Test tube semimicro

Solubility in 5 per cent, sodium hydroxide solution. Note whether there is any rise in temperature. If the compound appears insoluble, remove some of the supernatant liquid by means of a dropper to a semimicro test-tube (75 X 10 mm.), add 5 per cent, hydrochloric acid dropwise until acid, and note whether any precipitate (or turbidity) is formed. The production of the latter will place the compound in Group III. 

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 boihng hquids. 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. 

Acetyl chloride test (for primary and secondary amines). In a semimicro test-tube (75 X 10 mm.) treat 0-5 ml. (or 0-5 g.) of the compound with acetyl chloride drop by drop. Note whether reaction occurs. If no solid separates, pour the contents of the tube into 3 ml. of water and neutralise the aqueous layer with solid sodium bicarbonate. Observe whether a product different from the original compound is produced. 

The scale of the recrystallisation envisaged in group (1) means that the operations are carried out in the conventional manner but in apparatus of reduced size. Thus small conical flasks (5 to 20 ml), pear-shaped flasks (5 to 20 ml), semimicro test tubes (75 x 10mm or 100 x 12mm) or centrifuge tubes (1 to 5ml)... 

Place 0.1 g of the substance in a semimicro test tube (75 x 10 mm or 100 x l2mm) and proceed systematically with the various solvents as detailed on... 

Most semimicro centrifuges will accommodate both semimicro test-tubes (75 x 10 mm) and centrifuge tubes (up to 5 ml capacity). The advantages of the latter include easier removal of the mother liquor with a dropper, and, with small quantities of solids, the precipitate is more clearly visible (and the relative quantity is therefore more easily estimated) in a centrifuge tube (Fig. 11.17). 

Transferring of precipitates In some cases precipitates can be transferred from semimicro test-tubes with a small spatula (two convenient types in nickel or monel metal are shown in Fig. 11.20). This operation is usually difficult,... 

A small wooden clothes-peg (spring type) may also be used for holding semimicro test-tubes. 

Identification of gases Many anions (e.g. carbonate, sulphide, sulphite, thiosulphate, and hypochlorite) are usually identified by the volatile decomposition products obtained with the appropriate reagents. Suitable apparatuses for this purpose are shown in Fig. 11.30. The simplest form (a) consists of a semimicro test-tube with the accompanying filter tube a strip of test paper (or of filter paper moistened with the necessary reagent) about 3-4 mm wide is suspended in the filter tube . In those cases where spray is likely to affect the test paper, a loose plug of cotton wool should be placed at the narrow end of the filter tube . Apparatus b is employed when the test reagent is a liquid. A... 

Semimicro test-tubes (100 x 12-5 mm, 8 ml) and the appropriate filter tubes (80 x 9 mm) are marketed, and these may find application in analysis. The smaller 4 ml test-tubes will generally suffice their great advantage is that they can be used directly in a semimicro centrifuge in the buckets provided for the 3 ml centrifuge tubes. 

Spot test To 1 drop of the test solution add 1 drop nitric acid (2m), then 1 drop of the reagent. A red-violet precipitate or stain is formed if silver ions are present. Alternatively, the test may be performed on a spot plate, or in a semimicro test tube in the latter case the excess of the reagent is extracted with diethyl ether or amyl alcohol, when violet specks of the silver complex will be visible under the yellow solvent layer. 

Alternatively, place 1 ml test solution in a semimicro test-tube, add 0 5—1 ml reagent, and heat for a short time. The reagent is reduced to a blue compound, which can be extracted with amyl alcohol. 

Place a drop of the test solution in a semimicro test-tube, add a drop of the reagent, a drop of dilute nitric acid (1 1), and dilute to about 2 ml. Chromates give a red colouration this is best observed with a white light behind the tube. The reagent consists of a saturated solution of chromotropic acid in water. Concentration limit 1 in 5,000. 

Place 2 ml test solution, which has been rendered just alkaline with 2m sodium hydroxide, in a semimicro test-tube and add 1 drop of the reagent. A red colouration is obtained. 

The reaction may also be conducted in a semimicro test-tube here 0-3-0-5 ml amyl alcohol is added. The violet precipitate collects at the interface. 

An alternative technique is to warm (water bath) the test solution in a semimicro test-tube with a little dilute hydrochloric acid, and expose the evolved gas to filter paper upon which a stain of nickel(II) hydroxide has been made. The stain acquires a black colour. 

Thiosulphates and thiocyanates act similarly and must therefore be absent. The sulphide can, however, be separated by precipitation with zinc or cadmium carbonate. The precipitated sulphide may then be introduced, say, at the end of a platinum wire into a semimicro test-tube or centrifuge tube containing the iodine-azide reagent, when the evolution of nitrogen will be seen. 

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. 

Alternatively, mix 2 drops each of the alizarin-S and zirconyl chloride solutions in a semimicro test-tube, add a drop of dilute hydrochloric acid or of 1 1 (v/v) acetic acid, followed by 2 drops of the test solution. The pink colour will change to yellow. 

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