As many readers know, effective September 1, Dow Chemical (DOW) and DuPont (DD) will merge into one company, DowDupont (DWDP). Effective that same day, S&P Dow Jones Indices will replace DuPont, a component of the Dow Jones Industrial Average Index, with DowDuPont. S&P notes,

"Replacing du Pont with the new DowDuPont allows the Dow Jones Industrial Average to maintain its exposure to the Materials sector....The change won’t cause any disruption in the level of the index. The divisor used to calculate the index from the component’s prices on their respective home exchanges will be changed prior to the opening on September 1. This procedure prevents any distortion in the index’s reflection of the portion of the U.S. stock market it is designed to measure."