SIMPLE TIME-SAVERS in the PREPARATION of SOLUTIONS L. A. MUNRO Queens University, Kingston, Canada
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CONSIDERABLE saving of time can be achieved by the use of home-made dissolving funnels for the preparation of solutions. The principle is simple. A perforated container filled with solute is suspended in the upper portion of the solvent. The solution formed in the funnel is denser than the solvent so it streams to the bottom, fresh solvent taking its place. This gives very efficient stirring by gravity. The reader may be familiar with "dissolvers" of the funnel type. Three simple types are described below. These can easily be made by the amateur glass blower from apparatus a t hand. Type A is made from an old 100200 cc. pipet. Thinwalled bulbs a r e blown as shown in the diagram. The thin walls are broken by tapping with a 0 0 0 ,, file, when the required number of b u l b s has b e e n blown. The edges of the holes are fireA B polished in the tip of a small flame. One end of the pipet is then cut off near the shoulder by means of a hot wire and the pierced part is flanged. The small tube is cut off near the base and a plug of glass wool is inserted, the shoulder being heated until the edges of the plug fuse to the walls. The completed dissolving tube is suspended by a nicrome triangle. In an experiment using sticks of NaOH, 15 g. was weighed into A, and suspended in a tall beaker containing 85 cc. of water. The whole dissolved in 6.0 minutes. In a second experiment the same quantity
was added to the same volume in a beaker and the mixture was stirred continuously with a stirring rod. This required six minutes three seconds for complete solution. I t seems therefore that the "gravity stirring" induced by the dissolving tube A is as effective as constant stirring with a stirring rod. For larger quantities a dissolver of type B or C is recommended. Of these, type B is more easily constructed. I t is made from a large neck, round bottom Pyrex flask, using a fine-pointed oxygen flame. This type was used for making up NaOH for a large class in qualitative analysis. -- - - - - - - - - - - - % weighed N & H was placed in B, suspended bythe neckin a large beaker. Solution was quite rapid. Theresultingsolution was then diluted to therequiredstrength. Type C is a little 0 0 0 more difficult to make but gives a convenient shape. Holes are first blown C as before. Indentations are made in the neck of the Erlenmeyer. The base is then cut off by means of a hot wire and a stream of water from a wash bottle. A plug of glass wool is inserted on top of the indentations and the funnel is suspended by a ring. One should be sure that the walls of the little bulbs are thin enough to be shattered by tapping with a file. Should the projecting bulb "blow out," the edges should be fire polished and a plug of asbestos or cotton wool inserted when cool. Some prefer to make all the holes in this w v, plugging each until the work is completed.
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