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INDUSTRIAL A N D ENGINEERING CHEMIXTRY
Vol. 16, No. 2
An Automatic Pressure Regulator' By Louis E.Dawson BURSAUOF
CHEMISTRY,
WASHINGTON, D.C.
N MAKING some measurements of rates of filtration it with the closed end sealed to a small bent tube 6 or 8 mm. was desirable to maintain the pressure constantly at 500 in diameter, to which a small separatory funnel, h, of about mm. less than atmospheric pressure over a period of an 100-cc. capacity is connected by means of a rubber tube, i. hour or more, by automatic means. Several attempts By means of this separatory funnel the height of the mercury were made to devise an arrangement which would hold in the main reservoir g may be adjusted. The lower end the pressure constantly at a certain vaIue and would not of the tube d should not be too close to the bottom of the reservoir g. The various members of the regulator are require personal supervision. The apparatus described herein very satisfactorily main- supported by means of clamps on a ring stand. tained a steady pressure for a period of days with a maximum When adjusting the regulator, the vacuum is slowly built variation of only 2. or 3 mm. of mercury when operating up in the system to be evacuated and enough mercury to under 500 mm. vacuum. This variation, which occurred cover the ends of both tubes d and e is allowed to flow over only for a fraction of a second, was due to admission of air by into the main reservoir g from the the regulator. With differences in atmospheric pressure separatory funnel h until the mercury no adjustment of the apparatusbis necessary when the pres- in both tubes d and e has risen into sure is measured with a mercury manometer which has one the trap a and a manometer indicates end open to the atmosphere and the other end connected the desired pressure, Then the sepwith the system. This holds true only when atmospheric aratory funnel is lowered and the pressure is being used-thst is, when the effective pressure mercury level in g is brought down desired is the difference between the atmospheric pressure to the lower end of the small tube e, and a second pressure mechanically produced. The regu- when air is sucked up through this lator, as described here for systems under pressure less tube and the mercury returns to the than that of the atmospheric, may be used for pressures reservoir g through' the large tube CE greater than atmospheric pressure by making a slight modi- and closes the end of the small tube fication. e. When the pressure subsequently The regulator consists essentially of a form of trap or becomes reduced, the end of e is unbaffle connected by means of two vertical tubes of different covered, air is again allowed to pass diameters and lengths with a reservoir of mercury exposed in, and the cycle continues, allowto the atmosphere. Its action depends upon the passage ing the proper mercury level to be set. of a certain quantity of air through the tubes of smaller The regulator should be connected diameter when enough mercury in the reservoir to uncover to a suction flask with a capacity the lower end of the smaller tube has been forced through both of 2 or more liters, as a reservoir to tubes into the trap. The passage of this air alters the pres- furnish capacity so that the small sure, and further passage of air is stopped when the mer- quantity of air admitted through the cury in the reservoir rises, owing to its return through the regulator will not cause too great a larger tube, and closes the end of the smaller tube. change in pressure. When working The trap prevents the mercury from being carried over into with a large vacuum pump of high the evacuated system when a quantity of air is permitted capacity, such as is used for supplyby the regulator to enter the system. It should be so con- ing vacuum to buildings containing structed that the mercury, violently sucked up with the ad- several laboratories, it is necessary mitted air, is rapidly returned to cover the top of the two to have the valve to the system only tubes. It may be made from a test tube, a, about 3 cm. in partly open, or to insert a small diameter and 18 cm. long, with an L-shaped side tube, b, 2.5 capillary tube to furnish friction; cm. in diameter with one arm 4 cm. and the other 7 cm. long, otherwise, with the dimensions used sealed in about 3 cm. from the closed end of the test tube for the tubing and trap, the suction and with the long arm of b turned facing the opposite direc- of air through the regulator will come tion to that faced by the open end of the test tube. To a t too rapid intervals. By choosing the free end of b is sealed a 6 or 8-mm. tube, c, by which tubes d and e with larger dimensions, a the regulator is connected to the system which it is desired regulator suitable for use with pumps to maintain a t constant pressure. of large caDacitv may be made. Into the open end of the test tube part of the trap is fitted If i i is desired to work with pressures other than 500 mm. a rubber stopper having two holes. Through one hole is vacuum, the lengths of the tubes connecting the reservoir passed a glass tube, d, 10 mm. inside diameter and 47.5 cm. with the trap will need to be altered to meet the special long, while through the other hole is passed a smaller glass conditions. They should be such as to aIlow about 3 to 5 tube, e, 3 mm. inside diameter and 46 cm. long, with the cm. of mercury to be in the trap above the top ends of the opposite end, f,flared open to about 10 mm. diameter. With- tubes d and e. This prevents too violent spurting of the out this flared end the regulator is less sensitive and there- mercury into the trap. Moreover, for pressures beyond the fore allows greater fluctuation. range of the capacity of the smaller tube, e, used here, as also The free ends of the two tubes, d and e, dip into mercury with systems having much greater pump capacity, the diamheld in a reservoir, g, 4 cm. in diameter and 11 cm. long, made eter of the tubes should be changed accordingly; that is, when a much lower vacuum on the same pump or when a 1 Received October 23, 1923.
I
February, 1924
INDUSTRIAL A N D ENGINEERING CHEMISTRY
pump of higher capacity is used, more air must be admitted to the system in the same interval of time, so that tubes d and e of greater diameters may be necessary in order to give a regulator of the same degree of sensitivity. When working with systems under pressures greater than atmospheric, the following slight modification of the regulator described should be made: Tube c is left open to the air, while the reservoir g is closed with a rubber stopper hav-
161
ing three holes, two of which hold tubes d and e and the. third a tube 6 or 8 mm. in diameter, which is also connected by rubber tubing to the system under pressure. When this is in operation it allows excess air to escape automatically into the atmosphere from the system. The diameters of tubes d and e should be chosen according to the sensitivity desired and the pressure pump capacity and the pressure desired in the system under control.
Surface Tension of Gelatin Solutionsls2 By Clarke E. Davis, Henry M. Salisbury, and M. T. Harvey NATIONAL BxscurT Co., Nsw YORK,N. Y.
The Morgan method has been used to determine the drop weighfs of gelatin solutions. These determinations are made with apparent ease f n concentrations up to nearly IO per cent when the temperature has been raised aboae the transition point giaen heretofore as 38 O C. Further eaidence of this transition point o f 38 O C. is found in drop weight measurements. Increasing concentration causes decrease in the drop weight.
With increasing temperature the drop weight increases in more concentrated solutions, but $nally shows decrease until the transition point is reached above which all concentrations show no appreciable change in drop weight. With increasing p H there is a tendency for all concenfrations to. reach a minimum at the neutral point. The drop weight changes slighfly with age of the solution.
EXPERIMENTAL APPmATus-The apparatus used was the Morgan drop weight apparatuslS with the exception that a manometer tube was included in the suction line to give an accurate control during the formation and falling of the drop of liQuid. Cottonseed oil was used in this tube because of its low weight Quinckea records the surface tension of one concentration. This measurement is undoubtedly in error, because the specific and low vapor pressure. The amount of suction used ab gravity of the gelatin solution a t 20’ C. is given as 1.0000, which the time when the drop fell was 0.47 mm. of mercury. is in error. METHODOF MAKINGDETERMINATIONS-The determinaDensity measurements have been made by Davis and Oakes. Zlobicki6 measured changes in surface tension of gelatin solu- tions were made in the usual mannerlo by collectingand weightions with temperature, making only a limited number of meas- ing a given number of drops, and from these the h o p weight urements, and reached a concentration of only 2 per cent gelatin. of the solution in milligrams was calculated. The agparatw
ERY few measurements of the surface tension of gelatin solutions have ever been made, and the few that are recorded cover such a limited range of working conditions that it was deemed advisable to measure the surface tension of gelatin solutions under varying conditions.
V
Bancrofts says, referring to Zlobicki’s work, “addition of 0.5
t o 0.S gram gelatin to 100 cc. water cause3 a marked decrease
in the surface tension of water, while addition of further amounts has practically no effect. In the same connection, Alexander’ says, “0.5 to 0.8 gram of gelatin to 100 cc. of water causes a marked lowering of the surface tension of water although further addition does not increase the effect.”
Consideration of Fig. 2 shows that increasing concentration of gelatin causes a continuous and appreciable decrease in the surface tension of water. Sheppard and Sweets measured the interfacial tension between gelatin solutions and toluene, but have made no measurements of gelatin solutions in contact with air.
The present paper covers an investigation of the variation of surface tension with (1) concentration, (2) temperature, (3) pH, and (4) age of solution. 1 Presented before the Division of Leather and Gelatin Chemistry a t the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 t o 14, 1923. * Contribution No. 8 from the Research Laboratory, National Biscuit Co., New York, N. Y . : A n n . Physik, 10, 607 (1903). 6 J . A m . Chem. SOL.,44, 464 (1922). 4 Bztll. acad. sci. Cracovie, 488 (1900). I “Applied Colloid Chemistry,” 1921, p. 189. 7 “Glue and Gelatin,” 1928, p. 138. a J. Am. Chcm. Soc., 44, 2797 (1922).
10
0 IO 20 30
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40
1 I
1
2
3
4
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7
8
9
1
0
1
1
PH FIG.1-TITRATION CURVE
FOR OSSElN
GELATINNa. 1. 1 P E R
CENT
SOLUTION
was thoroughly cleaned and dried before each determination. During the determination a constant temperature was maintained by use of a water thermostat. 9 J . A m . Chem. SOG., 82, 349 (1911). 10 Morgan and co-workers, J . Am. Chcm. Soc., 80 (1908); 35 (1911): 86 (1913),a series of some twenty papers.
