For materials that can withstand heat, chemists often use high temperature methods. For example, chemists use tube furnaces to prepare bulk solids. This allows reactions to be conducted up to around . For higher temperatures up to , chemists use special equipment such as ovens made with a tantalum tube through which an electric current is passed. Such high temperatures are at times required to induce diffusion of the reactants. But this depends strongly on the system studied. Some solid state reactions already proceed at temperatures as low as .