Instruments for measuring weights
The balance: a tool that pulls its weight!
One of the characteristics of work in a biology laboratory is that everything must be measured. From powdered products used to prepare various solutions, to the calibration of tubes before centrifugation, even today, the balance remains an indispensable tool.
Miniaturization of the specimens to be analyzed has led to the manufacture of even more precise balances such as the electric balance.
Discover a part of the evolution of balances.
Platform beam balance
This Ohaus brand platform balance is a triple beam poise carriage balance. This type of balance was patented in 1932. To determine the weight of the object placed in the weighing pan, the weights, known as poise, must be moved along the beams for hundreds, tens and units (grams). The beams are horizontal arms to which the pan is fixed. On the opposite side, they are joined together and end in a single arrow. The pan and the arrow oscillate from top to bottom until they stabilize, indicating that the beams are perfectly horizontal. At this moment, the position of the poise indicates the weight of the object placed on the pan. This balance can weigh objects up to 610 grams.
This Toledo balance was manufactured in the USA in 1945. It is based on a system of counterweights: the object to be weighed is deposited on the pan and the counterweight equilibrates the two ends of the weighing arm. A needle indicates the correct reading. This balance can weigh objects up to 2,500 grams.
This balance, used by researchers at the Armand-Frappier Institute, has been used to weigh small animals, among other objects. This model was patented in 1956. The container, equipped with a cover, was used to place the animal safely on the pan. The animal could breathe through the holes around the edge of the container.
Platform dial scale
This Ohaus balance was introduced on the market in 1957. It marked a milestone in the history of this company by introducing a new system of counterweights. Instead of moving the weights along the beam, i.e., the horizontal arm on which the pan is fixed, Ohaus introduced a dial system that was turned to stabilize the beam in a perfectly horizontal position. When the arrow of the beam is stabilized, the position of the dial indicates the weight of the object placed in the pan. This balance, known as a Dial-O-Gram® because of this system, can measure weights up to 310 grams. It was used, for example, to measure small quantities of powder to prepare solutions.
This electric model of a Sartorius analytic or precision balance dates from the 1950s. This unit was acquired and used by researchers at the Institut de Microbiologie et d'Hygiène de l'Université de Montréal in 1964. The analytic balance that can measure precisely very small masses of substances – in the order of the milligram – is essential to laboratory work, especially for chemical analyses. The mechanism is completely hidden in the back and is thus protected from dust and shocks. The glass door on the front opens and closes to allow the user to weigh the samples. Adjustable legs ensure that the instrument is always level.
Electronic analytic balance
This Mettler electronic analytic balance was purchased in 1976 by a research team from the Armand-Frappier Institute. It is an essential laboratory instrument that can measure with great precision very small quantities of solid or liquid material. It is one of the first models of its category to integrate electronics as a basis for functioning. After turning it on, the lateral glass doors are closed and, if necessary, the level is adjusted. The material to be weighed is then deposited in the single pan in a tared cup and the doors are closed, because the smallest draft can affect the measurement. Using the buttons on the front, the weight of the material in the pan can be determined up to four decimals smaller than unity (0.0001 gram).
Balance with cover
This Troemner balance is an example of a precision measuring instrument. The metal case has adjustable feet controlled by a button on the front to correct the level before each new measurement. The glass cover is closed during weighing to ensure that drafts do not modify the weight of the sample placed in the left cup-shaped pan. The counterweight is placed on the right pan. The crank on the right of the case is used for fine adjustments of the measurement by moving a cursor along a ruler graduated to the tenth of a unit (ounce).
Dial torsion balance
This rectangular box is a precision balance known as a “torsion balance” because its functioning is based on the torsion of a metal wire. This type of balance has several uses. In physics, most notably, it is used to measure weak forces (electric, magnetic, and gravitational). This model can be used to determine the weight of small objects. The pans containing the objects to be weighed are hidden under the cover, which contains a window. The cover is closed during weighing to ensure that a draft does not falsify the measurement. The measurement is carried out by stabilizing the balance using the white buttons on the front of the device. One of the buttons is used to fix the grams (up to 10) and the other the tenths and hundredths of grams (0.01g). The balance is equipped with a level that uses adjustable feet. This instrument was used at the Institut de Microbiologie et d’Hygiène in 1977.
A two-pan balance is a device for measuring mass. It is often used to equilibrate, two by two, solutions that will undergo centrifugation. By proceeding in this manner, the volumes may be different, but the weights will be identical. This instrument must be installed on a flat stable surface.
The analytic balance is a precision instrument for measuring mass. It can be used to weigh powder and solutions with remarkable precision down to one ten-thousandth of a gram (0.0001 g). This instrument must be installed on a flat stable surface.