Dropping pipette

The transference of a liquid from one vessel to another is best carried out by means of a dropping pipette A (Fig. 30). For measuring out a definite volume of liquid it is obviously an advantage to have a calibrated pipette B (Fig. 30) of i or 5 ml. total capacity. Alternatively, semi-micro burettes reading to 0 02 ml. are particularly convenient for class work. 

When the correct solvent for recrystallisation is not known a procedure similar to that given on pp. 15-16 should be followed, but on the semi-micro scale not more than 10 mg. of the solid should be placed in the tapered-end test-tube (Fig. 29(B)) and about o i ml. of the solvent should be added from the calibrated dropping-pipette (Fig. 30(B)). If the compound dissolves readily in the cold, the solvent is unsuitable, but the solution should not be discarded. [In this case recourse should be had to the use of mixed solvents (p. 18). For example if the substance is very soluble in ethanol, water should be added from a calibrated pipette with shaking to determine whether crystallisation will now take place, indicated by a cloudiness or by the separation of solid.]... 

Procedure. The water sample should be collected by carefully filling a 200-250 mL bottle to the very top and stoppering it while it is below the water surface. This should eliminate any further dissolution of atmospheric oxygen. By using a dropping pipette placed below the surface of the water sample, add 1 mL of a 50 per cent manganese(II) solution (Note 1) and in a similar way add 1 mL of alkaline iodide-azide solution (Note 2). Re-stopper the water sample and shake the mixture well. The manganese(III) hydroxide forms as a brown precipitate. Allow the precipitate to settle completely for 15 minutes and add 2 mL of concentrated phosphoric(V) acid (85 per cent). Replace the stopper and turn the bottle upside-down two or three times in order to mix the contents. The brown precipitate will dissolve and release iodine in the solution (Note 3). 

Using a clean dropping pipette, decant some of the stock INP solution. 

Using a dropping pipette, add LOOM sodium hydroxide (NaOH) drop by drop to the acid solution, stirring after each drop, until 1 drop of base causes the solution to remain a permanent red color. 

Materials glacial acetic acid distilled water 10-mL graduated cylinder dropping pipette 50-mL beaker 24-well microplate conductivity tester with battery stirring rod... 

Use a 10-mL graduated cylinder to measure 3 mL of glacial acetic acid. Use a dropping pipette to transfer the 3 mL of glacial acetic acid into well A1 of a 24-well microplate. 

It should be emphasised that in all these operations the laboratory worker should have readily to hand racks, retort stands, clamps and bosses to hold and support the centrifuge tubes and dropping pipettes, and watch glasses to cover tube ends and prevent the entry of dust. 

Procedure for Lassaigne s test. Support a Pyrex test tube (150 x 12 mm) vertically in a clamp lined with sheet cork. Place a cube (c. 4 mm = 0.04 g) of freshly cut sodium in the tube (for precautions in the use of sodium see Section 4.2.68, p. 462). Have in readiness about 0.05 g of the compound (if a solid) on a microspatula or tip of a knife blade, or about 3 drops of the compound (if a liquid) in a dropping pipette. Heat the tube steadily until sodium vapour, which is dark grey in colour, rises 2-3 cm in the test tube and drop the sample, preferably portion-wise, directly on to the molten sodium (CAUTION there may be a slight explosion). Do not allow the sample to fall on to the side of the tube above the vapour layer. Heat the tube to redness for about 2 minutes, and then allow it to cool. Add about 3 ml of methanol to decompose any unreacted sodium and then halffill the tube with distilled water. Boil gently for a few minutes to remove the methanol and extract inorganic salts from the fusion residue gently crush the... 

Cone. HNO3 and dropping pipette Used to acidify water samples in field base... 

The measurement of the amount put on is probably best made by means of an Agla micrometer syringe 1 this measures down to one ten-thousandth of a c.c. A simple dropping pipette with a teat and a fine tip is somewhat more convenient, and accurate to about 2 per cent. with this a slight correction needs to be made for the evaporation of the more volatile solvents.2... 

Stand with double boss, overhead projector, 200-mL Erlenmeyer flask, 250-mL measuring cylinder, balance, spatula, dropping pipette, safety glasses, protec live gloves. 

Monar and pestle, spatula, two dropping pipettes, two evaporating dishes, safety glasses, protective gloves. 

The chemicals are weighed out, transferred to a large sheet of paper and mixed cautiously by moving the paper to and fro. Tliey are poured on to the fire-resistant to form an elongated heap. The mixtures arc ignited at one edge with 1-2 drops of concentrated sulfuric acid added from a dropping pipette a sparkler can also be used. 

Two. SOO-ml. beakers, four 250-mL graduated beakers, dropping pipettes, stock bottles for indicator solutions, two 1-L measuring cyclinders, safety glasses, proiective gloves. 

The seven test tubes are filled half full with a solution of 1 g of one of the hydroxybenzenes in 20 mL of a 1 1 mixture of water and ethanol. A small amount of a 5 % aqueous FeCh solution is added to each test tube using a dropping pipette. The test tubes are shaken for a short time and the white cardboard placed behind them. The colors formed in the reactions are as follows ... 

Eight large test tubes with stand, dropping pipettes, glass rods, protective gloves, safety glass. 

Full bottle of mineral water (no natural or artificial colorings ) with screw top, dropping pipette, 0.1 % alcoholic solution of bromocresol green, safety glasses. 

Slide projector, screen, measuring cylinder, large flat-bottomed flask (l-L or 2-L), beakers, glass rods, dropping pipettes, room which can be darkened, safety glasses, protective gloves. 

The dilute hydrochloric acid is now added slowly from a dropping pipette with continuous careful stirring. A slight light scattering effect is observed from... 

Two Petri dishes, insulated copper wire, banana plugs, alligator clips, glass plate, polished nickel-plated sheet iron (about 10 x 15 cm) as support, source of DC current (lOV), hair dryer, spatula, measuring cylinder, dropping pipettes, safety glasses, protective gloves. 

Narrow-necked polythene bottles (50 or 100-mL), piezoelectric spark generator, sparking plug attached to base plate, gas inlet tubes, 1-L beaker, dropping pipette, measuring cylinder, safety glasses, protective gloves. 

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