All-Glass Valve for Cannon Automatic Dispenser. P. L. Hoogland, -4tlantic Fisheries Experimental Station, Halifax, Xova Scotia, Canada. microbiological assays, the Cannon Automatic Dispenser (International Instrument C ' o , , P.O. Bos 7781, Los.2ngeles 15, Calif.) has proved useful. The appara>us consists of a constant pressure device, a magnetic valve assemhly, and a timer: FOR
The fluid to be dispensed is forced from its container by coinpressed air. The pressure is kept constant by means of a contact manometer operating a vent. The fluid then passes through a magnetic valve which may be opened and closed by an electric timer. The essential part of the timer is a metal disk mounted on the shaft,of a synchronous motor, rotating with about 6 r.p.ni. The disk is covered with polar-coordinate paper. from which segmente with different angular openings can be removed, thus providing for a sequence of metal and paper alternately. .4 metal clip is pressed lightly against the disk; when the disk turns, an electric circuit will be clowd as long as the clip touches metal and opened when i t touches the paper. This time switch, through a relay, controls the intervals during which current passes through the solenoid of the niagnetic valve. The valve consists of rubber tubing, closed by a knife-edge which is pressed against' it, with coil springs and opened n-hen the solenoid is energized. With t h k apparatus predetermined sequences of diffeent volumes;. as well as of constant amounts, may he delivered. These sequences may he selected h y choosing the proper openings i n thr paper disk of the timrr. TWO difficulties were encountered: The reproducibility of amounts delivered dep(in(lson the condition of the rubber tubing of the magnetic valve. and the position of the knifr-edge of the valve on the ruhber tulling determines whcthei or not there will lie .I lineal relationship lwk e e n the amountq 01 fluid delivered and the length of time during which themagnet is actuxted. ..\ slight changr i n this position may cauq(l relativel\- large changein t h e r e l a t i o n s h i p . Both, a t times, v e i f > found to interfere sei iously with reliable operation of the dispenser. The original valve assembly was therefore replaced by one of a l l - g l a ~ ~ construction (Figure 11, ID 3 OD 9 N hich obviates these difficulties. The plunger of the valve is made by fusing one end of a 9-mm. Pyrex No. 7740 glass tube. 30 cni. long, intoawedgeshaped tip. The tip ie then ground t o fit the seat of the valve housing \Then a water-tight sea1 is obtained, the tubing is cut off to 8-cm. length, filled with soft iron wire, and sealed a t the top.
ID 2 OD 7
Figure 1. I.D.
All-Glass Valve
Inner diameter O.D. Outer diameter Dimensions iu millimeters
The tapers of the valve and its socket do not seem to be critical, as excellent results were obtained with various models; in the apparatus now used, the tip is a cone with an 80" angle and the seat has an angle of approximately 90". Further dimensions are shown in Figure 1. The end of the interchangeable tip is constricted to the desired size (depending on the amount of fluid to be dispensed and the working pressure) and fire polished. The spring hooks on the top part, of the T10/30 :oint should be bent upward slightly, so that they may pass through the core of the coil when the valve is being assembled. The coil terminals are connected directly to the middle receptacle of the timer for dispensing, or to the upper receptacle for titration. The side tube is connected to the container for the fluid that has to be dispensed. To fill the valve assembly this, fluid is forced slowly through the side tube, while the valve plunger is down and the stopper opened. The stopper is closed as soon as the liquid level reaches it. The overflow arrangement takes care of small amounts of fluid that might run over the top of the valve housing. The magnetic coil is then actuated briefly to fill the apparatus completely. Precision. With the time switch set for a sequences 1-23-4-5, a tip nidth of approximately 0.3 mtn.. and a working pressure of about 120 nim. of mercury, the srquence 1.00-2.003.004.00-5.00 ml. of water \vas delivered i n 10 seconds. 111 repeated determinations, the difference bet'ween each individual amount dispensed and the amount calculated from the averagc' of the sequence was never greater than 0.4%. The error in the delivery of each individual amount was smaller than 0.470, The advantages of the valve over the original type includr greater reliability and precision. As the fluids to be dispensed are not in contact with any material other than glass, the unit can be used more universally. Bssembling and disassembling the valve do not impair the reliability of its operation; this is of particular importance when the unit has to be sterilized. Changes in volume delivered, even over a range of one order of magni.tude, are made by interchanging the tip only and do not necessitate dismantling the whole assemhly. The valve is rigid and can be cleaned easily.
Micro-Kjeldahl Distillation Apparatus. D. J. Jenden and D. B. Taylor, Department of Pharmacology and Experimental Therapeutics. I'niversitp of California, 1Iedical Center, San Francisco 22; Calif. -tillation apparatus described in this paper was designed THE. foi di' use in solubility tests on protein solutions (Falconer, Jenden? and Taylor, Disrimions Faraday SOC.,in press) in which the large number of nitrogen determinations demands speed and masimuni accuracy. 113th these factors in mind the size of the apparatus (swept volume 175 ml.) was scaled down (Figure 1); the smaller swept volume (38 ml.) and surface available for condensation render the steam about tnire as efficient in washing the apparatus clear of ammonia.
At the point of entry of steam into the digest, A , there is a small constriction in the tube in which is seated a conical piece of ribbed glass rod, so that the steam is forced under slight pressure through a circle of small holes (inset, Figure 1). This provides a further increase in efficiency, by producing more turbulence, thereby increasing the surface available for ammonia e+ cape. The rate of escape is increased nearly five times. The steam trap, B, was introduced a t this position because it is functionally most efficient here. Steam and ammonia pass easily t,hrough it to the condenser, but any water condensing in the trap flows quirkly back into the digestion flask. It is im-
