DISPENSING LABORATORY SOLUTIONS CHARLESF. ECK~LS, C O ~ OUNION N JUNIOR COLLEGE, COMPTON, CALIFORMA
The effcient distribution of reagents and solutirms in school laboratories requires safety, economy, and convenience. Three devices for different kinds of solutions are suggested. For acid and base reagents a glass siphon with a 4-mm. plug bore glass stopcock at the outlet may be used. The liquid flow is easily and conveniently controlled without w s t e . For special solutions a 150-cc. pipet bulb may be used to force the solution out of a 2.5-liter bottlefitted with a glass spout. Only glass to solution contact makes this &ice useful when purity is to be considered. For indicators a n accurate control of drops i s necessary. A buret with a glass bead in the rubber connections to the drawn glass tip makes cureful control possible.
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Inefficient methods of distributing reagents and solutions in school laboratories are the cause of much waste of time and materials. Frequently strong solutions are spilled on school property or students' clothing with seriRubber ous damage to both. Some schools pay Stopper an assistant to keep the student reagent bottles filled, but the students are left to help themselves to the special solutions. Safe methods of dispensing all types of solutions would allow the responsibility to be placed on the student with a saving of time and money. Three easily assembled devices, which have been used successfnlly, are here suggested. Dispensing Acid and Base Reagents
Lead
+strap
Each student has the use of eight 16oz. glass-stoppered reagent bottles which Cork are to contain concentrated and dilute mom 1 HeSOh, HNO,, and HCl and dilute NaOH and NH40H. For each of these small bottles a large 2.5-liter bottle (those used to ship small amounts of acids and bases) is placed on a main shelf in a convenient place. The bottle is fitted with a glass siphon, as in Figure 1, made by welding a 4-mm. plug bore glass stopcock to pyrex tubing of the same bore and of sufficient length to make the bends. If the equipment is at hand to join the tubing with the stopcock the total cost will be a little less than one dollar. The total charge would be about one dollar and a quarter if a glass worker is employed. 543
JOURNAL OF CHEMICAL EDUCATION
544
MARCH, 1931
The apparatus should be held in rigid position to decrease the possibility of breakage. For this purpose a lead strap may be cut to fit over the tap and about the bottle. (A piece of a large automobile inner tube might be used.) A clasp is fixed in the strap (not shown in figure) for ease in removing the siphon. A cork is bored out to fit the back of the tap and rounded a t the other end to fit the bottle. This makes i t possible to tighten the strap without interfering with the action of the tap. One of the holes in the rubber stopper in the bottle is fitted with an air inlet tube. To start the siphon a large-size pipet bulb (as in Figure 2) may be used. Practice will enable one to start the siphon without spilling any of the solution, by closing the tap just before the FIGURE 2 liquid reaches it. If the solution is to be kept in a very pure condition the air inlet tube may lead through a wash mixture. In the case of basic solutions which should be free from carbonates, a large . drying . . tube containing - soda lime may be attached. The apparatus may be used easily and conveniently by students without danger of spilling acid on clothing. A lead drip tray should be cou+Rubber 3 Tubing structed under the eight bottles to protect the floor from occasional drops. Reserve bottles should be kept on hand so that the apparatus may be changed to a new supply without bothersome delay to student and instructor.
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Distribution of Special Solutions The common method of dispensing special solutions involves the tipping of the reagent bottle. Solutions are easily spilled and frequently the amount of solution actually needed is greatly exceeded. In large classes a great amount of solution may be wasted. Much time is needed to tip the bottle and to remove and replace its stopper. To solve these difficulties the apparatus in Figure 2 is +Glass Bead suggested. A 2.5-liter bottle is fitted with a No. 5 two-holed rubber stopper. Common small-bore glass tubing is used for the soout and oioet bulb connection. The bulb has a capacity of about 150 cc., which is sufficient volume to force the solution from the bottom of the bottle. The amount
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of the solution drawn from the bottle may be easily controlled by regulating the pressure on the pipet bulb. No tipping is necessary, the chance of spilling is reduced and quantities are easily and quickly forced out. Since the bottles do not have to be moved by the students, a special rack may be constructed a t the most convenient place in the room. Strongly alkaline solutions would dissolve COz in the air which is drawn back through the solution to refill the bulb. Bulbs may be purchased for about thirty-five cents each. Distributing Indicators Laboratory manuals usually call for an exact number of drops of indicators. Unless special droppers are provided, students are apt to use more than is needed and results are obscured and materials are wasted. A few burets attached to the wall by rubber tubing, as in Figure 3, may be used quickly and conveniently to take exact numbers of drops. Instead of using Mohr clamps to regulate the flow, glass beads are used in rubber tubing of proper size. By pinching the rubber tubing a t the bead the liquid flows by and is automatically shut off when the hand is removed (a point to be considered with careless students). A large piece of filter paper may be tacked to the floor below the apparatus to absorb any which might be acadentally dropped. The outlit may be easily fastened to a window or door casing as the convenience of position may require.
