laboratory balances
Introduction
An analytical balance is a type of highly accurate and high-precision laboratory balance, designed to measure small amounts of mass, generally less than a milligram (the most advanced can determine masses with a precision of one hundred thousandths of a gram [0.00001 g or 0.01 mg]). The measuring pans of an analytical balance are inside a transparent box provided with doors to prevent dust from accumulating and to prevent any draft in the room from affecting the operation of the balance. (This enclosure is sometimes called a draft shield.) The use of a safety closure with balanced ventilation, with acrylic aerodynamic profiles designed exclusively for this purpose, allows a continuous air flow inside without turbulence that prevents fluctuations of the scale and allows mass measurements below close to μg to be carried out without fluctuations or product losses. Additionally, the sample must be at room temperature to prevent natural convection from forming air currents inside the box that could cause an error in the reading. Since the analytical balance is extremely sensitive, the weighing can be affected by external vibrations, coming from other laboratory equipment, which is why they are placed on tables or supports with anti-vibration systems.
History and development of the analytical balance
The laboratory balance has its origins in ancient balances with a symmetrical double arm with two plates suspended at their ends (beam balance).[1] The first models were very basic and rudimentary and of poor precision. However, towards the century, more precise and easily replicable models began to be developed. The Scottish chemist Joseph Black is credited with developing, around 1750, a highly precise balance that eventually became an important scientific instrument in most chemistry laboratories.[2][3] Since then, the analytical balance has evolved dramatically over the centuries, although the most significant advances have occurred during the 20th century.
The traditional scale had two pans attached to the end of a bar that pivoted on a blade placed in the center of the bar. The object to be weighed was placed on one of the saucers. Standard weights were placed on the other plate to restore the bar to its original equilibrium position. Weighing with this type of two-arm scales was tedious and time-consuming. In 1946, a single-pan mechanical balance began to be marketed that allowed weighing to be carried out more comfortably and in less time than with traditional two-arm balances.[4]As a result, these balances replaced the previous ones in most laboratories. In these single-pan scales, the pan and a complete set of weights, suspended by hangers, are suspended on the same arm, being counterbalanced by a fixed counterweight on the other arm. These weights can be removed with the help of mechanical systems operated from the outside of the display case. To weigh an object, it is placed on the pan and the scales are rebalanced by removing the necessary weights until the equilibrium position is restored. A mechanical or electrical (optical) scale, depending on the model, indicates the sum of the weights removed, which corresponds to the weight of the object.[5].