The first potassium nitrate was transported on 8 December 1911, and two years later the plants were making a profit. Transported cargo increased from 110,000 tonnes per year to 250,000 tonnes in 1915, after the plant had been expanded, and up to 345,000 tonnes in 1917. The small hamlet of Rjukan had turned into a town, and in 1920 there were 11,651 people in Tinn. The 1920 were a tough time, and cargo decreased, but in 1929 the electric arc technology was replaced by the ammonia method, with the main product being potassium nitrate. During the 1930s other products came into production, including hydrogen and other gases, and from 1934 as the first plant in the world mass-produced heavy water.