Many solids react readily with reactive gases such as chlorine, iodine, oxygen or others. Others solids form adducts with other gases, (for example CO or ethylene). Such reactions are often carried out in a tube with open ended on both sides and through which the gas flows. A variation of this is to let the reaction take place inside a measuring device such as a thermogravimetric analysis (TGA). In that case stoichiometric information can be obtained during the reaction. That information helps identify the products. (By accurately measuring the amount of each reactant, chemists can guess the ratio of the atoms in the final products.)