In 1825 J.F. Engelhard[8] discovere

In 1825 J.F. Engelhard[8] discovered that the ratio of iron to protein is identical in the hemoglobins of several species. From the known atomic mass of iron he calculated the molecular mass of hemoglobin to n × 16000 (n = number of irons per hemoglobin, now known to be 4), the first determination of a protein's molecular mass. This "hasty conclusion" drew a lot of ridicule at the time from scientists who could not believe that any molecule could be that big. Adair confirmed Engelhard's results in 1925 by measuring the osmotic pressure of hemoglobin solutions.[9]
The oxygen-carrying protein hemoglobin was discovered by Hünefeld in 1840.[10] In 1851,[11] Otto Funke published a series of articles in which he described growing hemoglobin crystals by successively diluting red blood cells with a solvent such as pure water, alcohol or ether, followed by slow evaporation of the solvent from the resulting protein solution.[12] Hemoglobin's reversible oxygenation was described a few years later by Felix Hoppe-Seyler.[13]
In 1959 Max Perutz determined the molecular structure of myoglobin(similar to hemoglobin) by X-ray crystallography.[14][15] This work resulted in his sharing with John Kendrew the 1962 Nobel Prize in Chemistry.
The role of hemoglobin in the blood was elucidated by physiologist Claude Bernard. The name hemoglobin is derived from the words heme and globin, reflecting the fact that each subunit of hemoglobin is a globular protein with an embedded heme group. Each heme group contains one iron atom, that can bind one oxygen molecule through ion-induced dipole forces. The most common type of hemoglobin in mammals contains four such subunits.