Prevention of bumping

Prevention of Bumping.—When a substance boils irregularly and "bumps," even boiling can often be obtained by placing... 

Prevention of Bumping. —It frequently happens, especially when the distillation has to be carried out under greatly reduced pressure, that the liquid is liable to boil vith bumping (p. 24) and two methods have been proposed to prevent this. 

For the distillation, the still head consisted of a Claisen-type adapter with a parallel side arm (24/40 standard taper joints), 21 cm. high and 10.5 cm. wide. An ordinary straight still head is attached to the parallel side arm. This large still head prevents any bumping solid from entering the condenser. 

The ammonia can be prevented from bumping by means of a magnetic stirrer in the trap. Heat for the distillation can be obtained from the air of the laboratory and by occasionally flushing the outside wall of the trap with room-temperature acetone. 

The flask to contain the substance to be distilled is fitted with a thermometer and a tube (a) which is drawn out to a fine opening at one end to the other end of the tube is attached a piece of rubber tubing carrying a screw-clamp (b). This tube is provided to prevent violent bumping during the distillation. By... 

If this view of bumping is correct, agitation can decrease or prevent bumping. Sources of inert bubbles could also break the surface and be effective. Inert material such as clean chips of insoluble solids should have no effect. 

There are liquids which cannot be prevented from bumping in this way, and the best plan is then to add a few small fragments of porous porcelain [a clay pipe broken in small pieces answers the purpose very well] or pumice-stone, or both, or a number of small tetrahedra of silver or platinum. A water or oil bath need only be used when a solid substance is present in the flask as, for instance, when a liquid is distilled over lime or phosphorus pentoxide, or when the liquid is liable to decompose when heated with the naked flame. 

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. 

Place about o-i g. of the following substances in a boiling tube and add about 5 ml. of 10% aqueous NaOH solution. Note any reaction in the cold. Then add a small piece of unglazed porcelain (to prevent bumping ), and boil gently for a few minutes. Note any further reaction. 

I) When working with larger quantities of material, it is more convenient (and a better yield is obtained) to purify the air-dried product by distillation under diminished pressure. Use the apparatus pictured in Fig. II, 19, 4, and add a few fragments of porous porcelain to the solid. No air inlet can be employed to prevent bumping since this may lead to explosive decomposition. Collect the pure m-nitrophenol at I60-I65°/I2 mm. always allow the flask to cool before admitting air otherwise the residue may decompose with explosive violence. The recovery is over 90 per cent, of the pure m-nitroplienol. 

The distilling flask. To minimise superheating of the liquid (due to the absence of minute air bubbles or other suitable nuclei for forming bubbles of vapour), and to prevent bumping, one or more of the following precautions should be taken ... 

---