1 Small retort, best tubulated with stopper, about 4 to 6 oz. capacity. DIVISION II. 6 Test-tubes, 5 or 6 inches long and from to inch in diameter. 1 Test-tube cleaner. 2 Lengths of hard glass tubing, rather more than 1th inch internal diameter. 1 Thistle funnel. [1 Clock glass, about 4 inches across.] 2 Round ground-glass plates, 3 inches across. 2 Porcelain dishes, one 2 inches across, one 3 inches across. 3 Watch glasses, about 2 inches across. 2 Small flasks, about 4 oz. capacity. .* Red or black india-rubber tubing ;* 1 piece 18 inches long 5 and inch internal diameter, 1 piece 6 inches long 16 1 Bunsen-burner* with separate rose-top. 1 Small pestle and mortar. 1 Iron tripod stand. 1 Piece of wire gauze, 5 inches square. 1 Round file. 1 Triangular file. 1 Small set of cork-borers. 1 Small retort-stand, 12 inches in height, and fitted with 3 brass rings. DIVISION III. 4 Glass funnels, two 2 inches across at the top, two 21 inches across at the top. 2 Tobacco-pipe cleaners, for cleaning glass tubes. * The Bunsen-burner and gas-tubing may be fixtures on each working bench, and will not then be required for each student. 2 Boiling tubes, 6 or 7 inches long, from 1 to 1 inch across. 1 Test-tube stand with at least 12 holes. 1 Nest of 3 or 4 small-sized beakers. 1 Length of glass rod. 1 Small porcelain crucible about 1 inch across, and lid. 1 Strip of platinum-foil, 2 inches by 1 inch. 2 Pieces of platinum-wire,* each 1 to 2 inches long. 1 Black's blowpipe. 1 Pipeclay triangle, 2 inches in the side. 1 Pair of brass crucible tongs. 1 Large flask for wash-bottle, 18 oz. capacity and from 1 to 1 inch across the neck. 1 Wooden filtering-stand. 1 Tin filter-dryer. 1 Small wicker-basket for draining test-tubes and other glass and porcelain apparatus after they have been washed. Little toilet-baskets, 12 inches in length by 5 and 4 inches high, serve well. : Note. For the experiments with gases the student will also require : A small piece of candle. A wax taper, or slips of wood. A few sound corks of such a size as to fit test-tubes or small flasks. Caution. In a laboratory where many students are working, it is best to mark at once each piece of apparatus with initials, number, or with some private mark, so as to be able to recognise it if mislaid. Glass, metal, or porcelain apparatus may be notched with the edge of the three-cornered file, or characters may be scratched upon it with the sharp points made by breaking off the tip of a three-cornered file. Wooden. apparatus can be written upon with pen and ink, or scratched with the tip of a penknife. * Platinum-wire containing Ba is not uncommon in commerce: it is known by giving a persistent green colour to the Bunsen flame, and is useless for analytical purposes. T APPARATUS FOR GENERAL USE. 495. The following apparatus need not be purchased by each student, but should be kept in constant readiness for general use: 496. An Indigo-prism.-A hollow glass-prism having an extremely small angle at its extremity, with ground-glass stopper fitting water-tight into the neck, is purchased; this is to be very nearly filled with solution of indigo, and the stopper then tied in securely with fine copper wire. The indigo solution is made by diluting a solution of indigo in strong sulphuric acid, with water in a thin glass beaker or a porcelain dish until it has the required intensity of colour;* the liquid is then allowed to stand for several days to give time for a sediment to form and settle completely, and when quite clear is decanted into the prism, In the thicker part of the prism the blue must be so intense as to arrest the passage of the light from a flame coloured yellow with a sodium compound, and to cause the potassium flame coloration to appear red. 497. Several small slips of cobalt-glass.-This glass is used for the same purpose as the indigo-prism, but the prism is to be preferred more especially for the examination for Sr. 498. Set of cork-borers.-These are used for perforating a cork into which a piece of glass tubing has to be inserted. Nests of borers containing three or four small sizes will be sufficient. 499. Sulphuretted-hydrogen apparatus. It is highly advisable to employ a large apparatus which will supply the gas to all who are working in the laboratory. The use of a small private apparatus by each student, not only causes unnecessary waste of materials and time, but vitiates the air of the laboratory whilst it is being washed out. Many forms of apparatus have been devised to supply the gas in a constant stream; probably the following, the sim * The addition of the indigo solution to 10 times its measure of water will usually give the required shade. plicity, efficiency, and cheapness of which render it very satisfactory, will be found the most generally useful. Note.-The level of the liquids in the vessels is shown by dotted lines; the vessel A when lowered from its stand is also shown in dotted outline. The whole is drawn in section. 500. Sulphuretted-hydrogen apparatus.-Two large bottles, A and B, with wide necks and tubulures near the bottom, and of at least two quarts capacity, are fitted as shown in section in figure 39.* India-rubber stoppers should be used instead of corks, as the latter soon become sodden with acid and rotten, and also lose their elasticity and permit leakage. Into B (after laying it upon its side to prevent breaking the bottom) is placed a quantity of small pebbles or broken glass, sufficient to form a layer about half an inch deep; upon this is dropped the ferrous sulphide in lumps: the cork is then inserted, the clamp at E being closed. The glass tube fixed in the lower tubulure of B should be bent downwards, so that its end nearly touches the bottom of the vessel. This *This apparatus may be purchased completely fitted from Messrs Mottershead of Manchester and from most apparatus sellers. . drains the acid out of B to the lowest possible level when A is lowered. Strong commercial hydrochloric acid* is poured into A, then an equal bulk of water is added, and the liquids are well mixed by shaking the vessel. When the gas is required, the vessel A is raised by being placed on a stand of suitable height, the acid runs into B, generates the gas by acting on the ferrous sulphide, and by the pressure of the liquid in A this gas is forced through a little water in the washing-bottle C, and thence through a bent tube at D into the liquid which is to be saturated with sulphuretted hydrogen. When the flow of the gas is to be stopped a small screwclamp on the india-rubber joint at E is tightened: by proper management of this screw-clamp the stream of gas can be either totally arrested or controlled to any required extent: this clamp must always be so regulated as to permit of as little waste of gas as possible whilst using the apparatus. During working hours the vessel A should be kept raised, as shown in the figure; when laboratory work ceases it should be lowered to the position shown in dotted outline. The vessel B is always kept slightly raised by being placed on a wooden block or some bricks, so as to encourage the flow of the last portions of acid out of it into A when A is lowered. When the acid is spent, it is easily poured out of A and replaced by fresh: lumps of ferrous sulphide are added as required through the neck of B. The removal of the spent acid and the cleansing of the apparatus should be performed in the open air, or at a sink in a cupboard provided with a good draught. The neck of A should be kept stopped with a cork carrying a bent funnel whose bend is filled with oil or glycerine; this lessens the escape of gas dissolved in the acid, and tends to prevent the apparatus from causing a smell. If several students require to use the gas at the same time, the broad * H2SO4 does not answer for this purpose as well as HCl, since FeSO is apt to crystallise in the apparatus, impeding or preventing the action of the acid and its flow through the connecting tube. |