Boiling tube, semimicro

Evaporations Where rapid concentration of a liquid is required or where volatile gases must be expelled rapidly, the semimicro boiling tube (c in Fig. 

Test for nitrate (andI or nitrite) If ammonium is found, transfer the solution from test 5 with the aid of 0-5 ml water to a semimicro boiling tube (or crucible), add 0 5 ml sodium hydroxide solution and evaporate down to a volume of about 0-2 ml - this treatment completely decomposes the ammonium salt. Transfer the residue to a semimicro test-tube, rinse the vessel with 0-5 ml sodium hydroxide solution and add this to the contents of the test-tube. Then add 10 mg of Devarda s alloy (or of aluminium powder or thin foil), introduce a Pyrex filter tube provided with a loose plug of cotton wool at the lower end and containing a strip of red litmus paper or mercury(I) nitrate paper (Fig. II.29a), and place the assembly in the hot water rack. If frothing occurs, remove the apparatus from the water bath until the vigorous reaction has subsided. 

Tests with calcium chloride solution For tests 5 and 6 the soda extract has to be neutralized. To do this, take 0-5 ml of the soda extract in a semimicro boiling tube (or small crucible) and render it faintly acid with dilute nitric acid (use litmus paper). Heat to boiling for about 30 seconds to expel carbon dioxide, etc., allow to cool, then add dilute ammonia solution until just alkaline, and boil for 30 seconds to expel the slight excess of ammonia. 

Reddish-brown colouration, yielding a brown precipitate on dilution and boiling in a semimicro boiling tube, indicates acetate. 

Chloride in the presence of bromide and iodide Dissolve 10-20 mg of the solid in 0-5—1 ml water in a semimicro boiling tube (or use 5-10 drops of the soda extract acidified with dilute HN03), add 1-1 -5 ml concentrated HN03, and boil gently until the bromine and iodine are volatilized. Dilute with 1 ml water, and test for chloride by the addition of a few drops of AgN03 solution. 

Transfer to a semimicro boiling tube (or crucible or beaker) and boil off H2S (test with lead acetate paper). Add 3 drops of concentrated HN03 and boil to oxidise any iron(ll) to iron(lll) (8). The volume at this stage should be about 1 ml. Transfer to a semimicro test-tube or centrifuge tube. Add 50-100 mg of solid NH4C1 (or 0-25-0-50 ml of 20% NH4C1 solution), heat on a water bath, add concentrated NH3 solution until alkaline and then 2 drops in excess. Place the tube in the hot water rack for 2-3 minutes, stir and centrifuge. Wash (9). 

If the centrifugate is brown or dark-coloured, Ni may be suspected. The dark-coloured solution contains colloidal NiS, which centrifuges with difficulty. It may be acidified with dilute acetic acid and boiled (crucible or semimicro boiling tube) until the NiS has coagulated this may be added to the Group IIIB precipitate or tested separately for Ni. 

Add 10-15 drops dilute HC1 and 5 drops of M NaOCl solution, stir and place in a hot water bath for 1-2 minutes. Transfer the liquid with the aid of 1 ml water to a semimicro boiling tube and boil gently to expel Cl2. Divide the solution into 2 parts. 

Transfer to a semimicro boiling tube, boil to expel H2S (test with lead acetate paper), return liquid to semimicro centrifuge tube, cool, add excess NaOH solution (0-5-1 ml) and 4 drops of 3 per cent H202 solution heat on a water bath for 3 minutes. Centrifuge. 

Alternatively, dissolve the ppt. in 0-5 ml dilute HN03 with the addition of 1-2 drops of 3 per cent H202 solution. Transfer to a semimicro boiling tube with the aid of 0-5 ml water, and boil to decompose excess H202. Cool, add 0-5 ml concentrated HNOa and 250 mg Pb02. Boil for 1 minute and allow to stand. 

May contain Ca2+. Transfer most of the liquid to a semimicro boiling tube or a small crucible, and evaporate almost to dryness (FUME CUPBOARD). Transfer to a centrifuge tube with the aid of 0-5-1 ml water, render alkaline with NH3 solution, and add excess (NH4)2(COO)2 solution (3). Allow to stand in a hot water bath for 2-3 minutes. 

Evaporations where rapid concentration of a liquid is required or where volatile gases must be expelled rapidly, the semimicro boiling tube (c in Fig. 2.11) may be employed. Useful holders, constructed of a light metal alloy, are shown in Fig. 2.25 b is to be preferred as the boiling tube cannot fall out by mere pressure on the holder at the point where it is usually held. Slow evaporation may be achieved by heating in a test-tube, crucible, or beaker on a water bath. 

A Pyrex micro filter (Fig. XII, 2, 18) of 8 ml. capacity and furnished with a sintered glass disc is useful for the filtration of hot or boiling liquids. The long cylindrical tube reduces evaporation. The filter may be inserted into a test-tube with side arm (Fig. XII, 2, 13) and the filtrate collected in a centrifuge tube or semimicro test-tube receiver. 

Place a few drops of the test solution in a semimicro test-tube, acidify with dilute hydrochloric acid, add a small fragment of broken porcelain and attach a gas absorption pipette (Fig. II.29c) charged with a drop or two of ammonia solution. Boil the solution in the test-tube gently so as to distil any HSCN present into the ammonia solution. Rinse the ammonia solution into a clean semimicro test-tube, acidify slightly with dilute hydrochloric acid and add a drop of iron(III) chloride solution. A red colouration is obtained. 

A more elaborate arrangement which will, however, meet the requirements of several workers, is Barber s water bath rack (Fig. 2.23). The dimensions of a rack of smaller size are given in Fig. 2.24, This rack will accommodate four centrifuge tubes and four semimicro test-tubes. The apparatus is constructed of monel metal, stainless steel, a plastic material which is unaffected by water at 100°C, or of brass which is subsequently tinned. The brass may be tinned by boiling with 20% sodium hydroxide solution containing a few lumps of metallic tin. 

Table VI.12 Separation of Group I cations on the semimicro scale The residue may contain PbCl2, AgCl, and Hg2Cl2. Add 1 ml hot water to the ppt., place the tube in a boiling water bath for 1-2 minutes, and stir continuously. Centrifuge rapidly separate the solution from the residue with a capillary pipette and transfer the clear solution to a centrifuge tube.

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