NOTES ON ANALYTICAL PR A
CEDURES
Simple Automatic Medie A. A. ANDERSEN
Western Regional Research Laboratory,
Figure 1.
U. S. Department of Agriculture, Albany, Calif.
Automatic Media Dirpenrei
T
HE mtomatic media dispenser shown in Figure 1, which has
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i
been constructed in this laboratory from inexpensive parts, embles an operator to dispense media a t many times the speed of hand work. The essential parts are a 20-ml. syringe with tip end removed, a svstem of valves and tubes (Figure . _ 2). a driving- mechanism. and stable mounting. The barrel of the syringe was cut a t the aero mark. The open end was connected by means of a rubber stopper to a valve system, which consists of a glass T and two check valves cut from No. 2 rubber stovvers BS fihown in Figures 2 and 3. (The vnlves
be calibrated and a new scale placed on the barrel of the syringe to indicate the amount delivered. The syrinrc holder is held in place with two screw8, one countersunk and one round-headed with washer, which allow the syringe to be properly aligned with the drive shaft. This alignment is important for smooth operation and ia obtained by p u m p ing a few strokes with screws loosened and then tightening the screws. The driving mechanism consists of a. 12.5-em. (5-inch) hardwood wheel, with an adjustable slide for regulating delivery a 0.6-ern. (0.25-inch) steel-jointed drive shaft about 45.5 cm. (19 inches) long, and a errtnk or motpr or both. The drive shaft is attached to the syringe plunger wlth a double horseshoe coupling fFieure 3A). which is readllv removed when rt is necessary to flush &'from tG syringe. The dispenser can he operated by hand or by motor. Hand operation is fairly satisfactory for most routine work: however. a small motor with gear reduction and pulley to give proper speed (25 to 40 strokes ver minute) is desirable, especially if a large Figure 9.
Valve Anembly
463
INDUSTRIAL A N D ENGINEERING CHEMISTRY
464
pear-reduction unit is about $10. The h t e p pulley was cut from menni of B fib,&hiretlie stopper WaS rotated on n .ihnfr. The S I L C of stopper will drpend upon rhe snccd of the motor. The soeeil o i the u n i w n i i l motor is also kntrollable by variation of Goltage.
k So, C, rubber 9lopwr. by
With uniform speed the volumes delivered are reproduced with remarkable accuracy, which has heen determined by weighing random deliveries in stoppered bottles. The tabulation below lists typical results on deliveries of 20, 10, and' 2 ml. of water. Deliveries of air were found to be similarly reproducible. MI.
Mi.
MI.
20.02 20.00 20.00 20.00 20.01
10.00 10.00
2.008 2.001
9.99 9.99 9.99
2,002 2.008
2.005
Vol. 17, No. 7
Any common liquid or gas that does not attack rubber or glass ean be dispensed in the apparatus. Practical sterilization of the apparatus can be obtained if both intake and delivery tubes are placed in a flask of boiling water and the machine is operated a few minutes. The syringe, valve system, and tubes can be wrapped in a towel and sterilized in an autoclave. Parts are easily cleaned or replaced, After agar medium has been dispensed, cleaning is effected by prompt circulation of hot water through the device. The apparatus can be used to aerate fermentations or to circulate liquids or gases in closed systems. Used as a vacuum pump, i t creates pressures of 8 to 10 cm. of mercury. When turned by hand i t serves particularly well as a filter pump. The type of valve employed has still other uses-n wash bottles, filter pumps, and vacuum lines to prevent backflow.
Magnetic Easel for Use in Spraying Test Panels T. H. GLYNN MICHAEL Paint Research Laboratory, National Research Council, Ottawa, Canada
I
N ALL paint research and testing laboratories, small test panels are continually being sprayed. None of the normal methods for suspending these panels during spraying is satisfactory. Hanging the panels on nails, supporting by adhesive tape, and bolding in wooden guides have all heen tried, but all are time-consuming and each has some drawbacks.
Figure 2.
I n order to overcome the difficulties involved, an electramagnetic easel was built for this laboratory. This principle has heen used for holding tinplate panels in a horizontal position during the production of drawdowns ( l ) ,but i t does not appear to have been previously used for holding panels during spraying. The instrument (Figure 1) consists of eight horseshoe electromagnets, wound ou soft steel cores, which are mounted with th(! free ends of the poles flush with the working surface of the easel. The magnets are boxed in behind the easel and the whole is pivoted an a horizontal axis, so that it may he swung to the ndrmal 70" spraying angle. The electromagnets are connected in parallel, and supplied by a 110-volt direct current line. If direct current is not available, magneta suitable for alternating current use may he wound on laminated cores. A sketch of the instrument, indicating the dimensions and the
Diagram of Easel
electrical circuit, is shown in Figure 2. Siee and number of electromagnetsmay he modified to meet individual requirements. I n use, the easel is placed horieontally, covered with a piece of kraft paper, and the necessary test panels me laid upon it. The current is then switched on, the easel turned to the appropriate angle, and the spraying carried out, The easel is then returned to the horizontal, the current turned off, and the sheet of kraft paper bearing the panels transferred to a piece of wallboard which is set aside during drying. The easel will hold the panels firmly in place against 40 pounds air pressure a t the gun without any movement, requires no drilling or other preparation of the panels, does not mask any part of the panels, and leaves the backs clean for subsequent coating if necessary. LITERATURE CITED
(1) Cranmer. Adarns, and Gottfried, Am Paint J . , 28, No. 44, 44 (1944). N.R.C. No. 1292.
