of Philadelphia, and given a serial number of CX1388. This solenoid is properly sized to fit down over a 12-mm. outside diameter Pyrex glass tube. The armature was conveniently made by slotting longitudinally and circumferentially a 4- to 5-mm. iron rod 3 cm. in length to reduce eddy currents. This armature is enclosed in a thinwalled glass capsule whose outside diameter clears readily the inside diameter of the 12-mm. outside diameter glass tube previously mentioned. A No. 0 rubber stopper, half bored, which is continually raised and lowered as the pad sealing the capsule must be boiled in alkali (4). This pad seats itself by gravity upon a capillary orifice drawn out and ground plane. The capillary is retained by two rubber glands (simply slices of onehole rubber stoppers correctly dimensioned). Other valves and seats that were tried were: ground glass to ground glass, and rubber plugs more nearly the size of the capillary leak. The former, although reasonably tight, required too much lifting force, while the latter, having a high center of gravity, failed to give reliable seating. H a n d L are Pyrex flasks serving respectively as high- and lowpressure buffer chambers, with outlets M to suitable manometers; B is a 25-watt lamp acting as a ballasting resistor; R is from the receiver of the still or other apparatus whose pressure is to be regulated. The valve proper is thus shown in its relation to its appurtenances, which may be existing equipment.
HE desire of chemists for better methods of controlling pressure has led to many improvements in this type of
apparatus. Huntress and Hershberg (2) give a very comprehensive bibliography on controlling low pressure during distillation. ?;one of the commonly used devices are without certain faults. The widely used method of using a n electromagnetically operated flutter valve (1, 4) against a capillary leak, being independent of any specific mode of
From HiPressure
To' * traps & Vacuum Pump
FIGURE1. SCHEMATICDRAWINGSHOWING VALVEIN CONJUNCTION WITH APPURTENANCES maintaining vacuum, seemed a logical starting point for this work. The recent paper b y Palkin and Nelson (5) describes what appears to be a n extremely fine control mechanism for this purpose. A previous paper by the author (3) describes the use of a n inexpensive valve. The purpose of the present paper is to describe a highly simplified and improved form of valve, whose parts may be easily duplicated. The solenoid valve has certain advantages: It is positive in action, permits smooth regulation of pressure (*0.015 mm.), is universally adaptable to vacuum and pressure, is available for closed systems of inert gases, and works on lighting socket power without relay. This particular valve, moreover, experiences very little wear and is practically free from corrosion, a factor of no little importance in the chemical laboratory. Figure 1 illustrates the principle upon which this valve operates. Control of the capillary leak from a higher to a lower pressure system is managed by automatic activation of the solenoid b y means of the Hershberg and Huntress sulfuric acid manostat (1).
FIGURE 2. DETAILOF IMPROVED SWIVEL The writer considers the Hershberg-Huntress sulfuric acid manostat a great improvement over the ordinary differential manometer employing mercury. In the set-up now in use in this laboratory a simplified swivel for the manostat was installed, replacing their ground-steel joint ( I , Figure 4,
K) This new brass swivel (Figure 2) is simply two concentric tubes, the mutual rotation of which may be arrested by a setscrew through the outer tube bearing into a groove cut encircling the inner tube. The outer brass tube is mounted to a vertical panel by means of the flange, while the Pyrex tube of the manostat, passing through the inner brass tube, is cemented thereto with sealing wax. Connection is then afforded by a short length of pressure tubing, X; furthermore tube H ( I , Figure 4) may be sealed in, necessitating the addition of a stopcock (Figure 1) for draining and refilling, which if always covered with liquid helps
The activated solenoid lifts an encapsulated iron core with rubber pad and permits a flow of gas. Interruption of the coil 1 Present
address, Point Pleasant Beach High School, Point Pleasant, N. J.
70
January 15, 1935
71
ANALYTICAL EDITION
seal and render leaks the more easily detected. This swivel seems to be simpler and more positive than the one described by Palkin and Nelson (5). Control of regulation by this valve was so good as to cause but a slight rimle on the surface of the sulfuric acid in the manostat. The effe^ci upon the mercury level would certainly not be greater than *0.015 mm. When dispensing with relays, no difficulty due to the increased current flowing through the manostat was experienced in many hours of operation. All work was done with alternating current, b u t with direct current, inasmuch as both electrodes are in the same arm, all electrolytic gases will doubtless be reunited a t the interrupting electrode as they Seem to be by the alternating current. (Even if all electrolytic gases were to enter the system a t L, Figure 1, the quantity formed as calculated for 1 mm. pressure b y Faraday’s law and Boyle’s law would be less than 1 cc. per minute, a value negligible compared to the capacity of the pump.) An apparatus of this type has been in use a t the laboratory at Rutgers University since July, 1933. It has proved
capable of performing complete distillations a t predeter-
mined pressures* It is quiet in ‘peration and simple.
ACKNOWLEDGMENT Many thanks are due to the following for technical suggestions: P. A. Hoover, D. L. Cottle, P. V. McIiinney, all of Rutgers University; E. H. Huntress of the Massachusetts Institute of Technology; and J. A. Doremus of Lafayette College.
LITERATURE CITED (1) Hershberg, E. B., and Huntress, E. H., IND.E m . CHEM.,Anal. Ed., 5, 344 (1933). (2) Huntress, E. H., and Hershberg, E. B., Ibid., 5, 144 (1933). (3) Jacobs, G. W., master’sthesis, Rutgers University, 1934. (4) Miller and McKinney, IND. ENQ.CHEM.,20,522 (1928). (5) Palkin, S., and Nelson, 0. A,, Ibid., Anal. Ed., 6, 386 (1934). RECEIVEDMay 7, 1934.
Application of the Glass Electrode to Dairy Products L. R. PARKSAND C. R. BARNES,Pond Chemical Laboratories, Pennsylvania State College, State College, Pa.
T
HE common methods of measuring the pH of milk and its products are the hydrogen electrode, the quin-
hydrone electrode, and t h e colorimetric. The glass electrode and the stick antimony electrode have not been accepted as standard methods for dairy products. The purpose of this investigation was t o determine the pH of whole milk, buttermilk, cream, commercial ice cream mix, and butter; b y glass, quinhydrone, hydrogen, and stick antimony electrodes.
PROCEDURE The electrical potentials were measured by a vacuum-tube potentiometer of design similar to that of Rosebury (8),who used a General Electric FP. 54 vacuum tube and a Leeds & Northrup type 7651 potentiometer. The circuit used for this investigation was modified somewhat to permit the use of a type K Leeds & Northrup potentiometer. A four-pole doublethrow switch was used for &, connected so as to short-circuit the galvanometer terminals of the type K when the potential readings were being made. The glass electrode was of the bulb type, made of 015 Corning glass according to the method of Robertson (7). The bulb,
TABLEI. PH DETERMINATIONS (At 25’ C.)
GLASS
QUINHYDRONE
(GOLD)
HILDEBRAND ANTIMONY
PABTEURIZED WHOLE MILE
6.585 6.587 6.587 6.585 AV.
6.586
6.589 6.586 6.588 6.586
6.585 6.583 6.583
...
6.94 6.95 6.96 6.95
6.587
6.584
6.95
PASTEURIZED BUTTERMILK
Av.
Hg
I
HgCl KC1 (sat.)
4.302 4.304 4.305 4.304
4.304 4.301 4.304
4.84 4.84 4.87
4.306
4.304
4.303
4.85
..
I
Unknown solution O.1NHCI Glass membrane
111
1
%?\sat.)
1
TARLE 11. PH DETERMINATIONS ( A t 260 C.) QUINHYDRONE
(GOLD)
HILDBBRANDBAILEY
ANTIMONY
COMMERCIAL ICB CREAM MIX
6.614 6.614 6.615
6.617 6.617 6.615 6.617
6.615 6.615 6.615 6.617
6.598 6.609 6.613
.,.
7.09 7.05 7.08 7.07
Av. 6.614
6.616
6.615
6.607
7.07
...
PASTEURIZED STNQLB CRBAM
Av.
Hg
The bulb was washed thoroughly mTith distilled water before each determination. The e. m. f. usually increased during the first two or three readings, after which constant values were obtained. The electrode was then checked with a phthalate buffer of pH 5.697 as determined by hydrogen and quinhydrone electrodes. After checking the calibration of the glass electrode with the buffer, another determination was made to make sure that the asymmetry potential of the glass membrane was still constant. The change of asymmetry potential which sometimes occurred during the first two or three readings was probably due to the formation of a thin fatty film over the glass membrane. Quinhydrone electrodes were prepared from platinum foil and plated with gold as recommended by Popoff, ICunz, and Snow (6). To each 50-ml. sample of dairy product 0.2 gram of Eastman’s quinhydrone was added and the mixture was stirred thoroughly before readings were taken. The Hildebrand electrodes consisted of platinum foil 1 em. square, coated with platinum black ap recommended by the Leeds & Northrup Company (3). These electrodes were used with electrolytic hydrogen purified by passing through solutions of mercuric chloride, alkaline permanganate, alkaline pyrogallol, dilute sulfuric acid, and water. The rate of flow was controlled as suggested by Duncombe (8). The Bailey electrode was used as directed by Bailey (1). Antimony electrodes were cast from Mallinckrodt’s c. P. anti-
GLASS
4,305 4.305 4.307 4.307
...
after being blown, was filled with 0.1 N hydrochloric acid and was aged in distilled water for about a month. The cell used was
BUTTER BERUM
6.603 6.601 6.603 6.603
6.600 6.598 6.600 6.600
6.605 6.605 6.603 6.605
6.90 6.88 6.98 6.88
5.995 5.993 5.993
6.003 6.003 6.005
6.001 5.990 5.994
5.994 5.993 5.994
6.64 6.64 6.64
6.603
6.600
6.605
6.91
Av. 5.994
6.004
5.995
5.994
6.64
