Magnetic flea

The sample solution was stirred briefly with a magnetic flea . 

Stir the liquid or solution with a magnetic flea (see p. 35) which should be removed before further processing of the chemicals. 

These consist of a flat metal or ceramic plate, which is heated electrically, and varies in size for use by an individual or by several people at the same time. The small versions normally have a built-in magnetic stirrer, which can be used to stir the liquid with a magnetic flea . 

These are mostly used to heat round-bottom flasks at temperatures above 100°C. The oil bath, containing the heating fluid, is usually a non-ferrous metal or Pyrex dish and heated on a stirrer hot plate, and the temperature of the bath is measured with a thermometer. The oil bath should never be more than half-full, to allow a margin of safety for thermal expansion of the oil, and stirred with a magnetic flea to ensure even heating. The equipment used in a typical oil bath is shown in Fig. 5.12b. 

Some mantles, stirrer mantles , have a built-in magnetic stirrer just like a stirrer hot plate and can be used to mix the liquid using a magnetic flea or bar (Fig. 5.13b). Stirrer mantles have two controls on the side make sure that you know the function of each, since one controls the extent of heating and the other the stirrer speed. 

When using an internal thermometer to measure the temperature of a liquid or solution which is being stirred with a magnetic flea or stirring bar, ensure that the thermometer bulb does not come into contact with it. 

This is a modification of gravity filtration (p. 28), designed to remove solvent-insoluble impurities, charcoal, anti-bumping granules or magnetic fleas from the hot solution before cooling the solution to form the crystals of purified product. 

Add the liquid to be distilled to the distillation flask using a stemmed funnel, together with antibumping granules or boiling stick or a magnetic flea . The flask should not be more than 50% full. Reclamp the flask in position. 

Round-bottom or pear-shaped reaction flasks are preferred, but note that stirring with the usual type of magnetic flea is not possible in pear-shaped flasks. The flasks can have multiple necks so that the apparatus can be configured for temperature measurement, addition of solids or liquids, mechanical stirring and inert atmosphere work (p. 125). No matter which arrangement of components is used, always clamp the reaction flask at the neck and keep the heaviest components (such as an addition funnel containing another chemical) vertically above the flask. A condenser will still function at 30° from vertical and it is not very heavy. 

Insert magnetic flea in receptor chamber and mount epidermal membranes stratum corneum side up in horizontal Franz-type diffusion cells, that are then placed on a magnetic stirrer plate in a water bath (Fig. 1) (see Note 8). 

Fill the flask to about one-third of its volume with solvent, add some anti-bumping granules (or a magnetic flea , if a stirrer-mantle is being used) and clamp it into position in the mantle. 

When the extraction is complete, allow the apparatus to cool and dismantle it. Place the extraction thimble in the fume cupboard to allow the solvent to evaporate and the dispose of it appropriately. Gravity filter or decant the solvent in the reservoir flask to remove the anti-bumping granules of magnetic flea" and remove the solvent by distillation (p. 107) or rotary evaporation (p. 122). 

In a round-bottom flask (100 mL) place 2,4-dimethyl-benzoic acid (3.0 g, 0.02 moll, anhydrous potassium carbonate (3.3 g, 0.024 mol) and a small magnetic flea. In the fume cupboard and wearing protective gloves, carefully weigh out dimethyfsulphate (2.8 g. 0.022 mol)... 

Fluorescence DNA binding titrations are performed in the reverse mode by adding 5.0 jjlI aliquots of a 1.0 mM DNA stock to 3.0 ml of 5 pM protein in a 4 ml fluorescence quartz cell (Fig. 6). A carefully calibrated Unimetrics syringe with a utility stop permits reproducible, repetitive deliveries of a constant volume. The solution is mixed by constant stirring using a magnetic flea at the bottom of the cell. Nucleic acid and protein stock concentrations are determined by UV... 

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