Vapour apparatus

Figure 7.2. Schematic diagram of the static mercury vapour apparatus. A Absorption cell B metal support C PTFE tubing D reduction vessel E silicone rubber F magnetic bar G magnetic stirrer H PTFE tubing Iq incident beam intensity I transmitted beam intensity and J exhaust. From [34]...

Clinton, O.E. (1974) Static vapour apparatus for the determination of mercury by flameless atomic absorption. Lab. Pract., 1974, 705-706. 

The trichloride is obtained as a liquid, boiling point 349 K, when a jet of chlorine burns in phosphorus vapour. Care must be taken to exclude both air and moisture from the apparatus since phosphorus trichloride reacts with oxygen and is vigorously hydrolysed by water, fuming strongly in moist air. The hydrolysis reaction is ... 

The basin A is then gently heated by a small Bunsen flame, which should be carefully protected from side draughts by screens, so that the material in A receives a steady uniform supply of heat. The material vaporises, and the vapour passes up through the holes into the cold funnel C. Here it cools and condenses as fine crystals on the upper surface of the paper B and on the walls of C. When almost the whole of the material in A has vaporised, the heating is stopped and the pure sublimed material collected. In using such an apparatus, it is clearly necessary to adjust the supply of heat so that the crude material in A is being steadily vaporised, while the funnel C does not become more than luke warm. 

The hydrolysis of as little as 0 5 ml. of the ester can be carried out in the combined reflux-distillation apparatus shown in Fig. 38 (p, 63). Pass a stream of cold water through the vertical condenser. Place in the 10 ml. pear-shaped flask 0 5 ml. of the ester, 5 ml. of 10% NaOH solution and one or two minute fragments of unglazed porcelain and heat the mixture gently for 15 minutes so that the vapours do not rise more than about half-way up the vertical water ondenser. Now run the water out of the ver ical condenser, insert a thermometer at the top, and pass water through the inclined condenser. Heat the flask sufficiently strongly to collect 1--2 ml. of distillate. This is dilute ethanol. 

Alternatively the semi micro apparatus shown in Fig. 38 (p. 63) may be used. Heat the anilide and sulphuric acid under reflux for 15 minutes in such a manner that the vapour does not rise higher than half-way up the vertical condenser through which water is passed. Then dilute the solution in the flask with 5 ml. of water. Empty the vertical condenser and run cold water through the inclined condenser. Now increase the rate of heating and distil off 1-2 ml. of aqueous acetic acid. 

Nitrobenzene. Usually rather a troublesome solvent, as it is markedly hygroscopic and the freezing-point of the solvent itself tends to fall steadily moreover it is, like benzene, an associating solvent. For a modification of the above freezing-point apparatus, by which the determination may be made in the absence of water-vapour, the student should consult an advanced textbook of practical physical chemistry. 

Carrying out a combustion. The apparatus (Fig. 85, p. 469) will have been left with the bottle W connected to the beak of the combustion tube via the guard tube V and with all the taps shut, the combustion tube, which is dways allowed to cool down while connected to the oxygen source, will therefore be full of oxygen at slightly above atmospheric pressure, thus preventing any leaking in of carbon dioxide or water vapour from the air. 

The high-pressure water supply service is employed for the operation of the ordinary filter pump, which finds so many applications in the laboratory. A typical all metal filter pump is illustrated in Fig. 11, 21, 1. It is an advantage to have a non-return valve fitted in the side arm to prevent sucking back if the water is turned off or if the water pressure is suddenly reduced. Theoretically, an efficient filter pump should reduce the pressure in a system to a value equal to the vapour pressure of the water at the temperature of the water of the supply mains. In practice this pressure is rarely attained (it is usually 4 10 mm. higher) because of the leakage of air into the apparatus and the higher temperature of the laboratory. The vapour pressures of water at 5°, 10°, 15°, 20° and 25° are respectively 6-5, 9-2,12-8, 17 5 and 23 8 mm. respectively. It is evident that the vacuum obtained with a water pump will vary considerably with the temperature of the water and therefore with the season of the year in any case a really good vacuum cannot be produced by a filter pump. 

In order to protect the oil in the oil pump from contamination, some form of trap must be interposed between the distillation apparatus and the pump in order to prevent vapours from the distilling flask, etc. passing... 

A simple form of apparatus is that in which a cooled condensing surface is supported a few cm. above a shallow, heated pool of liquid, and the whole is enclosed in a highly evacuated chamber (compare Fig. II, 26, 1) this offers the least hindrance to the flow of vapour from the evaporating to the condensing surface. The rate of distillation is then determined by the rate at which the liquid surface is able to produce vapour. When the evaporating... 

Some simple apparatus, suitable for high vacuum distillation, are collected in Figs. 11, 26, 1-4. Fig. 11, 26, 1 represents an apparatus, which is particularly well adapted for solids the ground glass joint must be lubricated with a grease of negligible vapour pressure. Hickman s vacuum still is shown in Fig. 11, 26, 2 it is about 60 mm. in diameter. 

A special apparatus (Fig. Ill, 40,1) renders the preparation of iodides from alcohols a very simple operation. The special features of the apparatus are —(i) a wide bored (3-4 mm.) stopcock A which considerably reduces the danger of crystallisation in the bore of the tap of the iodine from the hot alcoholic solution (ii) a reservoir B for the solid iodine and possessing a capacity sufficiently large to hold all the alkyl iodide produced (iii) a wide tube C which permits the alcohol vapour fix)m the flask D to pass rapidly into the reservoir B, thus ensuring that the iodine is dissolved by alcohol which is almost at the boiling point. An improved apparatus is shown in Fig. Ill, 40, 2, a and b here a... 

Excellent results are obtained by passing acetone vapour over an electrically heated nichrome wire spiral an apparatus, incorporating the latter, is described in the experimental section. 

Vinylacetic acid. Place 134 g. (161 ml.) of allyl cyanide (3) and 200 ml. of concentrated hydrochloric acid in a 1-htre round-bottomed flask attached to a reflux condenser. Warm the mixture cautiously with a small flame and shake from time to time. After 7-10 minutes, a vigorous reaction sets in and the mixture refluxes remove the flame and cool the flask, if necessary, in cold water. Ammonium chloride crystallises out. When the reaction subsides, reflux the mixture for 15 minutes. Then add 200 ml. of water, cool and separate the upper layer of acid. Extract the aqueous layer with three 100 ml. portions of ether. Combine the acid and the ether extracts, and remove the ether under atmospheric pressure in a 250 ml. Claisen flask with fractionating side arm (compare Fig. II, 13, 4) continue the heating on a water bath until the temperature of the vapour reaches 70°. Allow the apparatus to cool and distil under diminished pressure (compare Fig. II, 20, 1) , collect the fraction (a) distilling up to 71°/14 mm. and (6) at 72-74°/14 mm. (chiefly at 72 5°/ 14 mm.). A dark residue (about 10 ml.) and some white sohd ( crotonio acid) remains in the flask. Fraction (6) weighs 100 g. and is analytically pure vinylacetic acid. Fraction (a) weighs about 50 g. and separates into two layers remove the water layer, dry with anhydrous sodium sulphate and distil from a 50 ml. Claisen flask with fractionating side arm a further 15 g. of reasonably pure acid, b.p. 69-70°/12 mm., is obtained. 

Method 3. Fit up the apparatus shown in Fig. 7F, 45, 1 using a 250-ml, roimd-bottomed flask. Do not pass water through the glass jacket since the condenser wUl be employed only as an air condenser the empty filter flask is used merely as a trap to prevent the escape of vapours into... 

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