Laboratory Methods of inorganic chemistry

Аннотация

Large quantities of solutions are concentrated in evaporating dishes, which give a large surface for the escape of vapors from the liquid. They should be heated, unless otherwise directed, with a free flame without wire gauze or asbestos; but the flame should never be allowed to come in contact with the dry upper part of the dish, as in that case superheating would ensue which might result in the breaking of the dish or in the decomposition of the solid material that separates on the sides. Thus as the concentration progresses the flame must be lowered or the evaporation finished on the water bath. Small quantities of liquid can also be boiled down in beakers; but if this is done it is advisable to avoid bumping by stirring or by adding to the liquid such substances as small splinters of wood, bits of unglazed porcelain, or of pumice, or, best of all, some of Siwoloboff's capillaries.