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.
...
"..~
_...
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
163
I
~
I
ANALYTICAL CHEMISTRY
164 marked on the cylinder along side the 20-cm. mark. I n use, it is desirable that all the cylinders in any one test have substantially the same dimrnsions-e.g., hold the same volume up to the 20-cm. mark. When calibrated, the cylinders generally held from 185 to I95 ml.; the greatest number held 185 ml. A pulley wheel is attached to the end of one of the axles, and also a handle for manual turning. Manual turning has been found to be quite sufficient for all ordinary comparisons; however in some cases it might be desirable to use a constant-speed motor attached to the pulley wheel. T E S T METHODS
Concentrated Emulsions, containing 10% or more of oil phape. EMULSIFIABLE COXCENTR.4TES HEAVIERTHASWATER. The emulsifiable concentrate is measured directly into the bottom of the glass cylinders, then the water used is added slowly down the side of each cylinder so as to leave the concentrate as a discrete layer beneath. A small amount of emulsion almost invariably forms a t the interface, but the two layers must. be clear. Keeping the frame slightly tilted aids in this operation. Afterward, the tubes are stoppered (No. 7 rubber stoppers or corks may be used) and the frame is closed and tightened. Rotation of the frame 10 to 20 times then forms all emulsions simultaneously, except for the traces of emulsion which formed during the previous operation. Comparisons are made a t convenient time intervals thereafter-for example, 1, 5, and 10 minutes, 1 hour, and 21 hours. If it is desired to take numerical readings of creaming or sedimentation rates, a thin strip of millimeter paper may be cemented to the side of each cylinder and readings taken from this. EMULSIFIABLE COSCENTR4TES LIGHTERTHANFvATER. The procedure is exactly as described above, except that the water is measured into the tubes first, then the emulsifiable concentrate(s) are measured carefully onto the surface of the water in each tube. DENSITYOF EMULSIFIABLE CONCESTRATE 1s EXACTLY 1.000. It is desirable to run a preliminary test a t room temperature to see whether sediment rises or falls. Either may occur through slight composition changes in the two phases. Thereafter bv raising or lowering the temperature a t which the test is run, it should be possible to carrv out the test as described for the two types above. Dilute Emulsions, containing 2% or less of oil phase. The emulsifiable concentrateis) are measured into 5-ml. Griffin beakers, which in turn are floated on the surface of the water used in the respective cylinderfi. The cylinders are stoppered, the rack is closed and tightened, and the frame turned through 10 to 20 rotations, as before. If the volume of the concentrate is less than about 1 ml., it is necessary to weight the bottom of each beaker to prevent tipping. This may be done by cementing a small disk or metal washer to the outside. I n use, the beaker almost invariably comes to rest in an upright position on the bottom of the emulsion tube. In the rare instance when one does not, i t can nearly always be righted by allowing all the beakers to fall through one more complete revolution. Turning the rack to an angle about 30” with the vertical, then allowing it to come to rest in vertical position, causes all the beakers to move to one side, after which sedimentation rates are observed from the other side. Since the vertical edge of each beaker occupies a relatively small, nearly constant area, it does not interfere seriously with reading of sedimentation rates, even though aome of the sediment falls inside the beaker. Wettable Spray Powders, suspension and foaming. The powders are weighed directly onto the surface of the water. It is desirable to weigh the powders first, then drop them all into the cylinders containing water, a t as nearly the same time as possible. The cylinders are stoppered and frame is closed, tightened, and rotated 20 to 30 times (more if necessary to break up agglomerates). If foaming is to be compared, it is desirable to fill the tubes only about half full and use vigorous agitation (rotate the frame quickly for about 30 seconds). Re-emulsification and Resuspension. These qualities may be determined after a suitable time interval by rotating the frame again and noting the number of complete revolutions necessary to resuspend or re-emulsify the sediment, in each case.
-4typical example is shown in Figure 1; the emulsifiable concentrate in tube 1 was added slowly down the side of the tube into the water 3 minutes before agitation, while the same concentrate in tube 2 was added to the floating beaker; thus, introduction of concentrate into the water was simultaneous with agitation. Otherwise the two emulsions received identical treatment (experimental details appear in Table I ) . This does not appear to be a problem with emulsions containing IO’% or more of oil phase, when evaluated as described above, and may not be a problem with all emulsifier-solvent systems. The range between 1% oit phase and 10% oil phase is doubtful.
Table I. Tube S o 1
Details of a.Typical Comparisonn
Water Used Tap
Hardness (as CaCOd. P.P. M , 40 (approx.)
Method of Adding Concentrate .Idded down side of tube 3 minutes before agitation Added t o floating beaker Added t o floating beaker Added t o Boating beaker Added t o floating beaker Added t o floating beaker
40 (approx.) Tap 0 Distilled 250 Artificial hardb 500 5 Artificial hardb 6 .Irtificial hardb 1000 a Results shown in Figure 1. b Equal moles of calcium chloride and magnesium chloride
2 3 4
LITERATURE C I T E D
Griffin, W. C., and Behrens, R. W,,
.\N~L.
CHEY..24, 1076-8
(1952).
Kelly, J. A., J . A g r . Food Chem., 1, 254-7 (1953). Sela, E., Ibid., 1, 381-6 (1953). Suggitt, J. W., “Procedures for Evaluating Herbicides,” presented before Agricultural Pesticide Technical Society, Xacdonald College, Quebec, Canada, June 23, 1954.
Trap for Attenuating Mercury Vapors in the Mass Spectrometer B. 1. Tuffly and W. J. Lambdin, Carbide & Carbon Chemicals CO., Division of Union Carbide & Carbon Corp., South Charleston, W. Va. HE
presence of mercury parent peaks a t m/e 198 to 204 and of
Ttheir half-peaks a t m / e 99 to 102 has caused difficulty in the interpretation of some mass spectra. Mercury in the ionization chamber of the Consolidated mass spectrometer Model 21-103 arises from three different sources: the manometer in the gas inlet system, the diffusion pumps in the exhaust vacuum unit, and the mercury orifice (liquid inlet). Mercury vapors from the manometer of the gas-inlet system are
n-
-32 X 90 mm VESSEL
DISCUSSION
Where dilute emulsions containing 1% or less of oil phase are evaluated, it has been the experience of the author that variable and erratic results are obtained when there is a delay between the introduction of the emulsifiable concentrate into the water and agitation of the mixture While believed to be due to extraction of part of the emulsifying agent by the water before agitation, this effect has not been investigated beyond establishing that it exists.
Figure 1. Diagram of Trap
