Results Obtained Using a Rotary Evaporator and a Diaphragm Pump, with and without a Capillary Tube
tally t h a t only a few more minutes are needed to remove 250 mL of dichloromethane a t 35 'C (entries 1-3 of the table). . The use of two to five minutes more is quite acc e ~ t a b l in e the vast maioritv " " of ao~lications k d will be more than compensa'tkd by the increased solvent recovery. When the rotary evaporator is needed occasionally for higher boiling solvents, it is advisable to use the capillary with a bypass as depictedin Figure 2. This bypass consists of a glass valve and two T-connectors. Entries 9 and 10 of the table show that with a higher boiling solvent such as toluene (bp 110 W, the use of a capillary tube is no longer necessary. ~~
Entry
250 mL of solvent used in flask A
Bath temp ('C)
Capillary internal diameter
Time needed to Amount of solvent completely empty recovered in flask B flask A
(mm) dichloro methane
35
none
14min
dichloro methane
35
0.6
I6 min
dichloro methane
35
0.4
t9min
dichloro methane
50
0.6
9 min
dichloro methane
50
0.4
10 min
diethyl ether
35
none
7 min
diethyl ether
35
0.6
9 min
diethyl ether
35
0.4
12 min
toluene
50
none
10 min
toluene
50
0.6
19 min
Experimental Conditions Arotary evaporator (Biichi, Rotavapor-R), cooled with tap water a t 13 T , was used, connected w i t h a d i a p h r a g m p u m p (Vacuubrand, type MZ2C). No vacuum grease was used a t the glass joints. Portions of 250 mL of dichloromethane (bp 40 'C), diethyl ether (bp 35 'C), and toluene (bp 110 'C) were rotovapped from a 500-mL flask rotating in a water bath a t 35 or 50 'C. The duration of the process and the amount of solvent recovered in the rotary evaporator were measured. Two types of capillaries were used with inside diameters of 0.6 and 0.4 mm, respectively, and a length of 5 cm. As a n additional safety precaution, be sure to clamp both flasks on to the rotary evaporator.
Increasing Student Awareness of the flammibility of hair Treated with Hair Spray
Figure 2. Capillary with bypass.
u
and costly, consisting normally of the use of a vacuum controller andlor an additional condenser behind the pump. An extremely simple device, costing less than a dime, can solve the solvent-waste problem. A piece of thickwalled capillary glass tube, 5 cm long, with a n internal diameter of 0.4-0.6 mm is placed in the vacuum tubing between the rotary evaporator and the pump (Fig. 1). I n this way, over 96% of dichloromethane was recovered by the water-cooled condenser inside the rotary evaporator (entries 2-5 of the table). The experiments in the table were carried out with a diaphragm pump having a capacity of 2.4 m3/h. Without the inserted capillary only 30% of the dichloromethane from flask A was recovered (entry 1of the table). Of course, the capillary tube reduces the capacity ofthe pump; therefore, it takes more time to remove all the solvent from flask A. However, it was established experimen-
Richard Poole Athens High School 6 Sunnyside Drive Athens, OH 45701
Recently the safety poster, "Hair today..gone tomorrownl took on added meaning as I saw strands of hair burn and curl to the scalp of a student. Sometime earlier in the day this student had applied hair spray, and, a s she leaned over to light the burner, the spark from the burner lighter ignited the gas from the burner, which in turn ignited her hair. As a result of describing this accident to my students and demonstrating to them the burning of two sheets of filter paper (one of which was coated with hair spray), the safety awareness of this isue has been greatly increased. I n hushed tones, I now hear the students saying a s they are lighting their burners: "Hair today. ..gone tomorrrow". 'Safety tips poster. Michigan Technological University, Houghton. MI 49933.
Volume 71
Number 1 January 1994
55
