What is Refractometry?

Refractometry - a long journey from Plato to Ernst Abbe
It was the philosopher Plato who first described an observation which was important for the subsequent understanding of the refractive index and the associated refraction law. He observed that oars have a normal appearance in the air, while they appear to have a kink under the water.
The first specific representation of the refraction of light was developed by the Persian mathematician and physicist Ibn Sahl in the 10th century. In a treatise on burning mirrors and burning glasses, he investigated the refraction of light and through this work is considered to be the discoverer of the refraction law.
However, his findings fell into oblivion and were not taken up again until six centuries later. Subsequently, the professor Willebrord Snell van Royen formulated a new version of the refraction law in 1621. His findings on the refraction of light at the interface of two transparent media with a different refractive index paved the way for the invention of the refractometer.
It was Ernst Abbe who subsequently presented his refractometer to the scientific community in 1872. It was built at the company Carl Zeiss in Jena. Abbe used refractometers for the examination of balsam and resin as well as for the immersion liquid required in the production of microscopes. His invention is still used today in the fields of education, research, industry and pharmacy.
Digital refractometers are frequently used today. They use LED light sources, prisms and CCD sensors. Digital multi-wavelength refractometers enable measurements at different wavelengths.