It is quite useful for an apparatus to rest on a platform that can be adjusted up or down. For example, when heating a round bottomed flask in a distillation or reflux, the heat source should be held in such a way that it can be easily lowered and removed from the flask. This is an important safety measure, as it allows for adjustment if the system heats too rapidly (as is evidenced by bumping and foaming), or if anything unexpected occurs (smoking or charring). Removal of the heat source is also of course necessary at the end of a process, and it is best if the heat can be removed while leaving the apparatus intact to cool.
Adjustable platforms come in many forms. A lab jack (Figure 1.43a) is the easiest to manipulate, and can be adjusted up or down by turning the knob. Unfortunately, lab jacks are expensive so are likely to be used in research settings but not in teaching labs. A simple platform can be made from anything stackable, such as wood blocks or KimWipe boxes (Figure 1.43b), although at some height they can be easily tipped. A more secure platform can be created by placing a wire mesh atop a ring clamp (Figure 1.43c).
Adjustable platforms should be used underneath any flask that is clamped in an apparatus well above the benchtop and contains chemicals, especially if they are to be heated or are extremely reactive. If a clamp were to fail for some reason, a platform is a fail-safe and prevents hot or reactive chemicals from falling onto a heat source or splashing on the benchtop where they may become a hazard. Figure 1.43d shows withdrawal of an air-sensitive reagent by syringe, and the reagent bottle is secured by a clamp and supported with a ring clamp/wire mesh platform. If the reagent were to slip from the grip of the clamp, the platform ensures that the hazardous material will not fall.