1.6. Laboratory balances

Digital laboratory balances with of different capacity and accuracy are available for the measurements of the weight of samples and chemicals. Top-loading balances typically work with 0.1 g accuracy in the range from several grams to several hundred grams (Figure 1.11, panel A). For the precise measurement of small weights, analytical balances are used. These devices usually work with 0.01 mg accuracy in the range from 0.1 mg to several grams. A vibration-free, flat and horizontal surface is required for proper operation of such balances—usually a free-standing table with a marble surface plate. Moreover, the convection of the air around the balance should be avoided. (Air currents can exert forces on the pan of the balance comparable to the force exerted by the sample being measured.) For this purpose, analytical balances have a built-in enclosure with doors made of transparent plastic sheets (Figure 1.11, panel B). Measurements can be performed within this protective enclosure. Disposable weighing dishes and laboratory spatulas with spooned ends are important accessories of weight quantification. It is also possible to dispense solids directly into a beaker or a laboratory tube instead of a weighing dish—however, heavy vessels (with a mass above the upper limit of the balance) must not be applied. The mass of the empty dish must be determined first. Then, the display of the scale must be set to show zero by pushing the “tare” button. Next, the substance is added into the weighing dish. The display will thus show the pure mass of the substance.

Laboratory balances

Figure 1.11. A, Top loading balance with disposable weighing dishes, laboratory spatulas and spoons. B, Analytical balance on a vibration-free surface.