The Mitscherlich polarimeter with a gas lamp is a classic scientific instrument used to measure the angle of rotation of polarized light as it passes through certain substances. This technique, known as polarimetry, is particularly useful in chemistry for identifying the concentration of chemical substances in solution and determining the purity and concentration of optically active mixtures, such as sugars, amino acids, and various organic compounds.

The device is named after German scientist Eilhard Mitscherlich, who made significant contributions to crystallography and chemistry in the 19th century. The Mitscherlich polarimeter is characterized by its use of polarized light, where the light waves vibrate in only one direction. When this polarized light passes through an optically active substance, its vibration direction is rotated by an angle that can be measured by the instrument.

The inclusion of a gas lamp in the Mitscherlich polarimeter design was common before electricity became a standard light source. The gas lamp provided the light necessary for the measurements, and the use of specific filters or solutions allowed the production of polarized light. This setup was essential to ensure that the light used in the experiments was consistent and suitable for accurate analysis.

Modern polarimeters have replaced gas lamps with more stable and controllable electric light sources, such as sodium lamps or LEDs, offering advantages in safety, convenience, and precision. However, the basic principle of polarimetry, along with the importance of Mitscherlich’s studies in the development of these instruments, remains fundamental to analytical chemistry and other applied sciences.

Ewa Wyka, PhD (Museu da Universidade Jaguelônica, Collegium Maius)