A Simple and Efficient Filtering Tube
William M. Thornton
Journal of Industrial & Engineering Chemistry
pipe of the hydrogen sulfide main, thin-walled, gum-rubber tubing one foot long and of convenient diameter is attached. Near the branch pipe, and inside the rubber tubing, is a glass "pearl" made from glass tubing of a diameter slightly larger than that of the rubber tubing-the rubber should not be stretched too much. The device is merely another application of a similar device that is used with ordinary Mohr burettes. .Longitudinal C/o sed I n use cross section The advantages of the device are
... obvious: the stu-.dent must "be on his job;" open stopcocks are impossible; the flow of gas can be regulated with certainty and extreme ease; the device is not easily put out of order; it is easily and quickly replaced; there is no prolonged, excessive squeeze; the pearl may be moved t o a new position when necessary; the cost is ridiculously low; the gas is not wasted. The device has been in use only one month and, consequently, it is too early to say that it is an entire success where the durability of the parts is concerned. Where its use by the student is concerned, there can be no question of its entire success; its simplicity, and t h e ease and neatness of its manipulation make a "hit" with the student. Undoubtedly improvements in design and material are possible. The apparatus here depicted was designed particularly for handling those precipitates whose solubilities are sufficient t o necessitate great economy with t h e liquid used for transferring and washing. Although it resembles somewhat the filtering devices of Zopfchen2 a n d of Bailey,3 it is not, however, identical with either. Moreover, the appliance can easily be put together from materials to be found in any well-equipped laboratory. A straight glass tube, having a stopcock a t its mid-.die point, is sealed to a carbon filter tube. The latter 1 Published by permission is fitted with a two-hole rubber stopper. The stem of a Walter crucible holder passes through one hole of the stopper while the other contains a right-angled exit tube. The rubber hose leading t o the suction pump is intercepted by an ordinary T-tube, the free end of which is joined t o a short piece of rubber tubing. A Mohr clamp is kept in readiness. The whole is held in position by a stand with two clamps appropriately placed-one t o grasp the main tube and the other t o support the T-tube. The manipulation is quite obvious. Having prepared the asbestos felt in the regular way, the perforated crucible G is set in the collar W . After the suction has once been adjusted, it need not be interrupted throughout the entire filtration. When the cock S and the clamp M are closed, the carbon tube C serves the purpose of a small filter flask. When the clamp M is opened and pushed upward past the shoulder Qn to the tube t , atmospheric pressure is restored within the apparatus (or nearly so); and then, on opening the cock S, portions of the clear filtrate can be delivered into the original beaker. The cocks I I U are then closed, and, after the usual application of the "policeman," the liquid is again poured over into the perforated crucible G. These operations can, of course, be repeated as often as may be desired. With the aid of the above-described outfit, the author succeeded in transferring and washing a certain precipitate (the washing being accomplished by four small portions of iced water successively applied) so that the sum'total of the filtrate and washings did not exceed 2 7 cc. Furthermore, the apparatus is so convenient that filtrations can be very quickly performed with its help-thus reducing to small dimensions the losses incurred in handling those precipitates which suffer an increase in solubility on rise of temperature.