In the old days, tin ore was smelted in a small furnace approximately three feet high and two feet wide. Strapped with iron, the furnace was being constantly fed with air . Through a bamboo tube , the air was drawn into the furnace. The tin concentrate had to be passed though the furnace five times before the tin was extracted. The tin was then cast into slabs weighing thirty pounds each. The tin production in one season amounted to four thousand Chinese pikuls or 2400,000 kilos. (Sixty kilos equal a pikul.)