Pressure Regulating and Indicating Apparatus for Vacuum Systems BASSETT FERGUSON, JR., Ugite Sales Corporation, Chester, Penna.
F
OR many laboratory vacuum systems the automatically
controlled air leak is the simplest and most satisfactory method of pressure control. Figure 1 illustrates such a n apparatus which has been evolved to eliminate many of the objections to earlier designs of this type of control. This device has proved to be inexpensive, easy t o operate and maintain, and capable of a n accuracy of *0.2 mm. for pressures of 5 to 760 mm.
adjust the frequency of this cycle; six to twelve cycles per minute are satisfactory. When increasing system pressure, or when bringing it to atmospheric pressure after use, it is customary to open stopcock C. If this is neglected, however, the mercury is forced into bulb A as the pressure is equalized, but it then falls back into position in the tube without further adjustment.
With the apparatus set up as shown, stopcock C is opened, switch M is closed, and mercury is admitted through valve D (by means of a leveling bottle) until the mercury just makes contact at E, closing the electrical circuit. D is then closed and M is opened. The s stem is evacuated to the desired pressure a t which point C a n l M are closed. Bulb A maintains the desired pressure and as the vacuum source tends to decrease the system pressure the mercury will rise in the right-hand arm of the Utube, making contact a t E and activatiing electromagnet G, thus opening capillary leak H . The capacity of bulb B and the resistance offered by capillary N cushion the effect of this leak on the mercury. and caDillarv I prevents setting up a harmonic surging of thgmercury, When sufficient air has entered H to increase the system pressure to that of A , the contact at E is broken and the spring flap on G closes H. A needle valve in the line to the vacuum source may be used to
FIGURE 2. CLOSED-END MANOMETER
Oxidation of the mercury by the sparking at E may be decreased by floating a small quantity of oil on the mercury. White Russian mineral oil may be used after shaking with mercury to remove sulfides and filtering. The U-tube may be cleaned readily by draining the mercury from stopcock D and rinsing, by use of a leveling bottle, with dilute nitric acid, water, and acetone successively. The glassware is furnished to Ugite Sales Corporation specification by Ace Glass, Inc., Vineland, N. J. The electromagnet is an ordinary twin-coil buzzer, obtainable a t any electrical supply shop. It is then wired directly to the coils instead of through the make-and-break buzzer as furnished. Dry cells or a direct current source is used. The device may be mounted on a board for convenience in handling.
A closed-end manometer has several advantages over the open-end type for use in vacuum systems. It is independent of atmospheric pressure and obviates the necessity for continual barometric readings and corrections. It is read more easily and accurately, since under increasing vacuum its legs approach a common height, while the reverse is true of the open-end type. The disadvantages of the closed-end manometer are mainly the difficulties encountered in filling the manometer properly, and in removing the mercury and cleaning the manometer.
1 c
Figure 2 illustrates a desi n for a closed-end manometer which overcomes these troubles. &opcock A may be opened and after
FIGURE 1. DIAGFLAM OF APPARATUS 164
,bruary IS, 1942
165
ANALYTICAL EDITION
5cient mercury has been admitted through B, A is attached t o sowce of vacuum, exhausting the air above the mercury in the it-hand column. The dosed arm of the manometer may be ,ated with a Bunsen burner to drive off air adsorbed to the surce of the glass and dispersed in the mercury. Now a slight air pressure is applied at B, forcing the mercury up into stopcock A . When the left-hand column is oompletely Wed with mercury, A is closed. The manometer may be checked against the barometer to determine the success of the filling operation. It should agree with the barometer within 1 mm. at 760 mm., which amounts to
a much smder error at rediced pressure-(e. g., 0.05 mm. a t 40 mm.). For oleaning the entire plug of stopcock A is removed,,and dilute nitric aiid, water, and acetone, consecutively, me crculated through the tube. A constriction at the bottom of the tube cushions pressure changes. A sliding wooden soale may be used to simplify reading the differential heights of the two columns. This glassware ia made to Ugite Sales Corporation speoifioations hy Ace Glass, Inc., Vineland, N. J.
Continuous Washing Apparatus for Solutions in Organic Solvents A. L. LEROSEN, California I n s t i t u t e of Technology, Pasadena, Calif.
0
FTEN it is necessary t o wash petroleum
A
E
H FIGURE 1 (LeJl). WASHINGAPPARATUS A pinohalamp. B waster inlet. B D B C ~ ,E
air a+justment tube, oonstant, washing tube outlet, F solution. 0 wste?, H outlet to dram
FIQURE2 (Righl). MODIFIEDAPPARATUS A water outlet. B water, C solution
tliua,
V ~ U O ~ I G ,
chloroform, etc., solutions free from a water-soluhle solvent, alkali, or acid. If many solutions must he washed the operations are tedious and time-consuming, but these difficulties may be eliminated by the device shown in Figure 1. A constant air space is maintained in a separatory funnel while a stream of water is passed through the solvent. To operate, water is added t o the solvent mixture. After this first wash water is drained off as usual, the washing tube is inserted with pinchclamp open. The water is then turned on at a suitable rate and when the upper layer has reached the mashing tube outlet, the pinchclamp is closed and the s t o p cock is opened. The closed air space maintains a constant level, so that the quantities of water entering and leaving are always equal. This washing is continued as long as neoessary-e. g., 5 to 10minutes for ligroin plus alcohol in a 500-cc. funnel. Then the bottom stopcock is closed, the pinchclamp is opened, the washing tube is rinsed with some pure solvent, and the water stream is stopped. This procedure has given satisfactory results with volumes of solvent from a few cubic centimeters up t o 8 liters. The setup used in this laboratory, a series of 8 units, is shown in Figure 3. For liquids heavier than water the washing tube is slightly modified (Figure 2) and reaches near the bottom of the separatory funnel. The water flows out at the top through B glass tube. The stopcock remains closed until the washed solvent is drawn off. No air pocket is present in this case. C r m a m d crrilin
hhoratnries of Chemiatrv. California Institute of Tsoh-
