Flask

The oil density at surface is readily measured by placing a sample in a cylindrical flask and using a graduated hydrometer. The API gravity of a crude sample will be affected by temperature because the thermal expansion of hydrocarbon liquids is significant, especially for more volatile oils. It is therefore important to record the temperature at... 

Cryogenics We use several types of evacuated stainless steel cryostats of about 1 htre capacity to provide the 77 K cooling with hquid nitrogen. The simplest, best valued and easiest to handle one is a ordinary thermos flask available from the supermarket (see fig.3). It is sufficient for a measurement period of more than 12 hours. A specially designed stainless steel vessel gains cooling periods of 30 hours. 

This example of high and low pressure also shows the ambiguities of these tenns in science. All these pressures are essentially constant in tenns of tire range of pressures encountered in nature. From negative pressures in solids under tension (e.g., on the wall of flask confining a fluid), pressure in nature increases... 

Nitric acid is prepared in the laboratory by distilling equal weights of potassium nitrate and concentrated sulphuric acid using an air condenser, the stem of which dips into a flask cooled by tap water. The reaction is ... 

Phosphorus pentachloride is prepared by the action of chlorine on phosphorus trichloride. To push the equilibrium over to the right, the temperature must be kept low and excess chlorine must be present. Hence the liquid phosphorus trichloride is run dropwise into a flask cooled in ice through which a steady stream of dry chlorine is passed the solid pentachloride deposits at the bottom of the flask. 

Arsenic present only in traces (in any form) can be detected by reducing it to arsine and then applying tests for the latter. In Marsh s test, dilute sulphuric acid is added dropwise through a thistle funnel to some arsenic-free zinc in a flask hydrogen is evolved and led out of the flask by a horizontal delivery tube. The arsenic-containing compound is then added to the zinc-acid solution, and the delivery tube heated in the middle. If arsenic is present, it is reduced to arsine by the zinc-acid reaction, for example ... 

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... 

Experimental Determination of Boiling-point. Unless only minute quantities of the liquid are available cj. p. 60), the boiling-point is usually determined by simple distillation. For this purpose, the apparatus shown in Fig. 2 is assembled. A distillation flask A of suitable size is fitted to a water-condenser B, the water supply of which is arranged as show-n. An adaptor C is sometimes fitted in turn to the condenser, so that the distillate... 

The thermometer should be so arranged that the top of the bulb is just level with the centre of the side-arm of the distilling-flask. 

This type of filtration is almost invariably performed with the aid of a Buchner flask and funnel, by means of which a rapid and almost complete separation can be obtained. The Buchner flask A (Fig. 4) consists of a simple thick-walled conical flask with a short side-arm for connection to a water-pump. Into the neck of the flask is fitted the Buchner funnel B which consists usually of a cylindrical porcelain funnel, the bed of which is pierced by a... 

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. 

The hot filtered solution is then without delay poured into a lipped beaker or a conical flask not into an evaporating-basin, since it is crystallisation and not evaporation which is now required), the beaker covered with a watch-glass, and then cooled in ice-water. As cooling proceeds, the solution should be stirred from time to time to facilitate crystallisation, and when crystallisation appears complete, the cooling should be continued for at least another 15 minutes. 

When crystallisation is complete, the mixture of crystals and crude mother-liquor is filtered at the pump, again using a Buchner funnel and flask as described on p. 10, and the crystals remaining in the funnel are then pressed well down with a spatula whilst continual suction of the pump is applied, in order to drain the mother-liquor from the crystals as effectively as possible. If it has been found in the preliminary tests that the crystalline material is almost insoluble in the cold solvent, the crystals in the... 

Distillation. If the impurities in a liquid are non-volatile, the liquid may be purified by direct distillation, the impurities remaining in the distilling-flask. This process is therefore essentially the same as a simple distillation for boiling-point determination, and has been already described on pp. 7-9. 

If, however, the impurities are themselves volatile liquids, then the separation of these impurities from the main bulk of the required substance is achieved by fractional distillation. If an ordinary distilling-flask, such as that shown in Fig. 2, p. 8, is used for this purpose, however, only a very partial separation of the liquid components of the crude mixture is usually obtained, unless there is a considerable difference in boiling-point between the impurities and the main component. T0 obtain a much sharper and more complete separation, a fractionating column is employed. 

It has already been pointed out that a liquid even when subjected to simple atmospheric distillation may become superheated and then bump violently in consequence this danger is greatly increased during distillation under reduced pressure and therefore a specially designed flask, known as a Claisen flask, is used to decrease the risk of superheating. In Fig. i2(a) a Claisen flask D is shown, fitted up as part of one of the simplest types of vacuum-distillation apparatus. ... 

Fractional Distillation under Reduced Pressure. One great disadvantage of the simple vacuum-distillation apparatus shown in Fig. 12(a) is that, if more than one fraction distils, the whole process has to be stopped after collecting each consecutive fraction, in order to change the receiver F. This may be overcome by replacing the simple receiving flask F by a pig (Fig. 13) which collects consecutive... 

When a more delicate fractional vacuum-distillation is required, the flask and column shown in Fig. ii(b), p. 26, may be used, the side-arm of the column being fitted directly into receiver C (Fig. 14). A rubber stopper must then be used to fit the flask on to the fractionating column, and it should also carry a capillary tube leading to the bottom of the flask, to provide the usual fine stream of bubbles to prevent bumping. 

The material to be steam-distilled (mixed with some water if a solid compound, but not otherwise) is placed in C, and a vigorous current of steam blown in from D. The mixture in C is thus rapidly heated, and the vapour of the organic compound mixed with steam passes over and is condensed in E. For distillations on a small scale it is not necessary to heat C if, however, the flask C contains a large volume of material or material which requires prolonged distillation, it should be heated by a Bunsen burner, otherwise the steady condensation of steam in C will produce too great a volume of liquid. 

The crude organic material is placed in a porous thimble G (made of tough filter-paper), and the latter placed as shown within the inner tube C. The apparatus is then fitted below to a bolt-head flask H containing the requisite solvent, and above to a reflux water-condenser J. 

Alternatively a mercury-sealed stirrer may be employed. Here again a short glass tube C is inserted through the cork of the flask to act as a collar for the stirrer. The tube C carries a short wide tube B which is either fused at its lower end to C, or is fixed to it by means of a cork as shown. The stirrer D carries a precisely similar tube E, the top of which however is now fixed to D the bore of the tube E allows it to fit easily within the annular space between the collar C and the tube B. Mercury... 

---