LETTERS To the Editor: When using aspirator pumps the water splashing has always been a nuisance. A simple method to prevent this is to remove the asbestos from a 4 X 4 in. wire gauze, asbestos centered. Press the wire into the drain outlet to raise the center of the wire. Place the wire in the sink directly under the aspirator and the splashing will be a t a minimum. DANIELBORYTA
T o the Editor: In the June, 1950, issue of THIS JOURNAL, Morimoto and Kahn' described simple equipment to make cmrier-free radioactive lead 212 (thorium B). They use solid thorium hydroxide as a11 emanating source and collect the thorium B in an electric field. Some years ago, we described another method for making carrier-free thorium B, which is even simpler.2 The method consists essentially in passing a current of air through a sinter into a flask containing a saturated solution of thorium nitrate in equilibrium with its decay products. The air takes up some of the thoron and then carries it through a second flask filled with dilute acid. Part of the thoron dissolves in the acid and decays there (half life 54.5 sec) to give first shortlived thorium A and subsequently thorium B. I t was shown that in the given set-up a velocity of the air current of about 5 ml/sec gave optimum yield. Activities of the thorium B of the order of lo5 disintegrations per minute can be obtained easily. This is more than sufficient for most demonstration experiments and for much research work with radiolead. However, if even greater activities were desired, these could be obtained by using as the source of thoron not ordinary thorium but either radiothorium or mesothorium in equilibrium with radiothorium. In these cases, the production rate of gas per ml of solabion could be much higher than with the natural mixture of thorium isotopes. E. BRODA .~ICORGANISCH- UND PHYSIH~LISCH-CHEMISCHES INSTITUT DEE UNIWRSITHT W ~ R ~ N GSTMSSE ER 42 VIENNAIX, AUSTRIA
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'Mo~ndom,E. M.,
AND
KAHN,M., J. CHEM. EDUC.,36,
296 (1959).
BRODA, E., FABITSCHOWITZ, H., AND SCH~NFELD, T.,Monafsh.Chem., 83,482 (1952). 530
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Journol of Chemical Educotion
T o the Editor: As a result of many demonstrations of "The Nylon Rope Trick" (J. CHEM.En., 36, 182 (1959)), there has been devised a variation of this polycondensation rsprri~uentw11ii.h is dynnmic :~ndy!r dors nor rrquirc wirding drviccs. I t is continui~usand srlf-propclled. A satisfactory way to get a spontaneous flow of film is to conduct the collapsed film from the center of the vessel over a glass rod or tube and then out and down over a second rod. A fall of about three to four feet is necessary for the film to flow continuously. The required height depends on the size of the vessel, the solvent and reactant system, and the distance of the aqueous surface from the guide rod. Figure 1 shows a simple way of arranging guides from wire and medicine droppers. The main requirement for easy flow is a very smooth inert surface. The length of time during which the film will form continuously depends on the components and the physical dimensions of the system. A preferred recipe is 1.5 ml sebacoyl chloride in 50 ml perehloroethylene and 2.2 g hexamethylenediamine and 4.0 g sodium carbonate in 50 ml water. These reactants in a 200-ml tall-form beaker (2'/a in. i.d.) will produce film for 8 min at about 14 ft/min. Speeds up to 60 ft/ min can be obtained by allowing the rope t'o fall a greater distance. The flow of rope can be stopped by pushing it to the ends of the guides or against the wall of the beaker or by reducing the length of overhanging rope. The flow can be resumed by centering the rope on the guides and giving it a pull.
-AQUEOUS PHASE
Figure I
Figure 2. Side view of apporotus for continu. our polymerirdion.
For the purpose of a long exhibition the process can be continued by arranging separatory funnels and tubing as reservoirs from which to replenish the phases. The feed line for the lower phase should not go through the interface. It must enter through the wall of the vessel below the interface or be cemented smoothly to the inside of the vessel so securely that no liquid goes behind it. An alternative arrangement is shown in Figure 2 wherein the aqueous phase is placed inside a large open tube supported in a somewhat larger vessel containing the organic solvent. Both phases may then be replenished externally. PAULW. MORGAN STEPHANIEL. KWOLEK
