Suction ball

A good supply of capillary tubes, suction balls (see page 1113), and capillary pipettes of various sizes should also be prepared in advance in considerable numbers. 

Liquids are measured out for a reaction by means of capillaries fitted with a rubber cap, a suction ball, a dropping tube, or a pipette. 

It sometimes happens that recovery of very small amounts of a substance by evaporation of a dilute solution in a relatively large flask yields the material as a thin film on the wall of the vessel in such cases quantitative recovery of the substance can be achieved by means of a suction ball. 

This suction ball is a plum-shaped 0.5-20 mm glass ball with capillaries of medium internal diameter (length 100-350 mm, diameter 0.3-2.5 mm) attached at diametrically opposite sides.62 The principle of operating a suction ball is to seal one capillary, warm the ball so that air or solvent vapor is driven out of the other end, and then to dip the open end into the liquid which is then sucked into the ball as the latter cools. The suction ball can be emptied either analogously by warming or by cutting off the sealed end of the capillary. The suction ball has many advantages over the micropipette with rubber cap used for similar purposes. 

Figure 10. Preparation of a suction ball. For a description of the steps a-f see the text.

It is also possible to repeat several times the evaporation and condensation of the solvent added to the larger vessel, before introducing this solution into the suction ball in this way the lower part of the vessel is washed by the condensed solvent that runs down the walls. 

If the solution is to be preserved in the suction ball, all the fractions are introduced into one ball, which is then turned so that the open capillary is on top the solution in this capillary is allowed to run back completely into the ball, the ball is then warmed and quickly reversed and the open capillary is dipped in pure solvent, which washes the capillary as it is sucked up these operations are then repeated for a second and a third washing. It is inadvisable to carry out this repeated suction into the ball with solvents boiling below 50-60°. When all the materials are in the ball the two capillaries, one after the other, are shortened and sealed. 

The vessel and suction ball must be firmly clamped (see Figure 11) until filtration is complete. If necessary, the wall of the vessel may be washed down with a little solvent from a micropipette, even before filtration is complete. 

After the filtration, the filter end is cut off and, after being emptied, the suction ball is washed with solvent in the usual way. When dilution of the solution must be avoided, some of the solvent may be evaporated by heat, provided, of course, that further heating does not decompose the solute the-solvent vapor above the solution is sucked up into the empty suction ball, where it condenses and washes the walls of the ball this condensate is then removed from the ball in the usual way two or three repetitions of this process provide quantitative filtration. 

The classical use of a micro filter funnel and folded paper or cotton wool always leads to loss of material and when a suction ball is used, the filtrate contains neither threads from the paper nor colloidal portions of the clarifying agent. If the solute crystallizes in the suction ball during or after filtration, then, when filtration is complete and the filter end has been cut off, the suction ball is heated in a bath with the open capillary upwards until the crystals have redissolved. 

Various methods have been described in the literature72,78,79 for recrystallization of very small amounts of material on a microscope carrier glass or in a capillary tube the former method is suitable only for orienting experiments, and the latter is rather wearisome. In our experience it is, however, possible to recrystallize even very small amounts of material very nicely by means of testtubes of suitable size and a suction ball. 

When recrystallization is effected in testtubes or pear-shaped flasks, the method used to separate the mother liquor must be adapted to the nature of the crystals produced. For well developed crystals a suction ball is used whose capillary end is drawn out to a fine capillary if the end of the capillary becomes blocked with crystals during the filtration, these can be removed by cautiously rotating the ball — but no air must be allowed to penetrate into the ball when the supernatant mother liquor has been sucked up, the crystals are washed with a few drops of solvent, which is again removed by means of the suction ball. 

When strong cooling and a low-boiling solvent are used, it is advisable to use a double suction ball, as illustrated in Figure lOe, one ball being warmed and the other used for sucking up the mother liquor. 

Substances that separate in a very finely divided state and cannot be filtered by the methods described above must be centrifuged. The liquid lying above the sediment can then be removed by a suction ball, after which the precipitate should be stirred with fresh solvent and again centrifuged. The paste resulting from these operations is freed from residual solvent on a porous plate or in the centrifuge vessel itself. 

Various types of collar flask permit distillation of any amount of liquid between 50 mg and 5 g. For 50-1000 mg quantities the flask (Figures 22a and 22 b) is filled with thin-fibre glass wool, preferably by use of a glass tube that is thin enough to pass through the narrow neck of the flask, and the substance to be distilled is placed on the glass wool by means of a suction ball. Any solvent present is removed at room temperature by application of a slight vacuum, then the apparatus is immersed up to the vacuum tube in a water-bath and is warmed later it is immersed to half-way up the neck in a paraffin... 

Extraction of solid substances. For substances that are readily extracted it often suffices merely to digest or boil them with an appropriate amount of a suitable solvent. The solvent is then removed by centrifugation or by means of a suction ball adapted for filtration. Specialized apparatus103-107 is preferably used for substances that are difficult to extract or sparingly soluble. 

Small amounts of solution are dried in small testtubes fitted with stoppers, and the drying agent is removed by transferring the solution to a suction ball fitted with a cotton wool filter. 

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