Place the rice in a large bowl and add cold water to cover by 3 inches. Swirl around with your fingers until the water becomes cloudy, then pour through a strainer to drain. Repeat this process until the water remains clear. This will take 4 to 6 rinsings.
Place the rice, salt and the 6 cups water in a deep, nonstick saucepan. Bring to a boil over high heat. Reduce the heat to medium and simmer the rice gently, uncovered, for about 18 minutes. When the rice has absorbed all the water, reduce the heat to the lowest possible setting and sprinkle the butter pieces over the top.
Wrap a clean kitchen towel around the pot lid, piling any excess cloth on top of the lid. (You want to keep the cloth away from the heat) Place the cloth-covered lid over the rice and steam for 20 minutes. Remove the pot from the heat and let stand, covered, 5 minutes.
Gently fluff the rice with a fork and serve immediately.