An optical measuring device for measuring the proteins contents of milk comprises a refractometer for meauring the milk refraction value,including a prism,a fixed light source,a lens,a prism supporting element,a photosensitive element for detecting protein contents indicative refraction data,a data display,electric control circuitry and a housing holding the mentioned components a defining a recess for receiving a sample drop to be measured. This device being characterized in that it is based on an electronic read out of the data which are transmitted,in the form of light beams,from the Pulfrick refractometer.
