The process differs essentially from the Bessemer process in the refractory lining of the converter. The latter, being made of dolomite ((Ca,Mg)(CO 3) 2) fired with tar, is basic (MgO giving O anions), whereas the Bessemer lining, made of packed sand, is acidic (SiO 2 accepting O anions) according to the Lux-Flood theory of molten oxides. Phosphorus, by migrating from liquid iron to molten slag, allows both the production of a steel of satisfactory quality, and of phosphates sought after as fertilizer, known as "Thomas meal". The disadvantages of the basic process includes larger iron loss and more frequent relining of the converter vessel.