Joseph B. Lombardo
American Cyanamid Company Bound Brook, New Jersey 08805
Automatic Filtration Cell for Solubility Studies
The most troublesome step of the usual solubility determination, especially when far-from-amhient temperatures are involved, is the sampling procedure with the concomitant filtration. Vessels have been developed in this laboratory which automatically and continuously take care of this filtration step. The device is illustrated in the figure. It is fabricated entirely of horosilicate glass, starting with a filtration tube of suitable porosity and dimensions-such as S.G.A. No. F-3800 (Scientific Glass Apparatus e Go., Bloomfield, N. J.). The filter porosity is deter. mined by such factors as .+= 7 solvent viscosity and solute particle size. Di? @ & & mensions are determined 1 bv the amount of s a m ~ l e , ,I or solvent available and the solubility expected. A I convenient and versatile size is that made from 25-mm-diam. tubes with the height of each leg approximately 10 em. A standard taper outer joint, such as S.G.A. JJ-2400, ~7 24/40, is attached to the \ ' upper part of the filter
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journal of Chemical Educafion
tube (side A of the figure) while a similar joint becomes side B. In use, some appropriate amount of sample is transferred onto the filter on side A and a selected amount of solvent added, also on side A. Hose adapters, such as S.G.A. JA-2550 or JA-2790 are inserted in each of the two joints and a hose attached to each. The U-tube is immersed, up to the ground-glass joint, in a thermostatically controlled bath. The hose from side A is connected to a pulsator; the hose from side B is connected to a drying tube, cold trap, or isolation balloon, as conditions require. The time of equilibration is determined either by experience or by taking repeated samples until replicate analyses agree within prescribed limits. After necessary pulsation time has elapsed, a portion of the solution is rapidly poured out of side B for analysis. If extreme temperatures or solvent properties are involved, special techniques-such as opening in a dry box or filling a glass a m p o u l e m a y have to he applied. The pulsator consists of any source of intermittent air-pressure change, which can serve as an air-vapor piston to send the solution oscillating through the filter disk and hence through, and in intimate contact with, the solute. I n this laboratory we have used a geared motor turning a cam a t 2 rpm which imparts oscillatory motion to a spring-loaded plastic bellows which in turn alternately compresses and expands air in side A. If necessary, an inert gas can he substituted for air.
