AIDS F O R THE ANALYST point, the valve is opened and alkali flows. When the end point is reached, the circuit is inactivated and the valve closes, stopping the fluid flow. The amount of liquid that passes through the valve is measured by timing the calibrated rate of flow under a constant pressure head. If this valve is used in conjunction with a buret, the volume delivered may be read directly.
Electromagnetic laboratory Valve 8. P. McKay and Charles H. Eades, J?., Department of versify of Tennessee, Memphis, Tenn.
of fluid flow is au important factor in many lahoTratorycontrol operations. An electromagnetic has been deHE
d v e
The possible appliestions of this valve are many. I t is easily constructed, greaseless, easily cleaned, and fast acting, and can he adaioted t o automatic or remote control.
veloped in these laboratories in connection with an automatic recording titrator [Eades, C . H., Jr., McKay, B. P., Romans, W. E., and Ruffin, G . P., ANAL. CHEM,,26, 123 (1954)l for the control of alkali flow to the titrating mechanism. The valve is automatically opened and closed by remote control.
Simplie Apparatus for Comparing Emulsions and Suspensions D. A Pearca, Green Cross Products, Montreal 22, Quebec, Canada NUMBER
of methods of evaluating emulsion stahility of
A emulsihle concentrates have appeared in recent literature.
Griffin and Behrens ( 1 ) described a device by means of which a large number of emulsions may be compared under uniform lighting conditions. Kelly ($) described B method of evaluation of the emulsion stahility of herbicide formulations. Sels (3) listed and described B number of the methods in current use. Suggitt (4) stated (with regard to emulsion characteristics of emulsifiahle concentrates): "For routine evaluation the simpler procedure of comparing the results obtained against a standard formulation is more rapid and meaningful than any absolute method." The apparatus here described was designed with the objects in view of preparing several emulsions (or suspensions) simultaneously for direct c o m p ~ s o nand comparing the emulsions or suspensions in the same apparatus in which they were prepared. This, in the author's experience, has resulted in a definite saving in time and manipulation; in addition, the test method is truly comparative.
3 of 8 polystyrene barrel fitted into T Type No. 4-AC 115-volt alternat-
ityrene side-arm inlet tube, I/, inch h in inside diameter, is cemented t o the plunger harrkl. ' -The outlet tube, E, I/& inch in outside inch. The valve seat of the outlet diameter has a bore of tube is smoothly turned on a lathe to ensure a flat seat. The plunger of the valve, B, consists of B chrome-plated steel rod with 8 reduced diameter near the valve seat end. This permits inlet head-pressure to give increased speed and positive closure to the valve. The part of the plunger that hacks ped C is also reduced slightly in size to permit proper flow of fluid to outlet E. A small piece of foam rubber, a,,acts as a closing spring. Fast positive closure of the valve is achieved by the combined action of this foam rubber, the weight of the steel plunger, and inlet head-pressure acting against the back of the valve seat. A small piece of smooth-surfaced (chemical-resistant) rubber, C, serves as a valve seat. For easy cleaning and decontamination, the top of the plunger barrel is fitted with a threaded cap and neoprene gasket. The valve has fast, positive action with 40 volts alternating current supplied to the solenoid coil. This is ohtrained with a 175-ohm 20-watt resistance in series with the coil and 115 volts alternating current applied t o the circuit. The valve may be used in continuous duty applications with no significant rise in temperature. For intermittent duty cycles where the onperiod does not exceed 5 minutes and the off period is a t least 10 muutes, 115 volts alternatingcurrent may be used on the coil. In operation the valve is actuated by a line-operated pHsensitive controller. When the pH of a sample of acid in contact with a glass-calomel electrode System is below the preset end
Figure 1. Typical Comparison Using Apparatus Described All emulsions contained 1% by volume of one emulsifiable coneentmte. Concentrhte contained (by weight) 25% techniosl grade DDT, %!7 E990 heavy aromatic nauhthh and 4% Emool H-77 emulsifier. Emulsions were allowed to Stand 24 ho&s for maximum photographip effeot,; hoverer, diiierenoes between emulsions were readily apparent by inspeetion 8 8 little 86 5 minutes after agitation.
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As sl.V..,. ~, rl.lll. ....r.i wooden frame supported on a bearing a t each end, in which up to six giass cylinders may be fastened. The emulsions are prepared in the glass cylinders. The cylinders used were those described under Fisher Scientific Co. Catalog No, 8-535. These are plain, ungraduated glass cylinders, approximately 10 inches in heigh!, with flared base and approximately 1.5 inches in internal dlameter. They N W ~calibrated by marking each cylinder a t an arbitrary height of 20 em. from the bottom of the inside of the cylinder, and then measuring the amount of water which the cylinder will hold up to the mark. This value, in milliliters, is
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