Who invented the mole?

Who invented, or first used, the concept of the mole? I did my own research and the closest I came was Avogadro’s constant, which was made not by Avogadro but rather by Jean Baptiste Perrin. However, I am still not sure of who invented it. I cannot find any information about this, so who, if anyone, invented the mole?

1 Answer

August Horstmann first introduced the concept of gram-molecular weight in the sense of today’s mole concept in 1881. In 1865 Loschmidt first estimated the number of molecules in a cubic centimetre of a gas under normal conditions as 1.83 × 10$^{18}$, and in 1889 Than first determined the gram-molecular volume of gases under normal conditions as 22,330 cm$^3$. This leads to the first estimate for the Avogadro number, see Sarikaya's paper.

However, the conventional story focuses on names rather than concepts, see here for example. The term "mole" was only introduced in 1900 by Ostwald in his chemistry text. He originally defined it as "the molecular weight of a substance in mass grams", but later clarified "that amount of any gas that occupies a volume of 22414 mL in normal conditions is called one mole". Avogadro realized back in 1811 that there is proportionality between the amount of gas and the volume it occupies. Perrin, using moles explicitly, estimated the proportionality constant in 1908 and named it after Avogadro in 1909.