Water-Bath

If the hydrogencarbonate is in solution and the cation is Ca or Mg. the insoluble carbonate is precipitated this reaction may be used, therefore, to remove hardness in water by precipitation of Ca or Mg ions.) The ease of decomposition of hydrogencar-bonates affords a test to distinguish between a hydrogencarbonate and a carbonate carbon dioxide is evolved by a hydrogencarbonate, but not by a carbonate, if it is heated, either as the solid or in solution, on a boiling water bath. 

Phosphorus(lll) oxide is prepared by passing a slow (i.e. limited) stream of air over burning white phosphorus. A mixture of the two oxides P40(, and P40,o is thereby formed the (V) oxide can be condensed out of the emerging gas stream as a solid by passing through a U tube heated in a water bath to about 330 K the more volatile (III) oxide passes on and can be condensed in a second U trap surrounded by ice. 

About 0.5 g of iodine is placed in a small flask fitted with a long reflux air condenser and 15 cm of fuming nitric acid (b.p. 380 K) are added. The mixture is then heated on a water bath at 385-390 K in a fume cupboard until the reaction seems to be complete. This takes about an hour. The solution is then transferred to an evaporating basin and evaporated to dryness on a steam bath. The iodic acid... 

Most students will be familiar with simple distillation from their practical inorganic chemistry. Other students should determine the boiling-point of acetone (56°), using a water-bath and water-condenser, or of benzene (81 ), using a sand-bath and water-condenser, and finally of either aniline (184 ) or nitrobenzene (210 ), using for both these liquids a sand-bath and air-condenser. 

The crude material is therefore placed either in a round-bottomed bolt-head flask (Fig. 8) or in a conical flask, the solvent added (again in slight deficiency) and a reflux water-condenser fitted to the flask as shown. The mixture is boiled either on a water-bath or over a gauze, and then more solvent added cautiously down the condenser until a clear solution (apart from insoluble impurities) is again obtained. It is then filtered hot as described above. 

Concentrate each of the two solutions (or eluates) to about 20 ml, by distilling off the greater part of the benzene, the distilling-flask being immersed in the boiling water-bath. Then pour the concentrated solution into an evaporating-basin, and evaporate the remaining benzene (preferably in a fume-cupboard) in the absence of free flames, i.e., on an electrically heated water-bath, or on a steam-bath directly connected to a steam-pipe. Wash the dry residue from the first eluate with petrol and then dry it in a desiccator pure o-nitroaniline, m.p. 72°, is obtained. Wash the second residue similarly with a small quantity of benzene and dry pure />--nitroaniline, m.p. 148" , is obtained. Record the yield and m.p. of each component. 

A skilled worker can use a micro-Bunsen burner for most types of heating. Nevertheless, as there is a tendency for a liquid to shoot out of a small test tube when heated, it is preferable to place the tube in a hot water-bath or in a metal heating block. A small glycerol bath is suitable for distillations and heating under reflux, the glycerol being subsequently easily removed from flasks, etc., by washing with water. 

The solution of potassium ethyl sulphate can be concentrated on the water-bath without appreciable hydrolysis, and the sulphate finally crystallised out-... 

Yield, about 6g. To obtain a second (but necessarily less pure) crop of the sulphate, evaporate the filtrate further on the water-bath, and cool as before. 

Now filter the ether through a fluted filter-paper directly into a 100 ml. distilling-flask, and then equip the latter with a 100° thermometer and a double-surface condenser to the end of the latter attach a receiver with a rubber delivery-tube precisely as before. Place the flask cautiously in a water-bath, the contents of which have previously been heated to about 60° at some distance from the apparatus arrange the depth of the flask in the water-bath so that the ether distils slowly over. Collect the fraction boiling between 34-39°. Yield, 25 g. (35 ml.). Not more than a verv small residue of etlianol should remain in the flask. 

Consequently traces of these unstable peroxides are present in samples of all the lower aliphatic ethers unless the samples have been freshly distilled. If these ethers when being distilled are heated on, for example, an electric heater, the final residue of peroxide may become sufficiently hot to explode violently. The use of a water-bath for heating, as described above, decreases considerably both the risk of the ether catching fire and of the peroxide exploding. 

Place 0 5 ml. of acetone, 20 ml. of 10% aqueous potassium iodide solution and 8 ml. of 10% aqueous sodium hydroxide solution in a 50 ml. conical flask, and then add 20 ml. of a freshly prepared molar solution of sodium hypochlorite. Well mix the contents of the flask, when the yellow iodoform will begin to separate almost immediately allow the mixture to stand at room temperature for 10 minutes, and then filter at the pump, wash with cold w ater, and drain thoroughly. Yield of Crude material, 1 4 g. Recrystallise the crude iodoform from methylated spirit. For this purpose, place the crude material in a 50 ml. round-bottomed flask fitted with a reflux water-condenser, add a small quantity of methylated spirit, and heat to boiling on a water-bath then add more methylated spirit cautiously down the condenser until all the iodoform has dissolved. Filter the hot solution through a fluted filter-paper directly into a small beaker or conical flask, and then cool in ice-water. The iodoform rapidly crystallises. Filter at the pump, drain thoroughly and dry. 

The oxime is freely soluble in water and in most organic liquids. Recrystallise the crude dry product from a minimum of 60-80 petrol or (less suitably) cyclohexane for this purpose first determine approximately, by means of a small-scale test-tube experiment, the minimum proportion of the hot solvent required to dissolve the oxime from about 0-5 g. of the crude material. Then place the bulk of the crude product in a small (100 ml.) round-bottomed or conical flask fitted with a reflux water-condenser, add the required amount of the solvent and boil the mixture on a water-bath. Then turn out the gas, and quickly filter the hot mixture through a fluted filter-paper into a conical flask the sodium chloride remains on the filter, whilst the filtrate on cooling in ice-water deposits the acetoxime as colourless crystals. These, when filtered anddried (either by pressing between drying-paper or by placing in an atmospheric desiccator) have m.p. 60 . Acetoxime sublimes rather readily when exposed to the air, and rapidly when warmed or when placed in a vacuum. Hence the necessity for an atmospheric desiccator for drying purposes. 

After about 20 minutes, when the liquid should be dry, filter it through a small fluted filter-paper into a 100 ml. distilling-flask attached to a water-condenser. Add some fragments of unglazed porcelain to the ethyl acetate, fit a 100° thermometer to the flask, and place the latter on a cold water-bath, which is then brought to the boil. Some ether is always formed as a by-product with the ethyl acetate, and by these means is carefully distilled off as a... 

Fit the flask with a 100° thermometer and a water-condenser, and distil the ethyl iodide carefully from a water-bath, collecting the fraction which distils between 68° and 73°. Yield, about 24 g. 

Dissolve 5 g. of aniline hydrochloride in 120 ml. of hot water contained in a 200 ml. conical flask and then add 4 g. of potassium cyanate. Heat the solution on a water-bath for 30 minutes, adding about 1-2 g. of animal charcoal towards the end of the heating if a slight turbidity has developed. Now bring the solution quickly to the boil over a gauze, and filter it at the pump, using a Buchner funnel and flask which have been preheated by the filtration of some boiling distilled water. The clear... 

Add in turn benzyl chloride (8 3 g., 8 o ml.) and powdered thiourea (5 gm.) to 10 ml. of 95% ethanol in a 100 ml. flask fitted with a reflux condenser. Warm the mixture on the water-bath with gentle shaking until the reaction occurs and the effervescence subsides then boil the mixture under reflux for 30 minutes. Cool the clear solution in ice-water, filter off the crystalline deposit of the benzylthiouronium chloride at the pump, wash it with ice-cold ethyl acetate, and dry in a desiccator. Yield, 11-12 g., m.p. 170-174°. The white product is sufficiently pure for use as a reagent. It is very soluble in cold water and ethanol, but can be recrystallised by adding ethanol dropwise to a boiling suspension in ethyl acetate or acetone until a clear solution is just obtained, and then rapidly cooling. 

Add 15 g, of chloroacetic acid to 300 ml. of aqueous ammonia solution d, o-88o) contained in a 750 ml. conical flask. (The manipulation of the concentrated ammonia should preferably be carried out in a fume-cupboard, and great care taken to avoid ammonia fumes.) Cork the flask loosely and set aside overnight at room temperature. Now concentrate the solution to about 30 ml. by distillation under reduced pressure. For this purpose, place the solution in a suitable distilling-flask with some fragments of unglazed porcelain, fit a capillary tube to the neck of the flask, and connect the flask through a water-condenser and receiver to a water-pump then heat the flask carefully on a water-bath. Make the concentrated solution up to 40 ml. by the addition of water, filter, and then add 250 ml. of methanol. Cool the solution in ice-water, stir well, and set aside for ca. I hour, when the precipitation of the glycine will be complete. 

In view of the small volume of nitromethane to be manipulated, the crude nitromethane may be extracted from the aqueous distillate with ether (30-40 ml.). Dry the ethereal extract over sodium sulphate, filter through a fluted filter-paper, and then distil off the ether on a water-bath with the usual precautions (Fig. 64, p. 163 Fig, 23(E), p. 45) finally distil the residual nitromethane. 

Carry out this preparation precisely as described for the a-compound, but instead of zinc chloride add 2 5 g. of anhydrous powdered sodium acetate (preparation, p. 116) to the acetic anhydride. When this mixture has been heated on the water-bath for 5 minutes, and the greater part of the acetate has dissolved, add the 5 g. of powdered glucose. After heating for I hour, pour into cold water as before. The viscous oil crystallises more readily than that obtained in the preparation of the a-compound. Filter the solid material at the pump, breaking up any lumps as before, wash thoroughly with water and drain. (Yield of crude product, io o-io 5 g.). Recrystallise from rectified spirit until the pure -pentacetylglucose is obtained as colourless crystals, m.p- 130-131° again two recrystallisations are usually sufficient for this purpose. 

As the reaction beings to subside, run in from the dropping-funnel without delay a mixture of 25 ml. of acetone and 20 ml. of benzene, in order to maintain a brisk and continuous reaction. When the reaction finally subsides, heat the mixture on a boiling water-bath for 45 minutes with occasional shaking. If the shaking does not break up the spongy mass of magnesium pinacolate,... 

Place in the flask 2 g. of benzophenone, 15 ml. of isopropanol and 2 5 g. of aluminium isopropoxide. This mixture has now to be heated gently under reflux so that the temperature registered by the thermometer in the column does not exceed 80°, i.e., so that only acetone distils. For this purpose, the flask should preferably be heated in an oil-bath direct heating, even over an asbestos sheet, may cause local overheating and decomposition the use of a water-bath on the other hand may make the column undesirably damp. 

Now cool the mixture thoroughly in ice-water, and run in over a period of 45 minutes a solution of 6 o g. of dry salicylic acid in 75 ml. of dry ether. When the addition of the acid to the stirred solution is complete, heat the mixture under reflux on the water-bath for 15 minutes to ensure completion of the reduction. Then thoroughly chill the mixture in ice-water, and hydrolyse any unused hydride by the slow addition of 50 ml. of ordinary undried ether, followed similarly by 75 ml. of dilute sulphuric acid. 

To purify the crude dinitrobenzene, transfer it to a 200 ml. conical flask fitted with a reflux water-condenser, add about 100 ml. of rectified spirit, and heat on a water-bath until the... 

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