Filtration of Hot Solutions G. R. YOHE, Ohio Wesleyan University, Delaware, Ohio
T
HE problem of filtering hot concentrated solutions in re-
factory with water and benzene solutions. In one test experiment an asbestos filter was used with a strongly acid, concentrated solution of sodium hydrogen sulfate; this solution fdtered very slowly, yet no dificulty was experienced in keeping the temperature (measured in the funnel) a t 70" to 75" C. for the several hours required for the filtration. The device has the advantages that it heats not the funnel but the solution being filtered, and that it automatically keeps the funnel filled and therefore requires attention only a t the start and a t the finish of the filtration.
crystallization processes is sometimes perplexing, for the solution in the funnel and the main part of the solution must be kept hot to prevent premature crystallization. The use of a jacketed funnel is common, but not too satisfactory when large quantities of rather slow-filtering solutions are being handled (1).
The design of this apparatus may be varied. The section at
D may be inclined, and a free flame used as the source of heat if
nonflammable solvents are used. The writer has used a jacketed tube with steam heat for bennene solutions, but the electric heating unit seems most satisfactory for a11 pur oses. Constant level is maintained in the funnel fecause air is not admitted to inverted flask A until the level in the funnel goes below the end of tube B. Working on the thermo-siphon principle, the coolest of the solution in the funnel is withdrawn through tube C, heated at D,and returned to A . When the level in the funnel falls below the end of B, air enters here, and the flow of the liquid throu h the heating coil is temporarily reversed. This does no harm. &re must be taken to see that the stopper in flask A is securely in place. In constructing the heating unit, D,the glass tube is covered with thin asbestos paper, then wound with No. 26 chrome1 wire (resistance of heating coil about 10 ohms), and covered with asbestos insulation. It has been found that a current of about 2 to 4 amperes results in satisfactory heating.
C -
FIGURE 1. DIAGRAM OF APPARATUS Literature Cited The device described here is of service in filtering large volumes and keeping the solution hot with a minimum of attention from the experimenter, and has been found satis-
(1) Caldwell, J. R.,IND. ENG.CHEM.,Anal Ed., 7, 76 (1935). RECBIVED March 13, 1935.
A Simple Laboratory Stirrer for Use on the Vacuum Line GEORGE T. AUSTIN, 311 East Armory Ave., Champaign, Ill.
ITu'
LABORATORY work with small quantities of organic chemicals, it is frequently necessary to stir for extended periods of time. For' laboratories not having pressure lines, the vacuum stirrer shown above will be found very convenient. It is extremely inexpensive, requires little time to make, and is powerful. If carefully made it will stir viscous liquids, and is especially applicable for use in the synthesis of the Grignard reagent. For schools, it is very handy for students in second-semester organic work, where it is inadvisable and expensive to place electric motors in their hands. The housing is a small can, such as is used to contain chocolate. The tin blades for the vanes are made from any sheet metal, and may be soldered together and fastened to the shaft with de Khotinsky cement, or any other available wax. The fitting between the shaft and the bearing should be tight to prevent leakage of air, and should be lubricated with Iight oil. The use of a nozzle on the air inlet increases the power greatly. A second air inlet will increase the power. A little variation in the size of the opening will lead to better results. The connection of the shaft to a longer one is accomplished by means of a rubber policeman. For use in potentiometric titration, or where a mercury seal is not required, the shaft may be an unbroken rod with the propeller sealed upon the end as shown in Figure 1.
& C
To vacuum
Air inlet
line
FIGURE 1. DIAQRAM OB STIRHER A, B C. Best types of agitators f d w e with this stirrer D. Small tin can E. 3-mm. +,sa rod F. de Khotinsky cement
RECEXVBD Maroh 12, 1935.
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G. H. I. J.
Sheet-ateel vanes Two small washers 5-mm. tubing No. 11 rubber stopper
