Nordic countries that questioned the theory of phlogiston and discussed the role of oxygen in combustion in a modern way. Studies of heat Gadolin studied the relationship of heat to chemical changes, in particular, the ability of different substances to absorb heat (specific heat) and the absorption of heat during state changes (latent heat). This thermochemical work required extremely precise measurements. Gadolin published important papers on specific heat by 1784, and on the latent heat of steam in 1791. He demonstrated that the heat of ice was equal to the heat of snow, and published a standard set of heat tables. Yttrium, the first rare-earth element Gadolin became famous for his description of the first rare-earth element, yttrium. In 1792 Gadolin received a sample of black, heavy mineral found in a quarry in a Swedish village Ytterby near Stockholm by Carl Axel Arrhenius. By careful experiments, Gadolin determined that approximately 38% of the sample was a previously unknown "earth", an oxide which was later named yttria. Yttria, or yttrium oxide, was the first known rare-earth metal compound—at that time, it was not yet regarded as an element in the modern sense. His work was published in 1794. The mineral that Gadolin examined was named gadolinite in 1800. The element gadolinium and its oxide gadolinia were named after Gadolin by its discoverers. In an earlier paper in 1788 Gadolin showed that the same element can show several oxidation states, in his case Sn(II) and Sn(IV) 'by combining itself with larger or smaller amounts of the calcinating substance'. He described the disproportionation reaction: 2 Sn(II) Sn(0) + Sn(IV). Analytical chemistry Having established the composition of Prussian blue, Gadolin suggested a method for precipitating ferrous iron as ferro ferricyanide, preceding the work of Gay-Lussac by forty years. Reports of many of Gadolin's chemical investigations appeared in German in Crell's Chemische Annalen für die Freunde der Naturlehre, Arzneygelahrheit, Haushaltungskeit und Manufacturen. In 1825 he published Systema fossilium analysibus chemicis examinatorum secundum partium constitutivarum rationes ordinatorium, a system of mineral classification based upon chemical principles. The introduction outlines Gadolin's theories, and the text presents mineral species in a systematic ordering. One of Gadolin's latest studies was the chemical analysis of the Chinese alloy pak tong in 1810 and 1827. Also known as alpacca or German silver, it was a less expensive silver substitute often containing copper, zinc, nickel, and tin. Gadolin is also famous for